So does that mean the LBZ pistons arent the weapon of choice?

Admin Edit: I've moved this post along with the rest of the technical discussion about pistons from this thread about the failure of the engine in Nasty Girl to this new thread. It contains some good technical discussion about Duramax pistons and shouldn't be in off topic. -sp33d

I'm starting to hear about more and more cracked LBZ pistons. :(

Would forged pistons work?

i thought forged pistons were standard in diesel:confused:

are the a poor version of them or what????

Didn't they shave the tops a little to get even lower compression? Hmmmm? Or am I wrong about that. Know they use LBZ pistons if I am correct.

Diesel Power has been running LBZ pistons longer than most at high power without issue. He drives it everyday and races/pulls with it on the weekend. If the pistons were at issue here I feel he would have found it long before anyone else. If it's cracked there is an under lieing reason that needs to be found. Most diesel pistons are cast. They have a steel insert in the piston for the rings that needs to be in place for long life so that presents a problem with forged pistons. Pistons just do not crack something has caused it, that is what needs to be found. Who has crack an LBZ piston? If you have did you figure out why?

GM 6.5L Turbo pistons have no steel insert. They are hard anodized on top and in the ring area.

This cracking issue was related to me by the Mahle representative at the AAPEX show.

He indicated the LBZ pistons in racing applications were cracking and that Mahle was getting ready to release a performance line of pistons.

Unfortunately, the Dodge line will be first to be released. :(

Followed by either Ford or Duramax, he was undecided as to which one would be next.

Mahle at the SEMA show had there Duramax piston on display and they have been shipping them already. It is based off there LB7 casting as they were the OEM supplier for those. They are however working on a racing piston as we have been involved with them on it from the start but it's not completed yet. As far as cracked LBZ pistons I haven't heard or seen any but as I stated before there is a reason why it's crack and it needs to be found.

Would the combustion explosion, too early in the upstroke of the piston, after the piston had been heated by an overly long injection duration cycle cause this:confused:

Josh

Would the combustion explosion, too early in the upstroke of the piston, after the piston had been heated by an overly long injection duration cycle cause this:confused:

Josh


ie pre-ignition:rolleyes:

I'm starting to hear about more and more cracked LBZ pistons. :(

This cracking issue was related to me by the Mahle representative at the AAPEX show.

He indicated the LBZ pistons in racing applications were cracking.

Doesn't sound like we have good information here. Kind of sounds like a salesman trying to sell something. I would like to here from those who have cracked a LBZ piston before we say there bad and were hear more and more.....................:( .

Would the combustion explosion, too early in the upstroke of the piston, after the piston had been heated by an overly long injection duration cycle cause this:confused:

Josh


There are lots of possible reasons and that would be one of them. What needs to be found is the one that caused it. Could be tuning, could be bad part, could be something got into the motor or could be improper assemble. Until the cause is found no one will know. Where the crack is in the piston how its shaped and how the metal is around the crack all help in trying to locate the problem.

My "RUDY" went to "Faces of Death "real quick !:(

CSI time ! and TIME will tell !:rolleyes:

holy shart that's bad, I really want to see pics.

This is the second LBZ piston failure I am aware of, first one I have seen first hand. I called the other person that had a failure and we discussed what he seen etc. He was unsure exact cause of failure. It was assembled by himself. He will be sending me pics of the piston so that I may see what, but after describing the failure to me, it happened in the same fashion and in the same place on the piston, directly across the top of the wrist pin.

I have many thoeries to how it could have failed, but first the facts on this one.
Engine ran fine until failure, at which time it devoloped blow by and a miss.
Valve train was 100% intact, nothing bent, out of shape, misaligned and valve adjustment was dead on. Pushrods and valves are in perfect shape, no damage anywhere.

One thing I do find of interest after hearing about other failures and what Mahle themselves have said is the design of the LBZ piston overall. There is indeed more meat in a LBZ piston as compared to a LLY piston, however, its all in the skirt and the bottom of the piston. There is less material in the top of the piston, top being defined as above the pin centerline. The LBZ and LLY pistons both use the same size wrist pin, but the LBZ rides in a bronze bushing with approx measurement of .085" thickness. That removes alot of material from the piston in a critical area. The bushing does nothing to incresase strenght. I compared closely again the pistons tonite and found that while the compression height of the two are identical, the ring pack has been moved to compensate for the larger hole in the piston. The compression ring falls in exactly the same place, but the second ring and the oil ring is just about exactly one ring groove higher to the top in the LBZ piston, thus allowing room for the pin without getting into the ring lands.

I did some rough measureing and found that the hole in the LBZ piston to the outside of the bushing is about 1.580" and the LLY is about 1.355. These are just rough measurements and are not said to be exact, but the results are what I was after. There is nearly .160" larger hole in a LBZ piston, over an 1/8" larger. thats alot of meat to take out of a stressfull area. Is it the problem? Dunno.

I also theorize that we are seeing failures of the pistons based on the fact we improved the rods. Assuming cylinder pressure could be a culprit, we took out the previous weak link with the stock connecting rods with the billet rods. That moves the weak spot to either the crank, bearings, block or pistons. I dont see the crank breaking before a piston and I dont have the bottem end apart to check bearing wear yet. That leaves the piston as the "cusion" for any excesses. I am not a tuner, dont claim to be, dont want to be. There for I am not one to know how/why/when cylinder pressure is excessive.

DieselPro, I do not have the pistons flycut other then to match protrusion heights. Valve clearance is set using a spot cutter in the top of the piston that is large enough to fit a valve.

As for the Mahle aftermarket castings, I've used a couple sets of them now, have another motor at the machine shop getting them as we speak. I am very pleased with them for stock applications. Quality is as good as OEM and they work well. Reason for there use is in situations that require overbore.

Still not convinced myself that the forged pistons will be the best option for the normal use. I am worried about them in a long pull up a grade with a trailer type situation. Racer guys with occasional street use? No problems I would bet. If time permitted, I'd put them in my truck and run it for a year and tear it down and see how they work. I am just a three person shop and I can barely get my own oil changed on time.

Lots more stuff to check tomarrow, as well as tearing down the rest of the engine. I have my build sheet with all the specs from assembly so I will be able to take measurements and see exactly what has changed if anything.

i would like to know what the injection timing was.i too believe too much timing bad!

i would like to know what the injection timing was.i too believe too much timing bad!
I have no idea on that.

Doesn't sound like we have good information here. Kind of sounds like a salesman trying to sell something. I would like to here from those who have cracked a LBZ piston before we say there bad and were hear more and more.....................:( .




There are lots of possible reasons and that would be one of them. What needs to be found is the one that caused it. Could be tuning, could be bad part, could be something got into the motor or could be improper assemble. Until the cause is found no one will know. Where the crack is in the piston how its shaped and how the metal is around the crack all help in trying to locate the problem.

Nasty girl is the second one I have heard about directly from the customer and the Mahle Aftermarket Division is telling me they are developing a stronger piston for racing applications.
Sounds like good information to me. :D

On Edit:
Just saw Eric's post so that makes 3 now that I have heard about. Pretty obvious we are exceeding the piston's ability to handle this much cylinder pressure. Whether or not the cylinder pressure is happening at the right time or not is certainly in question. ie too much timing?

The whole reason behind designing a racing part is so it can handle more stress than a stocker.

Looking at the tune might be a good place to start.

Whos tuning was nasty girl running?

Bobo's

I wonder whos tuning was in Roger's truck....

Nobody here is pointing fingers. Facts will tell the tale not assumptions!:)

Nobody here is pointing fingers. Facts will tell the tale not assumptions!:)

Keith,

IMHO your runnning more cylinder pressure than most anyone else. Your failure could have been caused by simply making more power than the piston could withstand.

I agree, at this point I feel it will be hard to determine the exact cause, so no use making assumptions that can't be proven.

Keith,

IMHO your runnning more cylinder pressure than most anyone else. Your failure could have been caused by simply making more power than the piston could withstand.

I agree, at this point I feel it will be hard to determine the exact cause, so no use making assumptions that can't be proven.

This is why I love "The Place", honest unbiased help and opinions!

Thanks Guy!

If this is the case and the only failure found internally, what are my options if any for pistons? As most of you know I built this truck not to be a trailer queen but to withstand the abuse of a day at the track and still take my son too school everyday. :)

As of right now there is not many choices for pistons and for a daily driver and weekend racer I still feel the LBZ is the best one out there. As for a trailer queen that will see few miles of use, a forged piston may work just fine. The new piston we have worked with Mahle on should be a good part but until the first articles are made then testing done i cannot say one way or the other about it.

Diesel Power and Nasty Girl both have motors that are very close to being the same thing. Diesel Power started with an LB7 assemble and Nasty Girl started with an LLY assemble. Both used the same rods, camshaft and pistons, both have made near the same power output on the dyno. Diesel Power's engine is running fine with over 5000 miles of use and lots of those miles are hard racing miles. I do not believe Nasty Girl made it that long or made any races. Diesel Power runs a big single turbo @ 65 psi, Nasty girl runs twins at ? psi. So why would one fail and not the other?

Until the problem is found no one will know, right now all we know is Eric found a crack in a piston and if Rogers motor cracked a piston they need to be compaired and find whats common between the two. This will give a direction to help try and locate the problem.

As of right now there is not many choices for pistons and for a daily driver and weekend racer I still feel the LBZ is the best one out there. As for a trailer queen that will see few miles of use, a forged piston may work just fine. The new piston we have worked with Mahle on should be a good part but until the first articles are made then testing done i cannot say one way or the other about it.

Diesel Power and Nasty Girl both have motors that are very close to being the same thing. Diesel Power started with an LB7 assemble and Nasty Girl started with an LLY assemble. Both used the same rods, camshaft and pistons, both have made near the same power output on the dyno. Diesel Power's engine is running fine with over 5000 miles of use and lots of those miles are hard racing miles. I do not believe Nasty Girl made it that long or made any races. Diesel Power runs a big single turbo @ 65 psi, Nasty girl runs twins at ? psi. So why would one fail and not the other?

Until the problem is found no one will know, right now all we know is Eric found a crack in a piston and if Rogers motor cracked a piston they need to be compaired and find whats common between the two. This will give a direction to help try and locate the problem.

Just to clarify I have allways had an LB7 NOT LLY. And also at the time of failure the twins were running at 70-75 psi boost.
Diesel Powers with the exception of the twins is the same as mine. Only other difference to the longblock that I am aware of is my heads from Redline Diesel Performance. I can also assure you that Rogers failure is completely unrelated to mine.

Rogers failure and Keiths failure are completely different. Rogers failure has been identified and as soon as the currently being developed parts are done, it will be reassembled. It will still be a test as the new components going into it have not been used yet.

I still dont see how the LBZ piston is so superior, Sure, its got coated skirts and lower comp, but I see no advantage to the bushed wrist pin. For that matter, I see no advantage to the coated skirts. Lower drag on the cylinder walls, sure. Could one show me how it makes any gains? I've never seen a LB7piston with skirt wear.

After seeing/hearing of other LBZ piston failures not related to me and Mahle themselves acknoledging piston failures, I'm starting to wonder if they are so great for high hp applications.

More diagnosis/inspection is underway over the next couple of days to see if we can learn more on Keiths motor.

Sorry Kieth I thought I was told you were LLY based. The heads should have little to no affect to a cracking piston unless there was valve contact and I'm sure if that happended Eric would have siad so.. So in trying to find things that were different were down to your boost was about 10 psi more than Diesel Powers boost. Was this boost there most of the time or just happened to be that high when the failure occured?

Sorry Kieth I thought I was told you were LLY based. The heads should have little to no affect to a cracking piston unless there was valve contact and I'm sure if that happended Eric would have siad so.. So in trying to find things that were different were down to your boost was about 10 psi more than Diesel Powers boost. Was this boost there most of the time or just happened to be that high when the failure occured?

The pistons were inspected and no valve contact was found. After furthur inspection of the heads Eric found them to be in perfect shape.

The boost pressure we were seeing with the single CP3 was between 65-70 psi. On the day of failure the dual CP3's were running for the first time and the boost pressure we seen that day was around 70-75 psi . I spoke to Nathan and adjusted the wastegates on the twins to run lower PSI prior to running the dual fuelers.

IIRC Crank It Up is running boost levels in that range or higher and has had no failures. Also Clint from ATS is running compounding turbos at much higher boost levels than I at this point with stock gaskets, lbz pistons and studs , same as me.

I still dont see how the LBZ piston is so superior, Sure, its got coated skirts and lower comp, but I see no advantage to the bushed wrist pin. For that matter, I see no advantage to the coated skirts. Lower drag on the cylinder walls, sure. Could one show me how it makes any gains? I've never seen a LB7piston with skirt wear.


