Does any have a legitimate photo of the Duramax connecting rod vs. a Cummins Con-Rod. My neighbor, Mr Cummins :-( brings over a picture of the Cummins rod vs. Duramax rod showing how much bigger it was supposed to be. It was the worse job of Photoship I had ever seen!!

I have seen both rods in person, but never laid out side by side. From what I can recall, the Duramax rod was much stouter, uses bolts that are bigger ( 9/16 vs. 7/16 - I am estimating) and has bigger journals on both ends. Obvouisly, the Cummins was longer, but extra length means less strength to me, not more.

If anyone could post a REAL photo of these con-rods, it would be appreicated. Thanks much.

D

PS - Thanks for the info on ordering the Hi-Po version of the Duramax. I plan on ordering mine about the end of September. Can't wait.

I remember seeing the picture of the big 3

IIRC, it was a Cummins, a PowerStroke, and supposedly a Duramax, though I remember someone saying it may have been a 6.5 rod, not the Duramax. Don't know for sure.

One thing to remember, you dont hear of either engine spitting rods out the sides of the block, so they're each obviously strong enough for their application.

Was the Duramax the stoutest looking rod, at least from thickness and bearing journal size?

As far as throwing rods out the side, you are correct I have not heard of any problems with anyones engnes. However, I saw some pix another truck site showing where Cummins blocks are cracking big time. Not sure of the years, but I assume these are newer engines, since it just came out.

THanks Again

I'm sure the cummins rod will still dwarf the DMAX rod. One rod per journal and more room in the cummins. Bigger doesn't necessarily mean better. I'd rather take an F18 into a dog fight than a 747.

Here ya go.

I just used the search feature. Took 30 seconds.

http://dieselplace.com/forum/showthread.php?t=18349&highlight=connecting+rod

One thing to remember, you dont hear of either engine spitting rods out the sides of the block, so they're each obviously strong enough for their application.

Seems like late in June 2 rods got kicked out of dmax blocks, was a topic of conversation at TiM.

TiM <-----?

http://www.gmdieseltech.com/images1/lly_bentrod.gif[img]

Thanks for the feedback. I also have my doubts on the accuracy of the pix as well. As you all have mentioned, there is more the store than meets the eye.

Material is the first that comes to mind. I have read that GM is utilizing an aircraft grade of 4340 alloy steel, forged then heat treated to Rc 45 - 50 for ultimate tensile strength of nearly 300,000 PSI.

On the other hand, I have read that Dodge is using a ductile iron casting for their connecting rods to save money. Probably 65-45-12 ductile iron. The "65" in this material spec is the ultimate tensile strengh. This means that it is 65,000 PSI.

Some quick math yields a factor of nearly 5 to 1. When you use weaker material, you need a lot more of it. It is as simple as that.....

Thx

THe pic I posted tells me it aint enough yet. Thats from an LLY

THe pic I posted tells me it aint enough yet. Thats from an LLY
:eek: Stacked Boxs' or nawws or both. That was not good, warranty ??? LOL

Thanks for the feedback. I also have my doubts on the accuracy of the pix as well. As you all have mentioned, there is more the store than meets the eye.

Material is the first that comes to mind. I have read that GM is utilizing an aircraft grade of 4340 alloy steel, forged then heat treated to Rc 45 - 50 for ultimate tensile strength of nearly 300,000 PSI.

On the other hand, I have read that Dodge is using a ductile iron casting for their connecting rods to save money. Probably 65-45-12 ductile iron. The "65" in this material spec is the ultimate tensile strengh. This means that it is 65,000 PSI.

Some quick math yields a factor of nearly 5 to 1. When you use weaker material, you need a lot more of it. It is as simple as that.....

Thx

You need to go a lot deeper than that. First, ultimate tensile strength means a lot for bolts in tension, but not for rods. Yield strength is much more important, and so is its ductility post-yield.

The other side of the equation is the section design. Higher stresses are usually more easily handled by redesigning the section of the part rather than going to an expensive material. The design's section modulus is the key.

Most of these "comparisons" are just marketing bull$hit.

THe pic I posted tells me it aint enough yet. Thats from an LLYWell, how about telling us the story behind that rod? Rods don't just bend with out a good abuse or neglect story behind it.

heres the top view

http://www.gmdieseltech.com/images1/lly_turbo.jpg

I know that truck! Saw that big scrolly thing up close. It makes a lot of smoke and spits out a lot of rubber on the road...

