i have talked with some people and some say that no backpressure will actually cause you to lose horsepower and is not good on the motor...just curious..?

Exhaust mods are to lower EGTs. Cat removal may throw a code because of loss of backpressure.(not sure because I don't have one)

I just installed my 5 inch straight piped exhaust and there is no loss of power.

You likely won't lose power and there will ALWAYS be some backpressure as long as there is an exhaust system on because the pipe it self will provide at least a little resistance to flow. It just won't be as much resistance as before. ;)


C-ya

There will never be no backpressure due to the turbo. Guys at the truck pulls run a one to two foot pipe right off the turbo and they dont hurt for power!

You don't need backpresure. You need velocity. People get it confused because if you go to big to quick you lose your velocity and heat. If you do this the gases slow down to were they have to be pushed. Same is true if your tubing is to small.So you run a huge pipe right off the head or turbo the exhaust slows way down, Then a guy says you need back presure. Thats false. You need to find the right size of tube to keep the gases moving fast. Go too small and you have back presure, thats bad. I don't know why you'd ever want used exhaust to sit at the tubo outlet with no were to go. Same goes for an exhaust valve. We've proven this time and time again. From the late 50s to present with our steped down pipes on the fords. Once it's down stream aways all the witch craft is gone. So the debate between 4" & 5" is a mute point. Really no advantage or dis advantage. Thanks, Jerod Jardine

Concerning our Duramax's or any diesel's for that matter, you do not need backpressure or velocity in the exhaust being the turbo is doing all that work for you. This concept does apply to gas motors but not to our trucks.

Bentley

Concerning our Duramax's or any diesel's for that matter, you do not need backpressure or velocity in the exhaust being the turbo is doing all that work for you. This concept does apply to gas motors but not to our trucks.

BentleyYou do need to keep your velocity up on a diesel. I put a full system on my 03 and it killed my bottom end. I lost about 3 mph it the 1/4, I put my stock 3.5" front pipe back on that had no cat and left the 4" muffler and tailpipe on and got my bottom end and 1/4 mile speed back up. It was enough power loss to feel with no problem. I know all trucks are not alike but I would suggest to anyone with a 4" or larger front pipe to just take a couple hours and do a test and try a stock front pipe with their after market muffler and tail pipe, I guarantee you will be suprised. I'm not basing this on Physics, I'm basing this on my findings on my 03 LB7.

Yes yellow jacket is right and wrong, in a perfect word we could run a 2' stack out the hood. When most trucks have to run about 17' foot of tubing velocity and down pipe desing comes into play. You'll always have some back presure due to wall drag. We did alot of dyno work on the fords and runing a steped down pipe, about 18" of 3.5 " then 4 from their back we would pick up about 13# of tourqe right of idle. We wouldn't lose any on top compared to a full 4in sys though. I'm working on the same set up right nowfor the duramax.

You do need to keep your velocity up on a diesel. I put a full system on my 03 and it killed my bottom end. I lost about 3 mph it the 1/4, I put my stock 3.5" front pipe back on that had no cat and left the 4" muffler and tailpipe on and got my bottom end and 1/4 mile speed back up. It was enough power loss to feel with no problem. I know all trucks are not alike but I would suggest to anyone with a 4" or larger front pipe to just take a couple hours and do a test and try a stock front pipe with their after market muffler and tail pipe, I guarantee you will be suprised. I'm not basing this on Physics, I'm basing this on my findings on my 03 LB7.

This makes zero sense to me. Can someone explain?

Jerod, am i hearing you right?
are you saying i should leave the stock turbo outlet on, and step up to 4" pipe 1-2 feet after the turbo outlet?
I have a full 4" turbo back system in the garage right now! It would be good to know before i install it on my LBZ!

Thanks !

There is a down pipe from the turbo down to the chassis. Then there is a front pipe that has the Cat. Then there is the exhaust. I find it hard to believe that going 4" from the downpipe back would decrease performance.

If you step the front pipe up to 4", you may have a little turbo lag right off idle. The real purpose of increasing the front pipe size is to lower egts, which is what just about everyone is looking for. If you race or sledpull, you are gonna do a boosted launch, so it does not matter if you lose spool up speed because you are building boost before launching. Like everything, it has its pros and cons, but pros for the most part.

I could see that velocity would be lower if the tube into the turbo were bigger but how can that be with the tube after the turbo?