Take a look at the piston a little closer and you will find there are quit a few differences, some you can see and some you cannot. The LBZ piston has lower compression by moving the bowl and volume of the bowl in the piston. To do this things had to be moved to keep material thickness the same or greater in some area for greater strength. Weigh an LB7 Vs LBZ piston and you will see material has been added as the LBZ has a larger bowl volume which removes material but yet weights 70 grams more. The LB7 piston has a longer skirt than the LBZ so its not there. The LBZ uses a longer wrist pin to spread the load out over more area of the piston and a bronze bushing to reduce the friction. The LBZ is a stronger better part than the LB7 units in many ways. This is also why Mahle is taking there time to get a unit that is better than the LBZ unit. When we started with them everything was going along find until the LBZ piston got back to them. The engineer I work with said we need to stop as the LBZ was much stronger and we need to be better than that.

Unless there was just a bad part (which happens) there is another cause that cracked the piston it just needs to be found so it doesn't happen again.

Whats the criteria for quality control with the pistons?

What is the difference in rods between the LB7 and LBZ? I have heard the LBZ rods are stronger. Any truth behind this.

What is the difference in rods between the LB7 and LBZ? I have heard the LBZ rods are stronger. Any truth behind this.

Yes, GM improved the rods in the LBZ

The LBZ piston failure reminds me of what would happen to a KB Hyperutectic piston in a gas motor when subjected to detonation. It basically cracked or exploded.

Mahle is the OEM supplier of pistons for the GM LS-1 program, and these cast pistons tend to come apart at high power levels as well. They are being pushed well beyond their design criteria. :eek:


All of these pistons LBZ, LLY and LB7 are still "cast" pistons and now that we have fixed the rod bending problem, the piston seems to be the next weakest part to fail.

I'm sure Mahle will address this with different alloys in their racing program, but there is only so much that can be done with a cast part. Now that I have a contact at Mahle I will actively participate with input in this program.

In an ideal situation Mahle could make a forged piston with the cast iron insert for the top ring.

Until then we may be stuck with making a choice between exploding "cast" pistons at extremely high cylinder pressures or the perceived accelerated top ring land wear of a forged piston over time.

No right answer here, we are all on a journey of discovery. :D

Thanks to all of those who are willing to invest the time and money in pushing the limits. :ro)

Its fun to be part of development like this, but very frustrating with things like this.

Steve, I was aware of the differences in the two pistons you mentioned, but I guess my concern is if its enough. Yes, its better then the LLY/LB7 units, but its better at what? More meat, yup, more pin contact, yup. Heavier? Sure, but non of that make it stronger. I have LB7 and LBZ pistons here that are cut up and nothing shocks me. I'll work on getting some pics of them side by side and post.

eric,

what were the failures on the lly and lb7 pistons?

Steve, I was aware of the differences in the two pistons you mentioned, but I guess my concern is if its enough. Yes, its better then the LLY/LB7 units.

I would love to see the finish part from Mahle as I'm sure it will surpass the LBZ but we cannot get any yet. How long or how good they will be is still up in the air. Once it is done then it still needs to be tested to make sure it does what it's suppose to and that means assemble another motor and beat them up and see what we see. For now the LBZ is the best we've got to work with so what do you do other than live with it.
My hope is you can trace down the real problem so it can be prevented in the future whatever it turns out to be. They do not call it being on the bleeding edge just for the fun of it, cause you do get bloody every now and again.
How do the bearings look from the affected cylinder?

I think the highest timing we ran was in the neighborhood of 23* so I doubt that was the cause.

There is a very good reason you will not see many cast aluminum parts in a production aircraft that are in high stress areas. They are nearly always forged. While a casting might have similiar initial yield strength, time works against castings. Much harder to get a forging to crack. They tend to bend.

Wonder when Mahle is gonna make a coated, low compression, bronze bushing, deep skirted 800+HP piston for my 6.5? :D

DieselPro, I do not have the pistons flycut other then to match protrusion heights. Valve clearance is set using a spot cutter in the top of the piston that is large enough to fit a valve..

I didn't think y'all cut the piston tops and I thought somebody had mentioned it and I was wondering about that.

Are the pistons hard anodized? Anodizing the tops after any machine work might improve the strength somewhat. Not a fan of ceramic coating pistons.

Cylinder pressure spikes would do a number on the piston. Granted you do have to make pressure to make power. The more efficient the engine becomes the less timing that is necessary. In your case I am sure the timing could be backed way up under max boost. Only one problem there is you only have a few milliseconds to get all the fuel in there. Retarding the timing cuts back on getting all the fuel in at the optimum time.

Looking forward to seeing some pics. Thanks for spending the time with us.

How come diesel power makes so much boost with an aurora, doesn' t he have ported heads? shouldn't that cause a boost drop?If his numbers are that high which I believe they are, they are higher then all other aurora trucks (with stock heads even) that i have heard of.
MY aurora leveled off around 42psi spiked to 46ish, good enough for 11's on #2, and attleast a 6psi drop from stock heads. I assume nasty girl has had a similiar boost drop which would construe results between the 2 motors as far as boost/cylinder pressure comparisons go.

:exactly: :confused: How come diesel power makes so much boost with an aurora, doesn' t he have ported heads? shouldn't that cause a boost drop?.

I thought Nicks boost number was a little high as compared to other A5 trucks I know off, but not being in the drivers seat of one everday, I was unsure exactly.

As for coatings go, I have talked to guys in the Dodge world ( Garmons ) and they are coating the tops of the pistons with something, dont recall what though. Basically trying to combat heat.

I am very interested in seeing what develops in the future in the piston area. The ultimate piston would be a forged unit that was able to utilize some type of cooling channel behind the rings and have a steel insert in the compression ring for the keystone rings. I dont see that happening anytime soon though.The Dodge guys do not have a cooling nozzle, yet they seem to hold togather well?

eric,

what were the failures on the lly and lb7 pistons?


I have yet to see any failures as a result of piston problem.

lbz are not the only one cracking pistons.I have an lly thatcouldnt have cracked any straighter if i had used a saw.i would like to see what everyone is runnining for timing and maybe pulse width at say 3100rpm.

Nick's heads are from the same machine shop as Nasty Girls and Dale's heads. Nasty Girls heads had bigger exhaust valves install and Nick used the stock size valves. His A5 for whatever reason has always made more boost than most others but if we look at the dyno results Nick @ 675 and Nasty Girl was @650 as I recall. When Nasty added the dual CP3 his numbers are sure to have gone up but my point is both motors are the close to the same and both motors make close to the same power output. One failed with few miles on it and the other with lots of miles and racing and is still running fine. What we need to do is find what caused the one piston to fail so that it does not happen again and I do not believe its because of the parts used for the reasons stated above.

why are the lbz pistons being touted as the choice of pistons, if the lly/lb7 pistons arent having the failures that the lbz is.

How come diesel power makes so much boost with an aurora, doesn' t he have ported heads? shouldn't that cause a boost drop?If his numbers are that high which I believe they are, they are higher then all other aurora trucks (with stock heads even) that i have heard of.
MY aurora leveled off around 42psi spiked to 46ish, good enough for 11's on #2, and attleast a 6psi drop from stock heads. I assume nasty girl has had a similiar boost drop which would construe results between the 2 motors as far as boost/cylinder pressure comparisons go.Just for conversation we have always been in that neighborhood with boost levels similiar to Nick's.Even with single cp3,stock intake,and stock heads.New motor Toman intake,stock heads and dual cp3s.NLDP

why are the lbz pistons being touted as the choice of pistons, if the lly/lb7 pistons arent having the failures that the lbz is.

I've seen many more LB7/LLY pistons fail than I have LBZ. The LBZ is flatout a stronger piston then the earlier unit so that's why we use it. Can it be done without it sure but if your doing a rebuild why not start with the best part you can get to start with. We've got one reported failure and do not know why with a LBZ piston.

Eric

How were the bearings in the affected cylinder? How was the glow plug?

Scott, did it crack across the pin? Was there any wear on the piston anyplace. I have seen other piston failures on engines, but I have just wrote them off as injector failure. Basically the injector is acting like a water jet machine and cutting a hole in the piston, this causing it to crack. However, as I sit here and type this, I am thinking and every single one of them is cracked across the pin and that is where I see the wear also. What happened first?

Dang it, I got to dig up some old parts in the morning. Its very possible I have seen this many times before but just assumed an injector had failed....

Eric

How were the bearings in the affected cylinder? How was the glow plug?
Steve, Glow plug looked perfect, no issue at all. I have not torn down the engine to inspect the bearings yet.

Never fails. The more you know, just shows how much you don't know.

Picture of piston in question? With piston cooler.

http://dieselplace.com/forum/attachment.php?attachmentid=28237&d=1163085227

yup, you can see the oiler in that pic as well

Is the piston pin press fit? or held in with snap ring?

Once the piston starts to crack the cylinder pressure could "open" a hole?

Big hole in pocket book. Crack will just loose all the compression real quick.

I think the highest timing we ran was in the neighborhood of 23* so I doubt that was the cause.The peak timing number may not necessarily be the cause but the timng curve could be. Anyone can make the mistake of kicking the timing in to soon. And one thing that most don't take into account is that boost is essentially timing. These engines in this aspect are similar to gas engines. If you add air you generaly take timing out of it.

This is not meant as a flare. Just an FYI.

I know on the alcohol cars when we would blow a head gasket it would torch a trough as the pressure escaped. Same principle here.

:exactly: I know on the alcohol cars when we would blow a head gasket it would torch a trough as the pressure escaped. Same principle here.

i don't know why it makes the boost it does. the motor pulls so much stronger up high than it did with the old engine maybe the cam has something to do with it? for the record with the single cp3 i would run a sustained max of 55 psi. if it wasn't really loaded down hard then it would run about 50. since adding the dual cp3 i've seen 60+, but the tuning hasn't changed since june. my old engine's boost when down just a titch when we put the new heads on it. maybe the new motor would be a bit higher with stock heads. i would think so but who knows. i've got 10,000 miles on the motor so far with zero engine problems.

How come diesel power makes so much boost with an aurora, doesn' t he have ported heads? shouldn't that cause a boost drop?If his numbers are that high which I believe they are, they are higher then all other aurora trucks (with stock heads even) that i have heard of.
MY aurora leveled off around 42psi spiked to 46ish, good enough for 11's on #2, and attleast a 6psi drop from stock heads. I assume nasty girl has had a similiar boost drop which would construe results between the 2 motors as far as boost/cylinder pressure comparisons go.

Keep In Mind, This Platform Is Designed For 300 Hp, At 2x And Still Running, It Is Only Time Till A Hard Part Fails.

Those Of You Looking At Tuning For A Solution To This Are Kidding Yourself's Or Don't Know Enough About Engine Building.

There Will Always Be Failures When You Over Hp A Hard Part. As With Our Sister Gas Parts, As Hp Went Up So Did The Technology With Better, Stronger, Lighter, Higher Hp Capable Parts.

I dont see it fair to blame tuning on anything. We have no proof of that.

Nick's motor is not a benchmark for building, it runs good and all, but if its the magic bar we are going for.....I've got a dozen other motors out there running fine in closer to stock trim that we have built for "regular" guys and they are working fine. Keiths motor has alot of stuff on it that nobody else has. Rogers motor had a failure that was identified and fixed.

Putting blame in one blace or another with out facts just starts problems we dont need right now. It impedes development and moving forward.

Temper temper temper,you know what and who I am referring to as I had to clean up this thread.
There is no need to make accusations or flame until the evidence of the failure is brought forth.
Letting you know that if it continues there will be repercussions.

This is an extremely interesting thread. Keep'm in check Mackin, I'd hate to see this one die.

Eric, any pics of the broken piston? Have you checked for chrush on the bearings? Is there any chatter marks on the bearings? I know that when I was crewing for a TAH that when we started to get chrush on a rod bearing then we were on the ragged edge. We considered .002-.004 of crush a good tune-up. Granted we changed the bearings every pass if there was evidence of crush. If that motor had good oil pressure then I doubt there is any crush on the bearings.

There have been so many "hidden" engine losses that to actually see a discussion of an engine failure in public like Nasty is somewhat unique.

It is appalling to see blame heaped on the tuning. Many of the folk posting in this thread HAVE seen cracked pistons before, but apparently they choose not to go public with that they've seen, and instead, just discuss failures that they were not personally involved with. While most have been drug related, there have been cracked pistons with even "mild" tuning.

I would suggest the "experts" who have seen cracked pistons before step up to the plate and discuss what they saw with the trucks they have personal knowledge of. And tell the whole story. I'm not at liberty to discuss any of the engines since the information was given to me in private by them.

Readers: Don't believe this case is unique, or even rare in bombed Dmaxes. Neither is true. Just the information is not "public". Perhaps they would be more apt to post about the other losses if we as a community did not jump on them pointing fingers. And yes, I am guilty as well; I suggested awhile back too much timing with nitrous is lethal, which was only a guess. I have since made a rule not to blame tuning without hard proof.

Pat good post. I have no problem with open discussions if its benificial. The flameing will do nothing but shut down public conversation on the matters.

I've got some phone calls to make....

I just finished reading this entire thread and for those of us sitting on the fence getting ready to build a super engine I'm really confussed. It would be great to see some pictures of the failures, it wouldn't mean much to me but maybe help those of you who have experience in engine building. My new truck while it is going to be street legal probably will not be driven to the races, in fact I know it won't. Would like to have the best pistons I can get for the build. Right now the LBZ piston still looks like the one to get. Dumb *** question, when you build an engine like Nasty Girl's or Nick's how do you break them in? I have always broke a new vehicle in hard. Wanted it to break right off the get go if it was going to. Those were stock engines and under warranty. These are different, lots of power and has been stated, looking for the next weakest link. Do these need a longer easier break in or balls to the wall from the get go?:confused:

Boy, guess I missed all the flaming post, as Makin must have clean it up pretty good. Most of the failures I have seen have been from everyday driven trucks and what was or was not run in them is unknowen so to gain any useful knowledge was useless. One motor broke a valve at the weld between the head and the stem of the valve. The Race motor failures we have seen all have been cause by rod failures. The rod failures have been caused by overpowering the motor both with and without drugs being involved. Now that we've fixed the rod issue the next weak link will surely show itself. What we do have here to compare are two motors that are built with the same parts and one has failed. It's rare that you get to have 2 the same to compare and it will help identify what happened. It could be as simple as a part failure or it could be something else, at this point no one knows.

This may sound stupid but what about quality control on the piston?
If I remember from the begining of this post it was only one piston that failed,how about the other 7, they were under the same stress, what signs do they show if any?
I just wonder since they are factory LBZ cast pistons being subjected to 2x or more than the design parameters a piston that was just not quite up to par even though it would last forever in stock configuration could/would it not be a weak link?
These pistons are mass produced without any thoughts of racing type of loads ever occuring.
Just a thought.
Merle

Scott, did it crack across the pin? Was there any wear on the piston anyplace. I have seen other piston failures on engines, but I have just wrote them off as injector failure. Basically the injector is acting like a water jet machine and cutting a hole in the piston, this causing it to crack. However, as I sit here and type this, I am thinking and every single one of them is cracked across the pin and that is where I see the wear also. What happened first?

Dang it, I got to dig up some old parts in the morning. Its very possible I have seen this many times before but just assumed an injector had failed....
straight with the wrist pin and down both sides.cracked right into the wrist pin holes.thats the only thing that kept it from cracking all the way down the skirt.

I'm with 80K10, I work for the OEMs and quality controls are often lax as long as the part will perform as designed. Diesel Tech, is there any kind of inspection, be it visual or more technical done on LBZ pistons before there installed in such applications?

One thing to remember here is that the reason that the LBZ piston is heavier than the LB7/LLY and appears to have less material is because the density and type of the material used is much higher in the LBZ pistons then the LB7. Usually denser material means harder material, harder material usually means it's stronger but also more brittle.

I had heard that there was also a chemical hardening process on the LBZ pistons to make them less prone to cracking, I would imagine that if that's true taking material off the top would then eliminate some of that strength and the pistons would be more prone to cracking under stress.

Just my .02

Cheers,
wade

P.S. Good luck Keith, pushing the limits can be a real pain.........Literally!!

I keep seeing referrences to the engine components are being pushed at twice their intended design. This isnt true guys. A basic rule of engineering thumb is to build a machine or piece of equipment and rate it to operate at 75-80% of its max capability. In building engines, especially diesels, this rating is a bit closer to 60-65%. An LBZ engine is producing 360HP at 650 ft-lbs of torque. This is by no means its max rated capacity or we would see them blowing up left and right with just a 60hp Edge tune thrown to them.

I'm with 80K10, I work for the OEMs and quality controls are often lax as long as the part will perform as designed. Diesel Tech, is there any kind of inspection, be it visual or more technical done on LBZ pistons before there installed in such applications?

As I've said it could have been just a bad part, as far as inspection of the piston before installation that would have been done by the engine builder so you would need to ask Eric. We just supplied the rods and camshaft for Nasty Girl. Nicks motor was built useing the same parts so it gives us something to base some decisions on, but the 2 motors were machined and assembled by different people. If we can figure out what is different then there is a chance of finding the cause of the failure so it does not get repeated.

I had heard that there was also a chemical hardening process on the LBZ pistons to make them less prone to cracking, I would imagine that if that's true taking material off the top would then eliminate some of that strength and the pistons would be more prone to cracking under stress.

Just my .02

Cheers,
wade



So that would make fly cutting valve relief a big no-no.

Were the LBZ pistons machined at all for these 2 engines? Thought I'd heard, that to have the bigger valved heads work, the pistons needed to be cut or indexed. Same heads?, piston clearances for both?

I may be way off though.

So that would make fly cutting valve relief a big no-no.

That's a big "10-4"

It makes sence that they would have them hardened with a denser material, whether or not it's fact is still to be known. But since it would add up to why these failures happened I figured it was good to post the idea so inquiring minds could look into it further.

I know that with Clint's truck we have not cut or modified the pistons in anyway and when we pulled the heads they showed no signs of cracking.

Were the LBZ pistons machined at all for these 2 engines? Thought I'd heard, that to have the bigger valved heads work, the pistons needed to be cut or indexed. Same heads?, piston clearances for both?

I may be way off though.

Yes all the motors that have gone down with cracked pistons have been cut or modified. There was another motor in Cynthiana that went down the same way with the same piston mods.

By "chemical hardening" are you talking about a coating or something? (That may be a dumb question, but its honest :) )

Was it running water/meth when it let go? If so, in what ratio?

At face value, I don't see how Michael asking who made Roger's tune was inflammatory. As everybody has said this needs to be viewed from every angle, and to me it seemed like he was being very reasonable & just speculating. He didn't point a finger & say "it was the tuning!" he just asked who did it, the same as others have asked "whose turbos were on there?" etc.

Maybe more was revealed in posts that were "cleaned up", but it seems everybody was quick to jump on him about finger-pointing, and he wasn't given a fair say in this thread out of fear he may say something unfair. That's no good for anybody either reading this thread or involved w/ the situation directly.

Yes all the motors that have gone down with cracked pistons have been cut or modified. There was another motor in Cynthiana that went down the same way with the same piston mods.

All the motors? I am curious as too how many we are talking here and why are these failures just surfacing now or are they recent? Are these modified or stock motors? More info please Wade!:)

By "chemical hardening" are you talking about a coating or something? (That may be a dumb question, but its honest :) )

Was it running water/meth running when it let go? If so, ratio?
This build was a fuel only application from day one..... and allways will be!

Nasty Girl, sounds like you have the same problem I have. Pissed'n'Broke ):h

Both motors had valve reliefs added to the pistons for piston to valve clearance. This is a common practice so I do not think it a source for the problem. Since it's in both motors one would think they should have both done it and they have not. The only other failure I know of has had the problem located and it had nothing to do with Valve reliefs being added. As for LBZ pistons being coated they are only coated on the skirt nothing on the rest of the piston. As for hardening of the material I think that's more wishful thinking. I have a set here and can scratch the surface with no more pressure than a raw piece 5052-T0. Anyone who knows Aluim. knows 5052-T0 is dead soft material.

I missed all the flames as well. Oh well not really condusive to learning anything any way.

I had a few thoughts I would like to share:

1) The forces from cylinder pressure are transferred through the top of the piston to the wrist pin.

2) From the wrist pin to the rod.

3) From the rod to the crank and so on.

4) Previously at high cylinder pressures we would bend rods.

5) Now we are cracking pistons parallel to the wrist pin.

Picture the piston in a hydraulic press being supported only by the wrist pin and pressure being applied to the top of the piston by the press ram. Where is it going to break?

Correct, it will crack and split apart across the piston parallel to the wrist pin.

Which will split first a cast or a forged part?

IMHO the only reason to stick with a cast piston with a cast iron inserted ring land is for fear of top ring land wear. Realistically we don't really know how long a forged part will last. So to be afraid of a forged piston without the cast iron ring land at this point is a little premature.

High cylinder pressures are going to occur due to any number of factors including boost, fueling, nitrous, too much timing etc. The bottom line is in building a competition engine we use the strongest parts available to allow for the occasional oops in boost, or timing or rpm or whatever. It's all part of the racing game.

Cutting valve reliefs in a piston is a function of cam lift, duration and lobe seperation on a Duramax motor and has nothing to do with the diameter of the valves as we are dealing with a zero degree valve angle engine.

:D

Picture the piston in a hydraulic press being supported only by the wrist pin and pressure being applied to the top of the piston by the press ram. Where is it going to break?

Correct, it will crack and split apart across the piston parallel to the wrist pin.

Which will split first a cast or a forged part?

IMHO the only reason to stick with a cast piston with a cast iron inserted ring land is for fear of top ring land wear. Realistically we don't really know how long a forged part will last. So to be afraid of a forged piston without the cast iron ring land at this point is a little premature.

Several things I see wrong with these statements. First off the piston will fail at it's weakest point which may or may not be parallel to the pin. Second if the machine work done to the piston caused a void or a hairline crack it would break or crack there. As far as sticking with a cast piston the Keystone ring has been proven to tear up pistons without a steel insert, that is years old information and well proven in the diesel world. Now if they come up with a way to make a keystone ring live in a forged piston I would give it a shot but to date several companies have tried with no success. So to use a forged piston today you would need to go to a gasoline type ring package and guess what they do not live in the diesel world well, again well proven many times over.

The biggest issue is no one knows what happened and why, so to try and make general statements about possible part failures is just that, a general statement that may or may not have anything to do with what happened. Let's wait and see what Eric finds then we may have something to go on.

i have seen in some road racing application which not only hardens the imediate surface but the enternal integerty as well. though it is rather expensive.
http://www.onecryo.com/onecryo/motorsport-wcsdec97.htm


food for thought.......

It would be nice if the Crank it up guys put in there 2 cents. I'm sure with the power there running they may have seen some of these problems?

All the motors? I am curious as too how many we are talking here and why are these failures just surfacing now or are they recent? Are these modified or stock motors? More info please Wade!:)

I'm not at liberty to disclose the name of the person, but there is a motor in Cynthiana KY that just cracked 4 LBZ pistons and split one in two peices, there are several here on the board that know who I'm talking about.

Your truck Keith would make the second one that has split an LBZ piston, and it's undisclosed what happened to Rogers truck, whether it be split piston or something else.

Kyle Michael on the other hand has been running more boost, more fuel & more HP then anyone I can think of, with cut LB7 pistons and billet rods and hasn't had not one issue with the bottom end. Just some food for thought.

Have a good weekend.

interesting

Several things I see wrong with these statements. First off the piston will fail at it's weakest point which may or may not be parallel to the pin. Second if the machine work done to the piston caused a void or a hairline crack it would break or crack there. As far as sticking with a cast piston the Keystone ring has been proven to tear up pistons without a steel insert, that is years old information and well proven in the diesel world. Now if they come up with a way to make a keystone ring live in a forged piston I would give it a shot but to date several companies have tried with no success. So to use a forged piston today you would need to go to a gasoline type ring package and guess what they do not live in the diesel world well, again well proven many times over.

The biggest issue is no one knows what happened and why, so to try and make general statements about possible part failures is just that, a general statement that may or may not have anything to do with what happened. Let's wait and see what Eric finds then we may have something to go on.

I'm making general statements to help the discussion along. I'm sorry you don't approve.

Dealing in absolutes doesn't leave room for anybody else's opinions that may differ from your own.

The Keystone ring package/iron inserted piston is great at keeping the ring from sticking in the land from soot build up and/or excessive heat at the piston crown, two things that are very evident in a Diesel engine.

Today's common rail motors have far less soot deposits than the diesels of yesterday, so previous experiences with "gasoline type ring packages" from any 7.3L or 5.9L engines are not necessarily applicable in this case.

Ceramically coat the top of the piston to keep the heat out of the top of a forged piston and I believe we could get a "gasoline type ring package" to work just fine.
In fact there may some that are already doing it that way.........................

Picture the piston in a hydraulic press being supported only by the wrist pin and pressure being applied to the top of the piston by the press ram. Where is it going to break?

Correct, it will crack and split apart across the piston parallel to the wrist pin.

Which will split first a cast or a forged part?



Your statements you made sure read like absolute facts when there not, I just pointed it out so as not to confuse those who do not know better.

There are several companies in the last 2 years that have tried coatings with gas engine type rings in HD diesels. They have failed in all long term type testing. For a race only application they seem to be working but that means tearing the engine down and replacing them every race season and sometimes more often. I would love to see a better solution but, as of right now there is not one I've seen or heard of that is working for long term. Some of the piston suppliers have given up for the time being but as technology changes I'm sure something will come along.