IIRC, the longer the "throw" and/or longer the rod, the more torque the engine makes. Also, the higher the reciprocating weight (piston), the larger the rod needs to be.

What I don't understand is the Cummins and P-Stroke end cap design. Wouldn't that angled cap put more stress on the bolts and cap, considering the force is being applied downward? You don't have the "area" on the crank journal that a "flat" endcap would have...

Duramax rods also use fracture cap technology, not rebuildable, but strong! Longer rods are not weaker when used with less angle, like in the Cummins, Ford's using powdered rods now, bad news for sport tunning!
Maxi's rod photo looks like the victim of a hydro lock?

What I don't understand is the Cummins and P-Stroke end cap design. Wouldn't that angled cap put more stress on the bolts and cap, considering the force is being applied downward? You don't have the "area" on the crank journal that a "flat" endcap would have...

Actually, "offset" rods like that have been used for years, Tom....They offer better clearance in the bottom end (to miss camshafts, block webbing, etc) I know Deere has used them for a long time in certain engines, as well as many others...
Since there is rotational force involved, I don't feel they are at any disadvantage..

Almost looks like a little too much propane......

TiM <-----?
THUNDER at IRP, I was typing and not thinking :mad:

Of course the Cummins rods are going to be bigger. They have more load per rod, since there are only 6 of them. I'll use this analogy...A Cummins makes 100 lb.ft/ cylinder while a Duramax is 75. Tell your neighbor to take a hike.

I have probably rebuilt or replace and installed nearly 1500 + engines in my life very few have rod failure. Most bottom end failures come from a bearing failing. Most were caused by a blown head gasket that had washed out the bearings with antifreeze and the engine had been run with a mix of water and oil. Then they fixed the head gasket and changed the oil. But it was to late the damage was done it is just a matter of time before the bearings fail. Upper engine failures seem to develop mostly from a dropped valve or a busted piston thus allowing the rod to exit the side of the engine. I would not worry about the size or shape of the CUMMINGS, FORD, CAT, or GM rods they all perform very well.

That LLY had it's share of injector trouble (6 of 8 replaced). We believe an injector hung open and dumped a bunch fuel into that one cylinder hydrolocking it and bending the rod. The other 7 were fine.

You also need to remember crank shaft stroke, rod ratio, and rotating mass, as well as all the other things mentioned, play into the size and girth of a rod.

I know that truck! Saw that big scrolly thing up close. It makes a lot of smoke and spits out a lot of rubber on the road...

IIRC, the longer the "throw" and/or longer the rod, the more torque the engine makes. Also, the higher the reciprocating weight (piston), the larger the rod needs to be.

What I don't understand is the Cummins and P-Stroke end cap design. Wouldn't that angled cap put more stress on the bolts and cap, considering the force is being applied downward? You don't have the "area" on the crank journal that a "flat" endcap would have...

Not true, short rods make more low torque, long rods for the same stroke make more upper rpm torque. Much to do with the time the piston dwells at TDC, and the position the the piston is when the rod is 90 degrees to the crank throw (max leverage).

Absolutely correct. For example: I used to build ricers, and with N/A motors, we have actually added metal to the top of the block to allow longer rods for this reason. Look at some of the crotch rocket rods if you need more proof.

has anyone compared oil temperature between the Dmax and the Cummins? That large journal diameter on the cummins is creating at lot more heat than the smaller journal in the Dmax.

That LLY had it's share of injector trouble (6 of 8 replaced). We believe an injector hung open and dumped a bunch fuel into that one cylinder hydrolocking it and bending the rod. The other 7 were fine.

Yeah, and GM says that it won't hurt anything.:rolleyes:

Not true, short rods make more low torque, long rods for the same stroke make more upper rpm torque. Much to do with the time the piston dwells at TDC, and the position the the piston is when the rod is 90 degrees to the crank throw (max leverage).

How can a short rod and a long rod have the same stroke? :help:

Not true, short rods make more low torque, long rods for the same stroke make more upper rpm torque. Much to do with the time the piston dwells at TDC, and the position the the piston is when the rod is 90 degrees to the crank throw (max leverage).

Thanks.

How can a short rod and a long rod have the same stroke? :help:

Different deck heights (distance from the main bearing centerline to the headgasket.

Long and short rods are hotly contested. Short rods lose more power from piston skirt loading, but long rods add reciprocating mass to the bottom end and weight to the block. A lot of tuners like running long rods in tall blocks with stroker motors to reduce the skirt loading.