So we should be putting a 4" system on from the downpipe back? I am wondering because I am about to get a 4" system and do not want to sacrifice turbo spool up time, and do not want to buy extra parts that I won't use.

I think most folks who put a catless 4" backpipe are happy. I would say get the catless pipe if you are worried about EGTs / running big HP. Get a cat back system (leaving the cat and frontpipe alone) if you don't run huge HP or tow heavy. Also if you want to stay more quiet keep the cat. If you want to get louder go with the catless frontpipe.

Remember that the catless pipe may throw codes and you'll have to deal with that with a code blocker or programming.

The cats gotta go. EGT's are a bigger concern than noise.

That's what I would do. I didn't have a cat on my 01. My buddy has a cat back system on his 05 but he is not towing or running big hp so he has no worries. He wanted quiet. I think catback systems are a bit easier to instal and a bit less $$ too.

So we should be putting a 4" system on from the downpipe back? I am wondering because I am about to get a 4" system and do not want to sacrifice turbo spool up time, and do not want to buy extra parts that I won't use.

you personally, wouldn't have that much of a problem w/ spool up considering you have a boost stick. i'm running a ppe boost controller and if i set it up right i get almost no turbo lag. and i'm running no cat no muffler to 5" stacks. i used to have it out the pass side w/ the stock muffler and no cat before the tire and i noticed quite a difference switching to the no muffler stack set up. mostly in throttle response. but i'll tell you this, if your looking for quite thats not the set up for you.

That's what I would do. I didn't have a cat on my 01. My buddy has a cat back system on his 05 but he is not towing or running big hp so he has no worries. He wanted quiet. I think catback systems are a bit easier to instal and a bit less $$ too.What you are planning in my openion is the best setup for a LB7 that is'nt heavily modded. You'll save money, install in less time, and wont risk loosing your bottom and midrange. You might not get as much drop in egts but I dont thing the difference will hardly be noticeable.

Backpressure is BS! the split second its forced through the turbo its done...not needed. It doesnt matter where or what happens to it then.

SleeperTRK, did you notice more turbo lag after you installed your exhaust with the cat delete? I certainly don't want any more turbo lag than there already is, but I would sure like to get rid of the cat.

Lets think about this: where is the smallest passage in the exhause system? the turbo, right? so when your pushing all that gas through that tiny hole, therein lies all your back pressure to the engine. anything that takes place behind the turbine wheel should be to reduce flow resistance, hence reduce EGT. the efect being created by steping up the size of pipe is to efectively create a small amount of vacuum, simmiler to the way a megaphone increases volume. this in turn aids in evacuation of exhause gas, but for it to be efective the lengths must be the correct size and in the correct position for the overall length of the exhaust, as you are using the inertia of the gas to create the vacuum. as far as loosing botom end, what you would lose would be the non-boosted portion of your powerband, where the "naturally apirated" efects come into play. Just my bit-o-advice from my own expirience.

Good Luck,
Mike

So are you saying that there will be no effect on turbo spool-up? Is this a function of the inertia of the turbo itself and nothing else?

There are some other factors involved, but as fas as noticeable loss of turbo spool, especailly with a VVT turbo, I don't see it happening. I have a 4" from the downpipe flange back, and I only noticed good things. no losses, only gains. and my turbo vanes aren't variable...

Sounds good to me. I do want the cat to go, so that is what I will do.

I can tell you this after installing my 5" system. The front up pipe is 4 inches. Then it steps to five right after that(at the crossmember). I tow almost everyday and havent noticed any bottom end loss. Towing at highway speeds it seems like I've gained a pound or so of boost. Unloaded the power seems smoother not as much as a shock when the boost comes on but truck isn't slower from what I feel is a better power band. Which might make some people feel they lost bottom end since the power is smoother rather than a quick spike in power which makes you think there is more power. There may be a small increase in turbo lag off idle or low rpm(850-1000) than with the stock exhaust with straight through muffler when your putting through town but after that low of rpm then all is good. I've got better egts and in my opinion a better power cruve with my 5". Not to mention the 6" stainless steel tip looks great.

SleeperTRK, did you notice more turbo lag after you installed your exhaust with the cat delete? I certainly don't want any more turbo lag than there already is, but I would sure like to get rid of the cat.

Nope, i just noticed a little more power :D

There's a definite improvment going to a four inch exhaust. It's been proven time and again. The turbo is the biggest restriction in the exhaust stream. If you can build a velocity higher than what the turbo produces you'll create a vacume. If you can achive this you'll help the turbo become more eficient. You do this by finding the right diam. and length of tubing. If the turbo is more eficient you'll have less egt and quicker spool. Thanks, Jerod Jardine

Currently im running a 4" downpipe to a 5" stack set up. Its making power that i didnt feel with my stock set up. Before that i ran a 4" downpipe that was a 5" after cat set up. I felt a huge loss in power with this and turbo lag in mid to high range. No muffler or cat on either set up strickly streight pipe, and i have yet to trip any codes. I have an '03 read my sig for mods. .

I ran my truck once without the muffler and it didnt feel as strong to me which is why i left my mufler on.

You do need to keep your velocity up on a diesel. I put a full system on my 03 and it killed my bottom end. I lost about 3 mph it the 1/4

something else was causing the drop in 1/4 mile time. It wasnt the exhaust.;)

There's a definite improvment going to a four inch exhaust. It's been proven time and again. The turbo is the biggest restriction in the exhaust stream. If you can build a velocity higher than what the turbo produces you'll create a vacume. If you can achive this you'll help the turbo become more eficient. You do this by finding the right diam. and length of tubing. If the turbo is more eficient you'll have less egt and quicker spool. Thanks, Jerod Jardine


Listen to this guy.... he knows what hes talking about. Alot of people say you need "some backpressure" this is false, doesnt matter if its gas or diesel. No motor needs backpressure what it needs the correct exaust "pulse or velocity" with that the exaust gasses will actually start to pull themselves out of the pipe:D

Can somebody please answer the original question somewhat definitively? I would really like to Straight pipe my truck but if im going to lost more than 15 hp then i probably wont do it.

Stupid question but has anyone dynoed with a muffler then again without one on a 4 or 5" exhaust?

I remember hearing somewhere that unless your running 500rwhp (not sure of exact #) and you use a 5" you will actually loose power.

Bla, Bla, Bla

Sorry guess we kinda got off track...... 4 or 5 isnt going to make alot of difference cause the down pipe will still be 4'' (correct me if im wrong) 4" is sufficent for most people. With or without a muffler.... you will not notice much if any horsepower difference, just depends how loud you want it :D Hope this helps

P.S. Some mufflers seem to cause alot of interior drone, straight pipes also draw more attention):h

....No motor needs backpressure what it needs the correct exaust "pulse or velocity" with that the exaust gasses will actually start to pull themselves out of the pipe:D

Thes guy NAILD it! using the correct sizes of pipe, transitions placed stratigically, and proper lengths, the exhaust will effecively "pull itslef" out of the engine, so to speak.

As far as loosing any power from the engine by changing exhaust, its tough to "feel" anything above or below a 20 or 30 HP gain or loss. and power production will varry by as much as 15 HP, sometimes more, day to day, depending on fuel quality, ambiant temperature, barometric pressure, so on and so forth. Like it was said before in this thred, use the exhaust that gets you the tone you want, you most likely won't notice any gain or loss in power, except on a dyno...what you WILL notice is a change in EGT, and with a larger pipe, causing a reduction in EGT, you can run a higher HP tune. and that is the reason for the larger exhaust systems on a diesel, especially a turbo diesel.

and for the 4 or 5 debate...what happens behind the flattened down pipe (the REAL down pipe, the one connected directly to the turbo) won't have as big an efect if its not enlarged first. you could put a 10 inch exhaust on these things, and it won't make a bit of difference over a 4 inch till you change that down pipe. (aside from a change in tone... :D )

Ive always wanted to straight pipe my truck ( Ihave a banks 4") but I dont want to loose power. If Im not going to loose any power then ***** it, the mufflers comin off

something else was causing the drop in 1/4 mile time. It wasnt the exhaust.;)I had a friend clock me in an x-patrol car, stock my truck did 81 mph. I drove into the shop installed the full 4 inch system 45 min later he clocked me again, I did 78 mph, I drove back into the shop put the stock front pipe on that had no cat. We clocked the truck again, 81 mph. I'm all ears what was my problem?

I had a friend clock me in an x-patrol car, stock my truck did 81 mph. I drove into the shop installed the full 4 inch system 45 min later he clocked me again, I did 78 mph, I drove back into the shop put the stock front pipe on that had no cat. We clocked the truck again, 81 mph. I'm all ears what was my problem?

So during these tests it was the exact same outside air temp, exact same fuel temp, trans temp, engine temp, You launched at exacly the same rpm, the same boost levels, and in the exact same place on the road, distance traveled down the road was the same, your friend shot the radar at the exact same point on the road?? There are alot of different variables....like Ben said, It wasnt your exhaust. :rolleyes:

So during these tests it was the exact same outside air temp, exact same fuel temp, trans temp, engine temp, You launched at exacly the same rpm, the same boost levels, and in the exact same place on the road, distance traveled down the road was the same, your friend shot the radar at the exact same point on the road?? There are alot of different variables....like Ben said, It wasnt your exhaust. :rolleyes:Same temp same distance same radar same truck same driver same launch different exaust setup. Seat of the pants was a big difference. I'm not trying to be a now it all smart a-- I'm just stating the facts, like I said before I'm all ears If it was'nt my exhaust please let me know what it could have been. Keep in mind this truck was totally stock this was my first mod, no tunner, no big head or intake. The difference in power was easily noticed before I got the results from the radar.

JhnZ71, the differance between a st. piped kit and a muffled kit is minamal. It favors the muffler though. If you want the tone, pull the muffler of. As far as 5" goes it dosen't really help any thing until you start producing some h.p. As far as the stock down pipe, the one off the turbo, it flows surprisenly well. We've built some out of 3.5" and 4" and didn't see that much of an improvment over stock. Not enough to produce it and sell it to a guy any way. I hope you got your question answered. Thanks, Jerod Jardine

There is a different is exhaust selection between naturaly aspirated and forced induction set ups. Naturaly aspirated you can go to big and lose velocity which the velocity helps create a vaccum effect to help the intake stroke due to cam overlap. Until you put a bigger down pipe and I don't mean the furthest up pipe on our exhaust then you will change the velocity right after the turbo. Everything down stream from the actual down pipe is a restriction which when you restrict the exhaust exiting a turbo engine you creat backpressure which will cause the turbo to spool slower since the velocity of the exhaust at a given rpm can't flow across the turbine as fast as it would if it was more free flowing down stream. When the exhaust can't escape fast enough your egts will be more. Look at the comparison between cat back and full exhaust. Full yeilds a little more power, probably not noticable to the butt dyno, but keeps the egts down better. All do to more free flowing. Like I said about my exhaust, I pull a trailer everyday and with my exhaust over my stock exhaust with a straight threw muffler my truck builds boost quicker and runs cooler egts. The stocker out of the hole would have more lag then when the engine came to a certain rpm it would come on fast along with egts. On the highway loaded and unloaded I run one maybe two more pounds of boost than before. Power band is much smoother.

I was talking about 4" vs 5". I probably didn't make myself clear. Their is a diferance between nat. aspirated and turboed engines and some of the principals are out the window. But velocity is still somewhat important.

jerod, why don't you see if you could organise some sort of test with different exhaust setups, cat back vs full 4" vs full 5" vs stock. Mix match some 4" and 5" stuff. This seems like something everyone is very interested in and everyone seem to have different openions but no one has actually done any test. I did one myself but when I posted my results I was told that what happened did'nt really happen. I think the most affected would be the LB7 I also think the results would be very surprising. I would be more interested in performance results than dyno results.

This is a good idea, except that the dyno would not lie. As for performance results, you will always have people who don't believe what you are saying. With dyno numbers, it is pretty cut and dried.

This is a good idea, except that the dyno would not lie. As for performance results, you will always have people who don't believe what you are saying. With dyno numbers, it is pretty cut and dried.Your right, the dyno wont lie its right there for all to see. I mentioned performance test because sometimes just because one mod gives you more peak hp than another, it does'nt allways mean it will perform better. But a dyno is definately an easy way to see imediate results. I have a cat back system on my 06, I have been tossing the idea around of removing my cat. I think Ill rig up a stock size cat delete pipe and order a 4" front pipe. Theres a dyno about 40 miles from my home I could try the stock size front pipe and the 4" front pipe within an hour and also dyno the truck with the cat in place. I may end up with a slightly used 4" front pipe for sale, It will definately be interesting to see.

Yeah, wish I had access to a dyno like that. It will be interesting to see your results.

Velocity is important but the thing that stops making any more velocity on these trucks is going to be the actual down pipe on the turbo. If there are gains by having a muffler then why are most of the faster guys with tuning running straight piped exhaust? Egts are takin into consideration with this question but a few seconds down the strip at a slightly higher egt which would be marginal, why wouldn't a guy want the extra power if there is some with a muffler since it could mean a 13.00 pass to a 12.99 pass or even quicker? To me a dyno comparison would have to be done by a person that isn't selling exhaust and by someone who runs a dyno everyday. You wouldn't want me to test in house something of mine that I'm selling against someone elses products or ideas since the outcome could be bias. A muffler is a sound/loudness prefference and brings the over all cost of these exhaust system higher in my opinion. Have someone that owns a dyno that isnt selling or trying to sell a product do the testing for credability. Now before I get flamed I am in no way shape or form accusing anyone of anything just want a fair playing field with honest answers and findings of these tests thats all. Also I'm not trying to stop anyone from making money by buying or selling mufflers. Jerod Jardine I am in no way attacking or accusing you of anything and enjoy this discusion with you not trying to be a pain or argue but taking in everything you said since I've bought your exhaust systems for my other toys in the past.

Hope I did'nt strike a nerve. I mainly want to go to the dyno for my own satisfaction. I am very interested especially after my experience with my exhaust on my 03. If I do decide to do this I will still post my findings for those who are curious.

we've been building exhaust systems for a long time. 90% of our advertising is word of mouth. I've seen alot of fudged dyno numbers. Our company belives in selling buy not selling. If you buy our kit and it dosn't do or feel what we say it will your not going to tell your buddy about it. If brand x is better I'm not going to say our is better, I think honesty is way more important. Right now the dyno is pretty backed up. I've always wanted to do a no bs dyno thing. We've done dyno work on all the above but never same truck and the same time and the results were similar to as stated above. It would be intresting though. I also like talking to you guys and don't take any offense to much of anything. Yes, selling stuff is my main purpose here but I also enjoy talking and reading about all the other things. Thanks, Jerod.

and for the 4 or 5 debate...what happens behind the flattened down pipe (the REAL down pipe, the one connected directly to the turbo) won't have as big an efect if its not enlarged first. you could put a 10 inch exhaust on these things, and it won't make a bit of difference over a 4 inch till you change that down pipe. (aside from a change in tone... :D )

exactly!!!!

how many of you have seen a stock duramax downpipe?? You guys think you're 100% freeing up the engine by putting a 5" exhaust on??!:eek: :D

Same temp same distance same radar same truck same driver same launch different exaust setup. Seat of the pants was a big difference. I'm not trying to be a now it all smart a-- I'm just stating the facts, like I said before I'm all ears If it was'nt my exhaust please let me know what it could have been. Keep in mind this truck was totally stock this was my first mod, no tunner, no big head or intake. The difference in power was easily noticed before I got the results from the radar.

you dont have to beleive me, but myself and many other people are telling you its NOT the exhaust. Do you know how much backpressure/drive pressure a stock LBZ turbo creates?:)

as long as your exhaust system doesnt restrict enough flow to create 60+ psi of back pressure, its not having ANY effect on exhaust flow rate/velocity/whatever (because the turbo is generating all the back pressure)

second of all, it doesnt matter regardless. Its a diesel. There is no (need) for a cat. There are no 02 sensors. You cant run a diesel "rich" or "lean". There is no throttle plate. There is a turbo, a variable vane one at that (10x worse as far as creating drive pressure). ;)

ben

i have a few questions as i am still earning way to much about these trucks. One: can i put a better down pipe on with the stock cat, to stay in the warentee? Two: what does the 2006 LBZ have as far as stock boost? Three: what can you do, other than a chip, to get more power or boost?
thanks, jimmy

you dont have to beleive me, but myself and many other people are telling you its NOT the exhaust. Do you know how much backpressure/drive pressure a stock LBZ turbo creates?:)

as long as your exhaust system doesnt restrict enough flow to create 60+ psi of back pressure, its not having ANY effect on exhaust flow rate/velocity/whatever (because the turbo is generating all the back pressure)

second of all, it doesnt matter regardless. Its a diesel. There is no (need) for a cat. There are no 02 sensors. You cant run a diesel "rich" or "lean". There is no throttle plate. There is a turbo, a variable vane one at that (10x worse as far as creating drive pressure). ;)

benBen I can tell buy your posts you know allot about the Duramax. I hope you don't think I'm doubting your experience, It probably does'nt make any difference, but the truck I had my exhaust issue with was an LB7. I know it does'nt sound logical that a larger front pipe would have that kind of impact on a turbo diesels performance, I just can't think of any other possible explination.