I'm not at liberty to disclose the name of the person, but there is a motor in Cynthiana KY that just cracked 4 LBZ pistons and split one in two peices, there are several here on the board that know who I'm talking about.

Your truck Keith would make the second one that has split an LBZ piston, and it's undisclosed what happened to Rogers truck, whether it be split piston or something else.

Kyle Michael on the other hand has been running more boost, more fuel & more HP then anyone I can think of, with cut LB7 pistons and billet rods and hasn't had not one issue with the bottom end. Just some food for thought.

Have a good weekend.

Ok so from what I understand here we now have 2 motors that have had cracked pistons that are cut (Myself and this motor in KY), and we have 2 motors that have cut pistons that are fine (Nick and Kyle). So what are we saying here?
It seems to me some are saying the pistons fail for various reasons....that I can understand. What I don't understand is how can we point the finger at any one thing going by the 4 trucks above. 2 have failed 2 have not.....if this is true then speculation is all we have and no facts. There is just not enough evidence to prove otherwise. There are very few motors in this "Catagory" to think otherwise. Am I wrong? :confused:

And I will say it again Rogers motor failure is NOT related to mine I can assure you of that, and should not be used for comparison here....Thank-You!

Kieth
If after teardown Eric cannot locate the reason for the failure the next thing would be to have the piston X-rayed to see if there were any casting flaws present. After that is becomes everyones best guess. The other motor that no one wants to talk about would be nice if they joined in to see if a true conclusion could be formed as to why it failed or maybe they already know why and are not talking.

Kieth
If after teardown Eric cannot locate the reason for the failure the next thing would be to have the piston X-rayed to see if there were any casting flaws present. After that is becomes everyones best guess. The other motor that no one wants to talk about would be nice if they joined in to see if a true conclusion could be formed as to why it failed or maybe they already know why and are not talking.

:exactly:

I have talked to the person in KY with the other failed piston. We discussed it over the phone and he has his theories on what happened. He was going to send me pictures of it for inspection, I hope he does. You cant tell everything from pics, but its a start. He only mentioned having an issue with one piston though.

Steve and I talked today for nearly an hour on these situations and we are both on the same page here. We want to know why this happened. I have a hard time believeing that relief cutting the pistons will cause them to weaken if its performed properly.

I'm not saying this to pick on anybody, but its no secret that Kyle has had more then a few motor issues over his career and thats to be expected, he has always been on the leading edge of making huge power. He is the only one I know of that has made a crankshaft into a two piece unit. I dont know his failures or the extent of them and its not really important, but saying he has had no problems is far fetched. I am sure that the billet rods have helped solve those issues though.

As for progress on Keiths motor, I've completed all the measurements on the top end as far as clearance measurements and such. Everything is dead on where it was when assembled.

Like Keith mentioned, Rogers motor failure has no similarities to Keiths. Its failure reason has been dislosed to Keith and a few others that have asked. It is not the topic of discussion here so I'm not going into it at this time. Once we get through this one, we can discuss Roger's if its that important.

I just got done building a new engine in importkilladmax's truck last week....as he had a piston crank in half on his original. His being a Lb7 is a little bit different. As for looking through the hole in the side of the block...you can clearly see where the piston is in two peices where it seperated at the pin. I know these are not LBZ's but seems very similar...Im gonna try and get through that engine next week to see exactly what happened. The rod looked to be fine..exept for coming loose from the piston and making a nice whole behind the starter pocket. I was able to find the pin digging around witha screwdriver and it is pretzeled from the piston. Just thought Id add to it.

Jeremy

Just had to post to help me keep track of this, interesting to see what the results will be. MMM PISTON'S!!!:)

I'm not at liberty to disclose the name of the person, but there is a motor in Cynthiana KY that just cracked 4 LBZ pistons and split one in two peices, there are several here on the board that know who I'm talking about.

Your truck Keith would make the second one that has split an LBZ piston, and it's undisclosed what happened to Rogers truck, whether it be split piston or something else.

Kyle Michael on the other hand has been running more boost, more fuel & more HP then anyone I can think of, with cut LB7 pistons and billet rods and hasn't had not one issue with the bottom end. Just some food for thought.

Have a good weekend.

Wade

Kyles results do not suprise me. What is different. His are cut to lower the compression ratio are they not? Not just for vavle clearence. As boost goes up compression ratio must go down. A buddies pulling tractor runs 80+psi of boost. His comp ratio is 15-1. These pistons could very well be being split by the forces of cylinder pressure. LBZ has a lower comp ratio but maybe not low enough?

Are pistons pins floating or pressed?

Are pistons pins floating or pressed?

Floating.

i know the guy in ky, he just had the engine rebuilt within the last six months before it went. It was only putting 600hp on the ground.

I'm not saying this to pick on anybody, but its no secret that Kyle has had more then a few motor issues over his career and thats to be expected, he has always been on the leading edge of making huge power. He is the only one I know of that has made a crankshaft into a two piece unit. I dont know his failures or the extent of them and its not really important, but saying he has had no problems is far fetched. I am sure that the billet rods have helped solve those issues though.

I have bent 24 rods and broke 1 crank(probably because of bent rods), and spun a main bering in the motor that housed the beta test of by 2 piece crank design(obviously), and also the first motor of 05(single turbo). The only way I finished the 05 season with the compound turbos was by basicly turning the whole top of the piston into a bowl which lowered the compression quite a bit. After 7 runs on those pistons in 05 I decided to run them and that block again in Climax in 06. I made over 20 runs in 06 and when I had the motor out for a cam change right before Stanford/Cynthiana Kentucky pulls they were still in great shape. After the run at cynthiana it was making new smells and noises, I have had a lack of time and motivation to get it pulled out since then. Mostly lack of motivation, Climax wasn't all pleasure this summer):h.

I do suspect piston issues. It ran leaner than it ever ran all summer, and I also had a nut brained idea to cut water back a little at the same time. I might just have to pull her in tommorrow and pull it apart.:rolleyes:

I think heat issues may have somthing to do with piston failures. I have ran a good amount of water....and always overfueled. I still think lean is mean.

Heat, Cylinder Pressure, Shear Force, Canadian Wiskey, or Kentucky Moonshine, whatever it may be, we are making a lot of power for stock components.

The good news is that at least we don't have headgasket problems, but then again that may be bad as they seem to work in a 5.9 as a safty relief.

Kyle

have you dynoed climax or your truck either one lately?

Kyle, thanks for clearing that up.

Have you any thoughts in running a forged piston in Climax? It seems that the stockers are holding up quite well for you? Perhaps the decrease in compression has helped that. You bring up a valid point on the heat possibly being an issue. Water has to help combat that.

I took some pics of a bunch of pistons tonite, I'm editing them for size and making sure they are clear and will post later. Pics of bad injectors, burnt pistons and some cracked pistons. I dont have any pics of Keiths pistons at this time as I have the head back on double checking some stuff, didnt feel like pulling it back off until I was done measuring.

Jon, dont you know that pull trucks dont dyno!):h


You need to change your sig Kyle :

"Member #1, 2 piece crankshaft Beta Tester":grd:

Ok so from what I understand here we now have 2 motors that have had cracked pistons that are cut (Myself and this motor in KY), and we have 2 motors that have cut pistons that are fine (Nick and Kyle). So what are we saying here?
It seems to me some are saying the pistons fail for various reasons....that I can understand. What I don't understand is how can we point the finger at any one thing going by the 4 trucks above. 2 have failed 2 have not.....if this is true then speculation is all we have and no facts. There is just not enough evidence to prove otherwise. There are very few motors in this "Catagory" to think otherwise. Am I wrong? :confused:

And I will say it again Rogers motor failure is NOT related to mine I can assure you of that, and should not be used for comparison here....Thank-You!

Keith, you mis-understand me. I'm not trying to point fingers here, I'm only trying to make a comparison for all of us to think about, I could care less who built your motor.

All I was trying to point out that maybe the LB7 pistons are soft enough to possibley absorb some of the shock of the higher HP levels. Maybe not, but this was not about pointing fingers, only about helping come up with a solution to the issue.

We should all continue to brainstorm this idea untill it's figured out, no reason for anyone to get thrown under a bus because of a leading edge failure. We just all have to learn from it and make it better.

Anyway, have a good night..............I've got beers to drink!!!

Kyle, thanks for clearing that up.

Have you any thoughts in running a forged piston in Climax? It seems that the stockers are holding up quite well for you? Perhaps the decrease in compression has helped that. You bring up a valid point on the heat possibly being an issue. Water has to help combat that.



I've had more than thoughts, I have dreams of beautiful new motor parts. I'm pretty sure I have had the image of shinny new pistons, blinging rods, all connected to a stroker crank you can see yourself in. The thoughts never end.

Truth is, Climax is an extreamly low budget project. Piston options will depend on what I find upon teardown. At this point I have confidence in the good ol lb7's.


Jon, I have not. I think it makes about 674.9hp

FWIW, I cracked a piston in one of my overheating LLY's. Not sure if that means anything, but thought I would share. Hard to see in this picture. The hole is evident, but which came first is undetermined.

I've had more than thoughts, I have dreams of beautiful new motor parts. I'm pretty sure I have had the image of shinny new pistons, blinging rods, all connected to a stroker crank you can see yourself in. The thoughts never end.


Your as pathetic as I am:eek: ):h

FWIW, I cracked a piston in one of my overheating LLY's. Not sure if that means anything, but thought I would share.
Rick, no offense, but if problemchild's pictures were 10's, yours are -10's. -:t :lol:

Ok so from what I understand here we now have 2 motors that have had cracked pistons that are cut (Myself and this motor in KY), and we have 2 motors that have cut pistons that are fine (Nick and Kyle). So what are we saying here?
It seems to me some are saying the pistons fail for various reasons....that I can understand. What I don't understand is how can we point the finger at any one thing going by the 4 trucks above. 2 have failed 2 have not.....if this is true then speculation is all we have and no facts. There is just not enough evidence to prove otherwise. There are very few motors in this "Catagory" to think otherwise. Am I wrong? :confused:

And I will say it again Rogers motor failure is NOT related to mine I can assure you of that, and should not be used for comparison here....Thank-You!

The issue to look at is that yours and the KY engine had similar machining done to lbz pistons. Wade, was just pointing out the possiblity that by decking off the top of lbz pistons MAY be a culpurit.

Nicks were cut differently and mine are lb7s.

I don't think he was pointing fingers, he was just pointing out similarities in failures.

How's this??

Pardon while a non-engineer posts:

If the pistons are cracking along the pin line, wouldn't that mean the opposite sides of the pistons are flexing under load? Could they be fighting the upward or downward movement of the rod?

If Rick's came from an overheating unit, then could the overheating have caused the piston to weaken, making it vulnerable to cracking like the higher HP ones have under "normal" (for high-HP) conditions?

Just floating ideas....

Rick, thanks, I knew you could do it.. LOL!

Interesting to see that its not cracked all the way across. I do notice the hole in the pistin in the bowl at the crack.. Looks like all the ones I have seen.

Kyle/Wade, Do you know what Cam is in XX's motor in KY? I never asked, reason I am curious is if he had to cut the pistons. I am not sure if he did or not.

Keiths pistons were flycut, but only a few, and just barely a few thou. This was only done to ensure that protrusion on all cylinders was equal. IIRC, Nick's pistons are also flycut for the same reason. I could be wrong on that, Steve may know more on that. That operation just takes a sliver off the top and almost seems insignificant.

I noticed in 6.6Dmax's pics that his pistons appear to be cut in just an X pattern. We are using a spot cutter on ours that is just a mm or so bigger then the valve head to clear.

Pardon while a non-engineer posts:

If the pistons are cracking along the pin line, wouldn't that mean the opposite sides of the pistons are flexing under load? Could they be fighting the upward or downward movement of the rod?

If Rick's came from an overheating unit, then could the overheating have caused the piston to weaken, making it vulnerable to cracking like the higher HP ones have under "normal" (for high-HP) conditions?

Just floating ideas....
except that i have cracked one also on my lly and it has never overheated in its life.

Guys,

How about lets drop the BS guessing on the metallurgies of the pistons in question, and send them to me for a real analysis. I can do hardness, microstructural (grain size and more), composition, and microscopic evaluation of the cracks. I are a metallurgist and do stuff like this for a living :)

How about for the good of the community, we do some real investigation and post the results here?

PM me for my address. I have used LB7 pistons already, just need a cracked LBZ piston to dissect.

I did this before for Eric on another issue and I think the results were beneficial.

OK, here are some pics I have of some piston failures. I dug these out of the aluminum barrel and cleaned a few up in the bead blaster for easy visual.

There are a bunch of pics, hope your dial up is working...

This piston appears to have had injector failure, I am not sure, but I think this piston had EDM'd injectors in it. Notice the erosion in it. Based on the casting numbers in the top, the pin is oriented from upper left to lower right as its seen here.
http://www.gmdieseltech.com/images/piston1.jpg

Here is the same pic from the side
http://www.gmdieseltech.com/images/piston2.jpg
Here is a pic of just plain and simple a melted piston. IIRC, this one was from a motor that had a history of injector failures, we were not expecting to see this, we tore the motor down for knocking lower end and found the main bearings spun, Second pic down is same piston from the side.

http://www.gmdieseltech.com/images/piston3.jpg
http://www.gmdieseltech.com/images/piston4.jpg

This piston is showing signs of erroding on the edge of the bowl, perhaps from an injector issue.
http://www.gmdieseltech.com/images/piston5.jpg

Another one with some serious errosion going on. Also appears it may have EDM'd injectors in it.
http://www.gmdieseltech.com/images/piston6.jpg

Another Piston with EDM'd injectors. I refer to these becuase the pattern being opposite each other is very typical of how EDM'd units are done when only 2 holes are cut.

http://www.gmdieseltech.com/images/piston7.jpg

Here is cracked piston. The position of the arrow at the right side of the piston indicates the pin is top to bottom as its shown in the pic. There is also signs of errosion. Its possible that this piston has EDM'd injectors as well.
http://www.gmdieseltech.com/images/piston9.jpg

Here is the same piston as seen from the bottom, you can see alot of damage down here as well.

http://www.gmdieseltech.com/images/piston10.jpg

Here is a cracked piston, again, across the pin. If you look carefully in the bowl, you can see the spray pattern, non of it lines up with the hole in the piston. That leads me to believe that the crack happened first and the hole was the escape for the fuel in the cylinder, crack likely left some sharp edges which developed into hot spots and thus the hole. One thing we have found very interesting was that on all the cracked pistons I can find, the hole is always on the same side of the piston, opposite the oiler passage. This piston is just about identical to what Keiths looks like
http://www.gmdieseltech.com/images/piston12.jpg


Same pic as above, pictured from below
http://www.gmdieseltech.com/images/piston13.jpg

ya...mine are cut across the whole piston...not a spot cut...makes em prettier...lol

Jeremy, not picking on how they were cut, just showing that there is at least two ways its been done. Both are just as effective IMO.

they worked for the little that it was run this year...who knows

it look like the star pattern is rather wide. this is in compared with the numerous of 71, 53, west buke diesel that i have done or been involed with rebuilding.
all of them iirc had a very tight star patern less than 1"-1.5" wide the one that rick put look closer the 3.25"-3.5" wide

the star pattern that rick put up has only nozle streem on top of the crack in the piston......the rest split evanly on booth side of the wrist pin. and crack like a titer toter with to much weight on booth ends.

ideal you want the streams to hit the center of the piston dome and ricocee out into the turn ups for better atomization.

basicly what i am trying to say here is the injection spray cone is to wide/large IMHO, thus lead to splitting the piston in half along the wrist pin by putting majority of the explosion on the outside of the piston instead of majority over the wrist pin.

Bu, thanks for changing the avatar.

You're pretty much dead wrong on how the spray should hit the bowl.

I say we take Mat up on his offer...send the LBZ piston to him for metalurgical tests, and compare to LB7 that he already did.

Mat, I'll send a piston your way, right now I have nothing to give up, but I'll get you something....

Bu, thanks for changing the avatar.

You're pretty much dead wrong on how the spray should hit the bowl.


i was just pointing something that i had notice and comparing to previous experiense in rebuilding diesels for the navy and pop testing countless of injectors. the only time i personally saw injection spray patterns that wide were on injectors on engine with bore of 8" or wider
i had to do a piston ispection on this engine with a boriscope the bore is 9 1/16" with a 10" stroke the pic that rick shown reminded me of the partern width wise that i saw in all 12 pistons
i wish i had pic of the cone spray so you could see it.
BTW the hammer is a 32oz stanely ball peen laying across 1 cylinder head. the other pic is the entire engine 20' long and 24,000# dry

pleae take this as an insult just a veiw from the other side of the apple.
honestly the internals of the dmax are new to me. since i have not had the privledge/oppertunity to tear one down

Well, Bu, sorry for being short.

I had an extended conversation with a PhD out of the Detroit area, did his study for a major auto company up there regarding diesel pistons and spray geometry.

The injector sprays a downward cone because this gives you the opportunity to break up the fuel. So rather than have one orifice pointing straight down (worst case), you can get the streams separated maximally if you use a down-facing cone.

Now within that cone, you have to do modeling with the expected fuel quantity to determine how many nozzle holes you want (and orifice size). This is why many have suggested going to more holes (like 10 instead of 7) to increase the flow and at the same time maintain small orifice sizes to get good atomization.

To burn the fuel most effectively, it should NOT strike the walls of the combustion bowl. This leads to formation of a "wall film" that does not burn well.

So, if you think about it, if you have the downward facing cone spray, then the inverted bowl keeps the volume small (to maintain high compression) yet allows the longest path from injector tip the bowl wall.

In other words, the chamber shape is the negative of what the spray cone looks like.

Anyone out there, correct me if I'm wrong, but there is a lot of brainpower being put to this....for emissions. I know that's different from making max HP, but you have to go through the same thought process to do either.

Well, Bu, sorry for being short.

I had an extended conversation with a PhD out of the Detroit area, did his study for a major auto company up there regarding diesel pistons and spray geometry.

The injector sprays a downward cone because this gives you the opportunity to break up the fuel. So rather than have one orifice pointing straight down (worst case), you can get the streams separated maximally if you use a down-facing cone. agreed

Now within that cone, you have to do modeling with the expected fuel quantity to determine how many nozzle holes you want (and orifice size). This is why many have suggested going to more holes (like 10 instead of 7) to increase the flow and at the same time maintain small orifice sizes to get good atomization. agreed

To burn the fuel most effectively, it should NOT strike the walls of the combustion bowl. This leads to formation of a "wall film" that does not burn well. agreed for the most part my sujestion to trighten the cone so that the parten was say an inch small in diameter then what it is normally. idealy bring more force to the top of the wrist pin vice hanging of the side of it and side loading the piston crown

So, if you think about it, if you have the downward facing cone spray, then the inverted bowl keeps the volume small (to maintain high compression) yet allows the longest path from injector tip the bowl wall.
i agree with this for the most part. as you stated the longest travel would be from the center of the piston plane to the outer parts of the inverted dome vise shooting it stright toward the edge of the inverted dome and barely touching the center of the piston were the power is transfered to the con rods. giving the explosion a higher mechanical advantage in spliting the piston. as you can see the initial flame front on those pistons is nowere near close to the piston center but more toward the out edge.

In other words, the chamber shape is the negative of what the spray cone looks like. agree to assist atomization

Anyone out there, correct me if I'm wrong, but there is a lot of brainpower being put to this....for emissions. I know that's different from making max HP, but you have to go through the same thought process to do either.
i agree there is a fine line that the Manufactors walk to try and meet the requirments and make as much resinable power with in those guidelines.
the more effeicint/completly the engine burn the fuel..... Nox goes up HC go down and CO stay about the same and when you decrease the effeicince level Nox decrease and HC increase


my experience is from running engine 90%-120% of the rating for 24/7 and doing the maintance and/or reparing them when they break. i believe the cone spray is to large for the application that it is in. if i had the means belive me i would test it.
it is the same reason why you want the spark plug on a gas engine as close to the center of the piston as possible, because that is were the flam front originates, to elimanate the side load on the piston

Guys,

How about lets drop the BS guessing on the metallurgies of the pistons in question, and send them to me for a real analysis. I can do hardness, microstructural (grain size and more), composition, and microscopic evaluation of the cracks. I are a metallurgist and do stuff like this for a living :)

How about for the good of the community, we do some real investigation and post the results here?

PM me for my address. I have used LB7 pistons already, just need a cracked LBZ piston to dissect.

I did this before for Eric on another issue and I think the results were beneficial.


Exactly what I was thinking "It's all in the microstructure" . By the way DONT clean the parts before you send them to him! Being in the same field I'd be interested in the pics.

Well, Malibu, we just disagree then.

A boat engine is a world apart from the Dmax.

One point you seem to be missing (or misstating) is that the center of the piston dome is NOT where the power is transferred to the wrist pin. It's out at the edges of the piston, at the bosses. There is nothing in the center of the piston except clearance for the connecting rod.

well i gues we agree to disagree....i am sure there is more to it then just what the piston are tell.

on the other hand i am looking forward to see what you in you testing and comparison of the pistons

Bu, if the pressure is the same everywhere in the bowl (which it pretty much has to be), how do you come up with this "side loading" thing?

That makes no sense to me right now.

Some of the pics are pistons that have burnt from being too hot. (EGT) nothing to do with bad injectors. I tend to agree with Malibu to some extent. The majority of the fuel should be injected into the bowel of the piston. Some of the pictures clearly show fuel being spray across the top of the piston. Probably from advanced timing. Spray angle of the nozzle could be changed but would require new nozzles. More holes would be ideal but you really decrease the strength of the tip , especially at the rates of fuel that is being injected. The tip can be blown off easier with more holes in it. Another thing that could possibly done is increase the injector tip protrusion into the combustion chamber. Just remember the flames that are being created. Like a blow torch in this pic: ( Low pressure compared to Dmax)

Some of the pics are pistons that have burnt from being too hot. (EGT) nothing to do with bad injectors. I tend to agree with Malibu to some extent. The majority of the fuel should be injected into the bowel of the piston. Some of the pictures clearly show fuel being spray across the top of the piston. Probably from advanced timing. Spray angle of the nozzle could be changed but would require new nozzles. More holes would be ideal but you really decrease the strength of the tip , especially at the rates of fuel that is being injected. The tip can be blown off easier with more holes in it. Another thing that could possibly done is increase the injector tip protrusion into the combustion chamber. Just remember the flames that are being created. Like a blow torch in this pic: ( Low pressure compared to Dmax)
We started playing with that a year ago, dropping the injector further by using a thinner copper washer at the bottom. We can only go so far before the top of the injector bottoms out on the head though. Not sure how well its worked yet, hard to see inside with out tearing down motor

I agree with you guys if you're talking a couple degrees more down angle, but certainly not as much as Malibu is suggesting. Too much would likely burn a hole in the dome.

Bu, if the pressure is the same everywhere in the bowl (which it pretty much has to be), how do you come up with this "side loading" thing?

That makes no sense to me right now.

Some of the pics are pistons that have burnt from being too hot. (EGT) nothing to do with bad injectors. I tend to agree with Malibu to some extent. The majority of the fuel should be injected into the bowel of the piston. Some of the pictures clearly show fuel being spray across the top of the piston. Probably from advanced timing. Spray angle of the nozzle could be changed but would require new nozzles. More holes would be ideal but you really decrease the strength of the tip , especially at the rates of fuel that is being injected. The tip can be blown off easier with more holes in it. Another thing that could possibly done is increase the injector tip protrusion into the combustion chamber. Just remember the flames that are being created. Like a blow torch in this pic: ( Low pressure compared to Dmax)


side loading was the only termaknowledgy i could think of.
i am sure the you know how metel expands. piston are not 100% cylindrecal(sp) the crown is smaller in dia than the piston skirt. roughly from .0001"-.001" and even more so as the piston gets larger in dia
another thing to keep in mind is when the explosion occures everything flexes inside. the bore walls will grow a couple .001"in dia and the piston crown will flex outward to meet the bore wall.

as diesel pro stated that same thing i noticed the about the flame path going across the top of the piston and said it was rather wide. this would cause exsessive stress on the center of the piston(center line directly above the wrist pin) in trying to split the piston in half like a cord of word.

another thing i saw was everytime the piston cracked the left side of the piston crack first then spread to the right side. in each instance there are two injection stream spliting the wrist pin also directly over the melted area.
now why is it melting IDK but i believe it is spliting in direct result of the flame front being to wide and pulling the piston apart.....starting at the melted spot

as for the melting IDK why, maybe diesel pro is on to something with there being to much advance timing i dont have any reason why.... my specualtion would be that the melting flow in relation to how hot the piston got starting at the center ledge and working outward then once that (bridge?) the metal over the wrist pin got soft enough form the heat the pressure pulled the piston apart

hopefully i put that together well enough to make some sense out of it... my verbale and writing skills arent that great.

I agree with you guys if you're talking a couple degrees more down angle, but certainly not as much as Malibu is suggesting. Too much would likely burn a hole in the dome.

i am not sugjesting a major change maybe like 5-10% narower/tighter

sorry i should have been clearer on that point

Mat and Malibu:

Regardless of your small differences in opinion, its a breath of fresh air to see the two of you discussing it professionally. Thanks for the excellent contributions

I get no respect.

To get more protrusion you could counter bore the injector nut down a little on the inside or counter bore the head deeper. Would it help? Who knows.

I would like to also thank DieselPro for accepting he was left out on accident...):h

My wife made me take all my meds today :mad:



:lol:

My wife made me take all my meds today :mad:



:lol:


or did she make sure all your nuts and bolt were tight;)





:lol:

):h no comment about this morning :D

Eric, I could dig for it, but what's the GM clearance spec between the top of the piston and the head deck?

I remember reading that A/B/C gasket sets are offered based on the protrusion height.

I'm not sure how to read the spray marks on the very top of the piston....is it due to excessive timing advance, or is it just spillover from what comes back out of the hat?

In a stock application I believe the intent is to not have the liquid stream hit the bowl. In modded apps, especially with overbored injectors, I'd bet money it hits big time and who knows where it goes from there. Trouble is, most folk running over injectors also have timing, so it'd be hard to separate the effects.

This is why more holes are better, at least in my mind.

I do know a 24V Dodge guy who blew the tip off an injector, but I have no idea how good the nozzles were in the first place, % over, or anything. The motor apparently puked it out since they didn't find it. Truck started running wierd, started smoking pretty good, but ran. Once they shut it off, it would not restart.

I dunno if Cummins nozzles of that gen are weaker design/metallurgy. I assume they're a whole different animal anyway. Our injector tips are damn hard, definitely a tool steel, but that may be nothing new. I have one that I cut, sectioned, and polished parallel to one orifice so I could get a good side-view.

Mat, protrusion is usually 8-12 thou. A B C gaskests are .038, .040, .042 respectively.

OK, so if the protrusion is 0.012", you use the C gasket and you'd have an 0.030" gap in there.

Maybe that's enough to let some of the spray marks from overfueling "bleed" onto the top of the piston. Dunno.

I'm sure someone has already done it, but if you sat down with some trig, and knowing the injector protrusion and dimensions, you could figure out at what advance the spray would be on top of the piston or within the bowl, eh?

Mat, yes. I only use the C's anymore, its always a safe bet and its easier to stock 2 part numbers (L and R) then 6.

As for the trig, If I knew the spray pattern, I would have done it already. I have Keiths motor mocked here with the degree wheel on it.

I believe I measured the angle. It's at work, used an image analysis program to measure it.

If I can get the pic in usable format I'll send it to someone who can host it.

On edit, the nozzle I whacked up was a LB7 nozzle. If any of y'all liLLY guys want to donate a nozzle to science, I'll hack it up too.

Real time chat in the Lounge right now....I'm there..

Real time chat in the Lounge right now....I'm there..
it wont load or i would join you


anothing would be to see a piston out of an engine that has not been altered to she you the injection mark are on it

yeah I'm having unexpected java issues...

got hundreds of them..

norton blosck the pop ups

wow I love good tech reading. LOL most everything I was going to contribute has already been said......damn I hate that.

Thers's a sticky in forum ops about lounge issues.

Thers's a sticky in forum ops about lounge issues.
:thankyou2

:thumb:

I would like to add something to this discussion. I would assume that the spray pattern that was seen on Rick's pistons was because the pulse width of the tuning was increased thus hanging the injector open longer and taking the spray pattern out of the bowl of the piston. That's why it's better to run larger injectors and shorter pulse width because you can get the same amount of fuel into the cylinder without taking it outside the bowl of the piston.

That's also why all you gentlemen running EFI live with stock injectors and making big power should use caution, the fuel that your adding could very well be spraying not only outside the bowl but could be washing your cylinder walls aswell.

That "Wide" spray pattern is commonly seen by GM as a "Power Adder" motor and will not warranty failure if it's found.

Just my .02 take it for what it's worth.

Cheers,
Wade

I would assume that the spray pattern that was seen on Rick's pistons was because the pulse width of the tuning was increased thus hanging the injector open longer and taking the spray pattern out of the bowl of the piston. That's why it's better to run larger injectors and shorter pulse width because you can get the same amount of fuel into the cylinder without taking it outside the bowl of the piston.
Cheers,
Wade

I'll second that. Or timing to advanced.

I would like to add something to this discussion. I would assume that the spray pattern that was seen on Rick's pistons was because the pulse width of the tuning was increased thus hanging the injector open longer and taking the spray pattern out of the bowl of the piston. That's why it's better to run larger injectors and shorter pulse width because you can get the same amount of fuel into the cylinder without taking it outside the bowl of the piston.

That's also why all you gentlemen running EFI live with stock injectors and making big power should use caution, the fuel that your adding could very well be spraying not only outside the bowl but could be washing your cylinder walls aswell.

That "Wide" spray pattern is commonly seen by GM as a "Power Adder" motor and will not warranty failure if it's found.

Just my .02 take it for what it's worth.

Cheers,
Wade

So stock injectors are to blame. Interesting considering it did not have stock injectors in it.

And your point that EFILive tunes are somehow "magical" holds no water either. All "500hp Class" tunes have similiar timing and duration. The dyno tells everyone what is needed, and when you stray, you lose power. No timing, no duration, no power.

Do you want a picture of the "star pattern" on a piston from an engine that was test run at GM prior to delivery to the assembly line? I have an engine that was freight damaged on it's way to the assembly plant and sold at auction. Imagine my surprise when the pistons had the star pattern on them. Perhaps GM is doing their engine testing with a 500hp tune.

Eric and Rick, thanks for the pictures. :cool:

I would like to add something to this discussion. I would assume that the spray pattern that was seen on Rick's pistons was because the pulse width of the tuning was increased thus hanging the injector open longer and taking the spray pattern out of the bowl of the piston. That's why it's better to run larger injectors and shorter pulse width because you can get the same amount of fuel into the cylinder without taking it outside the bowl of the piston.

That's also why all you gentlemen running EFI live with stock injectors and making big power should use caution, the fuel that your adding could very well be spraying not only outside the bowl but could be washing your cylinder walls aswell.

That "Wide" spray pattern is commonly seen by GM as a "Power Adder" motor and will not warranty failure if it's found.

Just my .02 take it for what it's worth.

Cheers,
Wade



John Coe's Piston:
http://www.gmdieseltech.com/images/piston12.jpg

Do you want a picture of the "star pattern" on a piston from an engine that was test run at GM prior to delivery to the assembly line? I have an engine that was freight damaged on it's way to the assembly plant and sold at auction. Imagine my surprise when the pistons had the star pattern on them. Perhaps GM is doing their engine testing with a 500hp tune.

This is why it's my opinion that the patterns oberved are only part of the whole picture. I don't think we should rush to judgement about what the pattern is or isn't saying.

In time I think we'll come to a better understanding of this, but we're not there yet.

That's also why all you gentlemen running EFI live with stock injectors and making big power should use caution, the fuel that your adding could very well be spraying not only outside the bowl but could be washing your cylinder walls aswell.

I don't see this as a problem simply because overfueling it usually happens on the combustion stroke. As far as washing the cylinder walls if combustion has already started then washing them down is impossible. Now washing them down is possible with too much timing on the compression stoke, this is where bursting can be caused.

I would like to add something to this discussion. I would assume that the spray pattern that was seen on Rick's pistons was because the pulse width of the tuning was increased thus hanging the injector open longer and taking the spray pattern out of the bowl of the piston. That's why it's better to run larger injectors and shorter pulse width because you can get the same amount of fuel into the cylinder without taking it outside the bowl of the piston.

That's also why all you gentlemen running EFI live with stock injectors and making big power should use caution, the fuel that your adding could very well be spraying not only outside the bowl but could be washing your cylinder walls aswell.

That "Wide" spray pattern is commonly seen by GM as a "Power Adder" motor and will not warranty failure if it's found.

Just my .02 take it for what it's worth.

Cheers,
Wade

So stock injectors are to blame. Interesting considering it did not have stock injectors in it.

And your point that EFILive tunes are somehow "magical" holds no water either. All "500hp Class" tunes have similiar timing and duration. The dyno tells everyone what is needed, and when you stray, you lose power. No timing, no duration, no power.

Do you want a picture of the "star pattern" on a piston from an engine that was test run at GM prior to delivery to the assembly line? I have an engine that was freight damaged on it's way to the assembly plant and sold at auction. Imagine my surprise when the pistons had the star pattern on them. Perhaps GM is doing their engine testing with a 500hp tune.

As Pat said a stock engine when torn can show the star pattern. Wade you opened a can of worms on this one. While I do agree with you in part. I also believe that big injectors are more of a risk for washing down the cylinders. Here is the trouble. A 50% injector has holes that are 50% bigger correct? The bigger injector does not flow 50% more across the broad. I am willing to bet its flow curve is vastly different. On a street truck this means custom tuning. Because of the increase in flow the lower fuel settings and pilot injection will need to be reduced. Letting it idle for any length of time could create wash down. I think that this would be are far greater risk for cylinder wash then say running a big pulse a WOT of ten seconds. To really make bigger injectors work we need to custom tune them for a street driven truck. But with out flow data it will be hard to get the lower settings adjusted properly. I do agree that getting the shot in quicker would defiantly be a good thing. But running big injectors with stock or "Canned" tuning is a far greater risk to wash the cylinders IMHO.

Also I still think that the main issue with a lot of these failures is too high of a compression ratio for the boost levels. If you want to say 60+psi. of boost on a street driven truck I think you should be running a lower compression ratio than even the LBZ pistons provide.

Also I still think that the main issue with a lot of these failures is too high of a compression ratio for the boost levels. If you want to say 60+psi. of boost on a street driven truck I think you should be running a lower compression ratio than even the LBZ pistons provide.

Much lower compression than the LBZ piston provides and Kieth will have to install either injection as a starting agent.:eek:

Until Eric measures everything we have no idea what the compression ratio in Kieth's motor was/is. Yes, they started with LBZ pistons but where did they end up after valve pockets and reworked heads.............. no one knows at this time.

Eric Have you been able to snap some pics of NG disassembled.

Here is a piston from an engine that was only test run at the factory. If I touch the piston, the carbon wipes off with my finger, it's a very thin coat.

So stock injectors are to blame. Interesting considering it did not have stock injectors in it.

And your point that EFILive tunes are somehow "magical" holds no water either. All "500hp Class" tunes have similiar timing and duration. The dyno tells everyone what is needed, and when you stray, you lose power. No timing, no duration, no power.

Do you want a picture of the "star pattern" on a piston from an engine that was test run at GM prior to delivery to the assembly line? I have an engine that was freight damaged on it's way to the assembly plant and sold at auction. Imagine my surprise when the pistons had the star pattern on them. Perhaps GM is doing their engine testing with a 500hp tune.

Pat, no need to get angry or aggressive here, I never said that what you are doing is bad, I made a very general statement to the public to be careful if they are tuning their truck to watch how much pulse width they are putting into the tune. And maybe I shouldn't have used cylinder washing, I should have used cylinder TORCHING!!!

And the larger star pattern is not something I just came up with, it's a GM TSB I read a while ago to inform the GM techs that were diagnosing a motor failure to look for. Anytime that you put a chip or programmer on a truck that opens up the pulse width you will also inlarge the spray pattern on the piston over stock.

Anyhoo, with stock injectors to get the same amount of fuel you are extending the pulse width waaay out to get the same amount of fuel that a larger injector can get in a short amount of time. My personal opinion (Its just that) is to go with a high quality larger injector nozzle and lower the pulse width and tune the truck with bigger inject's. That way you can get the extra fuel that you need/want and keep the explosion in the piston bowl where it needs to be. In no way do I think that mild tuning is doing anything serious to our motors, but if your shooting for 600-700HP I would personally do it with bigger injects.

Just my .02, Flame away.

Cheers,
Wade

Guys, the attachment provided is a compression ration calculator I originally wrote in 1982. I adapted it to Excel for my sales staff to use when I owned part of Air Flow Research. (VP of Engineering and Manufacturing).

I offer it to all Diesel Place members to use, copy, redistribute and claim as your own as you see fit. :D

"Deck to piston clearance" assumes a positive number if the piston is in the hole below the deck at TDC. A negative number is assumed if the piston is above the deck at TDC.

You can also use it to calculate the volume of the head gasket by entering in the bore of the "gasket" and use the thickness value of the gasket as the "stroke".

Enter # of cyls as 1. The resulting gasket volume will be listed in CID, multiply this value by 16.39 to obtain "CCs".

Additionally you may use the formula to calculate the volume of a valve pocket in the same fashion as a gasket, assuming it is a completely round pocket.

Enjoy! Compliments of SoCal Diesel. :D

GM 6.5L Turbo pistons have no steel insert. They are hard anodized on top and in the ring area.

All 6.5 turbo pistons have the steel plate in them...

Pat, no need to get angry or aggressive here, I never said that what you are doing is bad, I made a very general statement to the public to be careful if they are tuning their truck to watch how much pulse width they are putting into the tune. And maybe I shouldn't have used cylinder washing, I should have used cylinder TORCHING!!!

And the larger star pattern is not something I just came up with, it's a GM TSB I read a while ago to inform the GM techs that were diagnosing a motor failure to look for. Anytime that you put a chip or programmer on a truck that opens up the pulse width you will also inlarge the spray pattern on the piston over stock.

Anyhoo, with stock injectors to get the same amount of fuel you are extending the pulse width waaay out to get the same amount of fuel that a larger injector can get in a short amount of time. My personal opinion (Its just that) is to go with a high quality larger injector nozzle and lower the pulse width and tune the truck with bigger inject's. That way you can get the extra fuel that you need/want and keep the explosion in the piston bowl where it needs to be. In no way do I think that mild tuning is doing anything serious to our motors, but if your shooting for 600-700HP I would personally do it with bigger injects.

Just my .02, Flame away.

Cheers,
Wade

I'm not angry, I just don't want readers to associate running stock injectors with engine failure without any data to support it.

Things have changed alot in the last year. Common sense does indicate that big injectors would make sense. However the test data isn't supporting it yet, which surprises me at least as much as anyone else. Remember we were told the LLY injectors flow less (true), and could never support over 400hp (false). Then we were told an LLY could never match "tuning only" power of a LB7 due once more to the tiny LLY injectors (false again).

Nobody knows what the stock injectors will support as far as HP goes, nor do we know that big injectors will "save" your engine. Seems many racing failures have been using big sticks, BUT that is not fair. A high percentage of the $$$ buildups are using big injectors, so until there are lots of stock injector big HP engines out there, we cannot compare fairly. So far all the trucks I have tuned with the stock sticks have survived, and several are over 650hp.

There are 3 possible scenarios:

1) Injectors have no effect on piston life.
2) Small injectors hurt pistons.
3) Big injectors hurt pistons.

The only engine failure with one of my customers that I know of was a big stick truck, but I do not believe it was injector related. It was a head gasket issue.

As Pat said a stock engine when torn can show the star pattern. Wade you opened a can of worms on this one. While I do agree with you in part. I also believe that big injectors are more of a risk for washing down the cylinders. Here is the trouble. A 50% injector has holes that are 50% bigger correct? The bigger injector does not flow 50% more across the broad. I am willing to bet its flow curve is vastly different. On a street truck this means custom tuning. Because of the increase in flow the lower fuel settings and pilot injection will need to be reduced. Letting it idle for any length of time could create wash down. I think that this would be are far greater risk for cylinder wash then say running a big pulse a WOT of ten seconds. To really make bigger injectors work we need to custom tune them for a street driven truck. But with out flow data it will be hard to get the lower settings adjusted properly. I do agree that getting the shot in quicker would defiantly be a good thing. But running big injectors with stock or "Canned" tuning is a far greater risk to wash the cylinders IMHO.

Also I still think that the main issue with a lot of these failures is too high of a compression ratio for the boost levels. If you want to say 60+psi. of boost on a street driven truck I think you should be running a lower compression ratio than even the LBZ pistons provide.

I agree with you JB, I don't think that stock injectors caused the failures here, but I think that the issue may largely be caused by having your cake and eating it too. If you want massive HP and daily driveability there is going to be a line where you won't be able to do both on #2 only. Something has to give, if you want huge boost then your going to have to lower the compression ratio to compensate for that, now how much boost and how low you need to take the compression will affect whether or not you will need to ether start your truck on a cold day or if it just fires right up.

We are all breaking new ground here and who knew when the pistons would start to fail, I think that these disscussions are great to improve the performance of these trucks, and I hope that no one here thinks that I'm trying to bust anyone's balls, I'm only trying to help.

Cheers,
wade

Much lower compression than the LBZ piston provides and Kieth will have to install either injection as a starting agent.:eek:

I know a 15:1 pulling tractor that will start right on a 50 deg day. What does that have to do with a Dmax? Not much. :) 16:1 should be fine. What does Kyle run? His starts just fine.

I thought I read somewhere in this thread that Kyle was using LB7 pistons.

I agree with you JB, I don't think that stock injectors caused the failures here, but I think that the issue may largely be caused by having your cake and eating it too. If you want massive HP and daily driveability there is going to be a line where you won't be able to do both on #2 only. Something has to give, if you want huge boost then your going to have to lower the compression ratio to compensate for that, now how much boost and how low you need to take the compression will affect whether or not you will need to ether start your truck on a cold day or if it just fires right up.

We are all breaking new ground here and who knew when the pistons would start to fail, I think that these disscussions are great to improve the performance of these trucks, and I hope that no one here thinks that I'm trying to bust anyone's balls, I'm only trying to help.

Cheers,
wade


Point well said! I do agree. At what compression is street ability is not there anymore? Where that is only time will tell. This thread has great info on it. I am struggling right know with what to do in my motor build. Forged pistons sound great but I really do not want be tearing my motor down once or twice a year just to check them for ring groove wear. Also the lack of oil passage to cool them concerns me. LBZ pistons also sound good but several things worry me about them. Until I can get my hands on one to dissect I will not pass judgment. What concerns me is if the internal oil passage is the same as the LB7 pistons and in the same location then I can see why they are splitting. The distance from the pin bushing bore to the passage will only be around .125. If my hunch is right they are actually spliting from the pin bore up. Right know I am leaning toward cutting (turning) old LB7 pistons.

John

I thought I read somewhere in this thread that Kyle was using LB7 pistons.


Sorry about that. He runs cut LB7 pistons. I meant to say. What compression ratio does he run? He runs more boost now than I want to and makes it work. So knowing what he runs would be real useful info.

JB

If it was a piston issue then why do we have LB7 pistons with the exact crack in the same place as Kieth's motor? Why is Nick's motor going fine at 10K miles and counting. There is something else going on that has not yet been found or at least not discussed here.

Here is a piston from an engine that was only test run at the factory. If I touch the piston, the carbon wipes off with my finger, it's a very thin coat.

This is what I've seen on stock pistons (as I'm sure many have).

I think it's reasonable to expect that this is "bleed" from the normal burn process (while the piston is on its way down).

I'm not sure the marks in and of themselves will tell us much. I bet that appearance exists at all kinds of fueling rates, but I'll need one of Eric's barbequed pieces to know for sure.

Could the wider pattern be caused by pilot injection?

Just thinking out loud.

I don't see why not.

We just need someone with a stock truck to take their heads off, polish their pistons, then put it all back together for a month and run an EFI tune with the PI turned off. Then take it all apart again to shoot some pictures for your web buddies.

That's not too much to ask, is it?

):h

Sounds like a good job for McRat, he has all kinds of testing time...

Could the wider pattern be caused by pilot injection?

Just thinking out loud.

Perhaps. Or when starting, the CP3 is "full blast", and possibly the injector duration is large relative to such a low RPM to get it lit.

I don't see why not.

We just need someone with a stock truck to take their heads off, polish their pistons, then put it all back together for a month and run an EFI tune with the PI turned off. Then take it all apart again to shoot some pictures for your web buddies.

That's not too much to ask, is it?

):h

Sounds like a good job for McRat, he has all kinds of testing time...


I don't think so,I agree. The way he swaps turbos, heads will be a walk in the park for Pat after the first time! :)

Here is a piston out of a new motor. As you can see there is only the run time that was done at the engine plant to qualify the motor as being good. While it doesn't show a lot it does show that the factory testing puts the pattern in place on the piston top as well as the bowl. This motor was never installed in a truck or run. You can see that none of it hits the outer edge of the piston.

the patern is not as wide as the ones that eric posted

i put eric and deisel tech pics on this. that star parten is def larger on the melted ones

Miles, rpm, and load alone could have widened the pattern from a no load comparison.

JB

If it was a piston issue then why do we have LB7 pistons with the exact crack in the same place as Kieth's motor? Why is Nick's motor going fine at 10K miles and counting. There is something else going on that has not yet been found or at least not discussed here.


Steve

I think it is a cylinder pressure issue. I understand that both have types have had failures. I a still sticking to the excessive cylinder pressures are caused by to high boost for the comp. ratio. I think that LB7 piston is a better canidate to be cut then the LBZ piston. I can not prove it till I get my grubby little hands one though. I have a hunch. As for Nicks motor. I do not know. But from what I have read he is running mid 60s for peak boost where Keith was in the mid 70s. But others have broke at less then both of those. Another thing we need to think about is that these are castings. Material strenght form peice to peice is not near as constant as say a forging or a billet. Also that being a casting means they are brittle when compared to a forging. This meets that one piston may fail another would have lived. This to big a gamble for me. That is why I thinking Low compression cut LB7 pistons. Let the turbo do the work, and keep the cylinder pressures in check.

JB

All this talk about fighting cylinder psi makes me wonder who is keeping track of it? How do you eliminate something you are not monitoring?

All this talk about fighting cylinder psi makes me wonder who is keeping track of it? How do you eliminate something you are not monitoring?
:hail: I agree... Speculate 'til the cows come home - it'll never be any more than speculation unless somebody actually manages to monitor these 'X' values & duplicate the problem at the same time...

All this talk about fighting cylinder psi makes me wonder who is keeping track of it? How do you eliminate something you are not monitoring?

Easy!

Just put a piston in a hyd press, and dial it up till it breaks.

Write down that number.

That number on the paper is too damn much pressure. :D

The power output of Nick's motor and Kieth's motor are near identical. To make power you must make cylinder pressure. Sure each can be done a little different but I bet they are close to the same. Now done wrong cylinder pressure sky rockets for very little to no gain in power. Do it bad enough and it cost power. We will never know on this motor as its apart but let's look at the big picture. LB7's crack, LBZ's crack. The LBZ casting was strengthen by GM and lower compression ratio to start with. Why would you start with an LB7 unless you have plenty of them lying around. Now casting differences are going to be there by the same amount in both cases. So maybe the best bet is to check any casting prior to reworking it. Nick's were off the shelf unchecked parts as were Kieth's. A X-ray of Kieth cracked piston will show if there are any voids that could have weakened the piston but we would need to have something to compare it to to see any differences and I do not think Nick would let me tear his back apart so we could check his. So if all 8 of Kieth's were check and found to all be the same, common sense would tell us the problem is elsewhere. If machining of the piston is at fault then you should be able to see that, but since no one but Eric has seen the piston in question he would need to make that call.

...To make power you must make cylinder pressure. Sure each can be done a little different but I bet they are close to the same. Now done wrong cylinder pressure sky rockets for very little to no gain in power. Do it bad enough and it cost power....
Doesn't Statement 'B' kinda contradict Statement 'A'????? :confused:

High cylinder pressure at the wrong time cost power and breaks pieces, cylinder pressure that is a quick spike dropping to little to nothing will hurt parts but make OK power. Cylinder pressure that ramps up quick holds and drops slowly makes big power and is as good as it gets on parts. You need to look at it like a cliff or a rolling hill. If the cliff is before the piston reaches TDC pressure is too high at the wrong time = Bad, if the cliff is ATDC it makes power but will still hurt parts if it gets too high. Now the rolling hill at the right time keeps the average pressure up in the cylinder and makes good power and is much nicer to parts but is down some power from the more cliff like pressure rise. It tricky to get it right but your better off down a little power to save parts if you want something that's going to last a long time. Where as in racing we tend to push it closer to a cliff on the rise time and try to keep the average pressure up. Sure it wears parts out faster but it sure runs good. I hope that all makes sense to you.

Yes?

All this talk about fighting cylinder psi makes me wonder who is keeping track of it? How do you eliminate something you are not monitoring?

Amen. I know a couple people have the necessary probes, but I assume the info is pretty much kept under wraps.

Easy!

Just put a piston in a hyd press, and dial it up till it breaks.

Write down that number.

That number on the paper is too damn much pressure. :D


Fred Flintstone, P.E., consulting engineer ):h

x2

Amen. I know a couple people have the necessary probes, but I assume the info is pretty much kept under wraps.


The probes are the cheap part. Try the data logging equipment and amplifiers. Then you will understand why the information isn't given out freely. It cost lots of money to learn from the instruments so it needs to be paid for somehow.

Uh, warp speed sampling rate, eh, Captain Zulu?

Knowing that the LB7 pistons do crack as well it seems the LBZ. The LBZ pistons have been used quite a few builds and have there are some that have seen failure.
Just thinking would the longer wrist pin in the LBZ pistons be expanding at a different rate then the LB7 due to the heat?? I have read there are bushing in the LBZ, and it may have been stated already, but just wondering if the longer pin may be expanding just enough to cause the piston to crack, under hotter conditions?? Just a thought..
Jon

I believe the pin is free to float axially, so any lengthwise expansion would not seem to matter IMHO.

Just the extra metal from the length would be expanding from the heat at a slightly different rate then the shorter LB7 with less mass... I was thinking more on the lines of expanding diameter versus axially.. The way it is looking of some of these pistons spliting the way they are....
Just thinking out load..
Jon

I don't think so. Thermal expansion is pretty linear, so when you say "a slightly different rate," that's not really possible as far as I know.

If you mean that the pin will heat more slowly than a shorter one due to the increased mass, then that's correct, but I think on a percentage basis the differences are small. Do the math and check me.

Thermal expansion in the radial direction would be the same as with a shorter pin. If the pin boss is made to cover the pin length, then the unit pressures (force per area) would be the same.

as stated....keiths and nicks engines are built about the same...but the tuning is different...now i know you guys are saying the tuning probly has nothing to do with it...but wasnt Nicks truck tuned quickly and might not be as radical as keiths...now i know only steve and or nick nows the truth..but could that be some of it...i know bobo was probly going balls deep when he tuned keiths rig??

as stated....keiths and nicks engines are built about the same...but the tuning is different...now i know you guys are saying the tuning probly has nothing to do with it...but wasnt Nicks truck tuned quickly and might not be as radical as keiths...now i know only steve and or nick nows the truth..but could that be some of it...i know bobo was probly going balls deep when he tuned keiths rig??


That is exactly what I was thinking.

A X-ray of Kieth cracked piston will show if there are any voids that could have weakened the piston but we would need to have something to compare it to to see any differences and I do not think Nick would let me tear his back apart so we could check his.

Doubtful, but everything has a price:D

Steve hasn't tuned on mine since the motor passed its 500mi mark. I'm confident he'll get more power out of it. how much nobody knows but its made 675 before. i think Keith was right around that same # but only he would know that.

as stated....keiths and nicks engines are built about the same...but the tuning is different...now i know you guys are saying the tuning probly has nothing to do with it...but wasnt Nicks truck tuned quickly and might not be as radical as keiths...now i know only steve and or nick nows the truth..but could that be some of it...i know bobo was probly going balls deep when he tuned keiths rig??

as stated....keiths and nicks engines are built about the same...but the tuning is different...now i know you guys are saying the tuning probly has nothing to do with it...but wasnt Nicks truck tuned quickly and might not be as radical as keiths...now i know only steve and or nick nows the truth..but could that be some of it...i know bobo was probly going balls deep when he tuned keiths rig??


It was a very mild tune. They were going slow

Eric hasn't chimed in for a little bit... Any news to fuel another 2 days' speculation from the peanut gallery?

I have the motor down for inspection. Pics have been taken and I have sent them to Keith. After he reviews them, I will post the pics. I have shots of the piston, bearings and cylinder walls.

again, the more hp we produce the more failures we will see. And yes of course tunning is responsible. the bigger tune the more failures we will see. just because we dyno, that does not mean there are no spikes in the hp or the resistance, such as a bounce from wheel hop. I think that this is a good discussion but the end result is the same we need stronger pistons. Then once we have that, we will need some other part made stronger...

It would appear the best way to get a "substantially" stronger piston is to more the wrist pin hole down in the piston, giving more material on top of the wrist pin. Unfortunately this would require shorter rods.:( Probably not a good trade off.

shorter rods taller pistons, hopefully same rotating mass.

Getting shorter rods to clear will be a PITA! This is not going to be easy!

shorter rods will reduce the torque.then we will need more hp.

Getting shorter rods to clear will be a PITA! This is not going to be easy!

Shorter rods is very simple and cheap.

Normally it only takes a 2-stage nitrous system. ;)

shorter rods with larger pistons would also create other problems such as higher stresses on the pins and crank.

I've got a full set of shorter rods for anyone that would like to try some!! ):h ):h

shorter seem to be the "In" fashion these days!

Has anybody tried playing with shape?

I've got a shorter rod for anyone that would like to try some!! ):h ):h

:eek: :eek: -:t

Owned!!:lol:

Which shape would you like, we have several different shapes and colors. Event have some of the latest designed 3 piece rods.

:eek: :eek: -:t

Ok, I must admitt that was a pretty good one!!! ):h ):h

Which shape would you like, we have several different shapes and colors. Event have some of the latest designed 3 piece rods.

:funnypost

already having to machine off a smidge on the crowers to clear counter weight ...don't think shorter will work....but hell...who needs counter weights...

Jeremy

Which shape would you like, we have several different shapes and colors. Event have some of the latest designed 3 piece rods.
):h Sign me up!

Actually I was talking about the shape & design of the piston bowl... Or were we just looking at pictures of spray patterns for fun?

You should know this group Wade ;) If I didnt hack your comment up you know Scott would have ):h All in fun pal :)

Here is a piston out of a new motor. As you can see there is only the run time that was done at the engine plant to qualify the motor as being good. While it doesn't show a lot it does show that the factory testing puts the pattern in place on the piston top as well as the bowl. This motor was never installed in a truck or run. You can see that none of it hits the outer edge of the piston.


This is proper by ALL accounts. The JWI ( jet wall impact ) is perfect. Wide JWI is an old trick on CR engines to lower emissive constituents.

Remember guys, that the mass of the fuel is injected as a liquid but mostly from droplet collision. The wall impact breaks the stream and collided droplets back apart for faster vaporization. Uncollided droplets are always present on the periphery or outer boundry of the spray. They never make it to the cylinder wall before ignition. It is simply too hot.

I sectioned an LB7 piston today and thought some of you might like to take a look. First, I baloney-sliced it down one of the ring grooves. I wanted to hit the middle of the cooling gallery, but I went low and missed the center of it.

I then cut each section in half down the axis of the pin.

You can see the steel insert for the top ring, but I was surprised to find the two little tabs that must be joined to the steel reinforcement bands that stick out from the pin boss. I guess I'll have to cut some more to reveal what those look like exactly.

For the cooling gallery, one hole in and one hole out. I'll get a better photo of that tomorrow.

Now all I need is that LBZ piston!

Great Job Mat....

On Another Note, What Cylinders Are The Pistons Cracking? Or Is It Truely Random And Just Over Stressing The Pistons.

I sectioned an LB7 piston today and thought some of you might like to take a look. First, I baloney-sliced it down one of the ring grooves. I wanted to hit the middle of the cooling gallery, but I went low and missed the center of it.

I then cut each section in half down the axis of the pin.

You can see the steel insert for the top ring, but I was surprised to find the two little tabs that must be joined to the steel reinforcement bands that stick out from the pin boss. I guess I'll have to cut some more to reveal what those look like exactly.

For the cooling gallery, one hole in and one hole out. I'll get a better photo of that tomorrow.

Now all I need is that LBZ piston!

Great pics!!! :ro)

Any chance you could saw one piece in 1/2 perpendicular to the pin?

Just to see that the piston is cracking in the thickest direction possible, not the weakest.

I found 3 sources for glowplug chamber pressure gauges.

Siemens
Beru
Federal-Mogul

Apparently the next generation of diesel engines will have glowplugs that double as pressure sensors, and feed chamber pressure back to the ECM to adjust fuel and timing to reduce emissions and noise.

And they have normal "lab testing" pressure-only sensors that do not have a functional glowplug built in.

Does anyone have a connection with any of those three companies? I want to buy one to play with.

I read this entire thread and I am quickly becoming convinced we have a part that simply cant take the stress. These pistons are developed for peak pressures under 200 bar.

The cooled ring belt is great for long term durability and ring ductility life, but it also removes some strength from the piston for the oil to transverse through.

Mahle has many technologies available to them. I suggest a fiber reinforced, squeezed cast part that obstains from a cooled top ring cavity in the design. This does not mean the piston thermal loads cant be handled in other ways.

I run fiber reinforced squeeze cast parts in several engines that see pressures over 200 bar all the time. No cooling cavity. No troubles. Great long term durability.

Forged pistons belong in gas engines, IMO. Diesel needs a niresist ring carrier so you cant use a forged part in that case. Anodizing is a short term solution that could be used in a forged part but this is realy best for race only, low use engines.

Are all DMAX pistons gallery or cavity cooled? The Cummins did not start this until the CR engines.

Don, from my weak memory, the part number for LB7 and LLY pistons did not change. However my GM tech buddy got bored one day and found that the 06 LLYs and LBZs share the same piston part number.

So it would appear to me that we have 2 generations of pistons. Someone please correct me if I'm wrong.

Pat, I think I'm going to slice up another one...can't stop cutting :eek: ....gotta cut morrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrreeeeee eeeee :help2:

):h

By the way, is this the Don M from F1 Diesel, Mr. "Deep Enough"? If so, great to see the professor back in the house.

The LB7 and the LLY share different part numbers, although I am unsure what the difference is. I have yet to find it.

Eric, so we should be seeing 3 part numbers total?

I'll have Dan check it tomorrow.

mat, send me an email to eric@gmdieseltech.com with your email addy please.

Done. Check your spam folder if you don't get it in the next few minutes.

Mat, YGM

Mat, thanks for posting the pics.. cool stuff!

After looking at the pics from Eric it is in my opinion that the failure was simply caused from excessive cylinder pressure. The piston cracking across like it did and the bearing crush which we have confirmed are signs of excessive pressure IMO. We also found there too be bearing crush on some of the other bearings as well which makes me believe this to be the answer. Steve had mentioned a flaw in the #1 piston itself, but I think we can rule this out after seeing the bearing damage. The motor itself had approximately 30 hrs and 1200+ miles on it. The first 500 miles put on the engine were mild to moderate driving miles for break in period.

In discussion today with Eric I mentioned that I found it funny that no one had commented on the fact that the day of failure was the first day the dual CP3's were online that I had stated at the beginning of all this. This is another sign that pressure was at fault here. More fuel + more boost = More pressure.

My decision at this point until swayed is that I will be starting with a new block as the #1 cylinder wall is scored, and starting again with "New" LBZ pistons. I will be cutting the pistons again for clearance and cutting the domes to lower compression. This has been done by Garmon in the past on the Cummins with success from my understanding, and I am willing to take a step in this direction to try to solve the issue at hand.

Unfortunately due to the cost of monitoring and logging cylinder pressure I will not be doing so unless someone out there is willing to take part in an "Experiment" with me to gain some knowledge and real facts!;)

I have also spoken to Eric and have told him he may post any pictures he likes of the failures, this again is for all of us too learn from and I wish too share all. We push and keep pushing the limits of the Duramax and we can all learn from failures like this and how too keep them from happening again.

Thanks too all for their input and comments so far it is greatly appreciated!:)

Great Job Guys!! :thumb:

Looks like the next failure in line will be the bearings.

Kieth, the more I look at the way these things are cracking along the pin axis, the more I think that cutting the pistons could potentially be a major contributing factor.

I know cutting them reduces the compression ratio, which is a step in the right direction, but if you've got that much fuel and boost, it might not be near enough.

I'm going to try to draw up where I think the stresses are and see if it makes sense to anyone else.

Keith, do you have any other plans for the new pistons so that they can potentially handle more heat and pressure? Any thoughts on ceramic coating the tops?

Kieth, the more I look at the way these things are cracking along the pin axis, the more I think that cutting the pistons could potentially be a major contributing factor.

I know cutting them reduces the compression ratio, which is a step in the right direction, but if you've got that much fuel and boost, it might not be near enough.

I'm going to try to draw up where I think the stresses are and see if it makes sense to anyone else.
That brings up good points. Not much meat there to begin with, less if take some material out to lower comp.

Chad, I've been researching coatings and I think that it would be a great idea.

Keith, do you have any other plans for the new pistons so that they can potentially handle more heat and pressure? Any thoughts on ceramic coating the tops?

I think ceramic coating is an option however I have not to this point decided if I will or not. I have mixed feelings on the ceramic coating as it was brought too my attention that if not done properly flaking can occur and now you have a new problem. I am and will be taking everything into consideration and hope to come up with a "Final" plan here in the near future. We will not be rushing this by any means and will be sure to keep you all updated on our progress.

I hate to sound wet behind the ears, but given what I've seen and read I would offset bore the small end of the rod towards the crank and fit it with a new custom made wrist pin bushing. It would not weaken the rod or piston this way. Could accomplish the same compression drop as machining the top of the piston, while leaving it's integrity in tact. Not sure how much extra valve clearance is needed, but may accomplish that at the same time.

I think ceramic coating is an option however I have not to this point decided if I will or not. I have mixed feelings on the ceramic coating as it was brought too my attention that if not done properly flaking can occur and now you have a new problem. I am and will be taking everything into consideration and hope to come up with a "Final" plan here in the near future. We will not be rushing this by any means and will be sure to keep you all updated on our progress.

You should check out specialized coatings in CA, they are the ones that do all the ceramic coat work for J&E pistons and they have a long back round in coating engine internals. Just something to look into.