The peak leverage torque on a crank is related to the rod length. A short rod puts the peak leverage earlier in crankshaft position than a long rod does. No engine puts peak torque at 90° ATDC. The shorter the rod, sooner peak leverage occurs at. Rod length affects optimum ignition timing.

All things being equal, a long rod is better. But when you look at weight and strength, you realize that there is a balancing point.

Different deck heights (distance from the main bearing centerline to the headgasket.

Long and short rods are hotly contested. Short rods lose more power from piston skirt loading, but long rods add reciprocating mass to the bottom end and weight to the block. A lot of tuners like running long rods in tall blocks with stroker motors to reduce the skirt loading.

The peak leverage torque on a crank is related to the rod length. A short rod puts the peak leverage earlier in crankshaft position than a long rod does. No engine puts peak torque at 90° ATDC. The shorter the rod, sooner peak leverage occurs at. Rod length affects optimum ignition timing.

All things being equal, a long rod is better. But when you look at weight and strength, you realize that there is a balancing point.



Spare the rod, Spoil the engine :lol:

How can a short rod and a long rod have the same stroke? :help:

It's amazing how many people ask this question...and even argue about it..

The length of a connecting rod has nothing to do with the stroke (throw) of a crankshaft....Regardless if you have a 2" con. rod or an 8" con. rod, the piston will only move as far the crankshaft stroke is...
Or, another way to look at it is to look at the cubic inches forumula...

((Bore x Bore) / 4) * # of cylinders * pi (3.1415) * stroke

It's amazing how many people ask this question...and even argue about it..

The length of a connecting rod has nothing to do with the stroke (throw) of a crankshaft....Regardless if you have a 2" con. rod or an 8" con. rod, the piston will only move as far the crankshaft stroke is...
Or, another way to look at it is to look at the cubic inches forumula...

((Bore x Bore) / 4) * # of cylinders * pi (3.1415) * stroke

That is correct. No matter how long your rod is, it makes no difference. It's the stroke that matters.

6.5TD, 7.3 PSD, Cummins


http://www.fordcummins.com/images/rodcomparison.jpg



http://www.turbodieselregister.com/user_gallery/sizeimage.php?&photoid=5594&width=1

Hoot that picture is not a navistar 6.0 rod I just went on a plant tour in Indy with the powerfest rally. The 6.0 rod is much more beefy with an offset cap. the problem with the navistar six point oooh is the heads they only have 10 bolts per head. The 7.3 has 18 and the duramax has 22 bolts per head.

Different deck heights (distance from the main bearing centerline to the headgasket.

Long and short rods are hotly contested. Short rods lose more power from piston skirt loading, but long rods add reciprocating mass to the bottom end and weight to the block. A lot of tuners like running long rods in tall blocks with stroker motors to reduce the skirt loading.

The peak leverage torque on a crank is related to the rod length. A short rod puts the peak leverage earlier in crankshaft position than a long rod does. No engine puts peak torque at 90° ATDC. The shorter the rod, sooner peak leverage occurs at. Rod length affects optimum ignition timing.

All things being equal, a long rod is better. But when you look at weight and strength, you realize that there is a balancing point.

Thanks! :exactly:

Hoot that picture is not a navistar 6.0 rod I just went on a plant tour in Indy with the powerfest rally. The 6.0 rod is much more beefy with an offset cap. the problem with the navistar six point oooh is the heads they only have 10 bolts per head. The 7.3 has 18 and the duramax has 22 bolts per head.

I did a quick search for pics and that's what I came up with. Did another.. I believe this one is paydirt.

More an more you hear the 6.0 really is a poor excuse for a diesel. Not only do they have fewer head bolts, the bolts are extra long, having to sandwich a two piece (aluminum on top of cast iron) head onto the block.

so far from what i have seen with the duramax, the rods seam to be the week spot, i have went threw my own bent rods as well as others i know, i use water injection witch i think was the culprit,(due to the squash factor) but a buddy did not, and also had a bent rod, the three i have seen have all been associated with been making over the 600hp, my dealers tech have seen a few but blamed on injector hydrolock, as eric and micheal have seen, banks sent me a bit of litachure on their findings and hope to try their idea out of hardened rods in the future
also know of others on this site that have had rod problems with high hp, seams to be the durmax weak point, hope they made them stronger on the new motors

That is correct. No matter how long your rod is, it makes no difference. It's the stroke that matters.

That line looks like it belongs in an off topic thread :lol: