i seen this on the tdr site i am shocked if the difference was that great, i can see the cummins should have a bit bigger rod for the inline difference, but i looks a fair bit biggerhttp://www.turbodieselregister.com/user_gallery/sizeimage.php?&photoid=14950&width=2

I think I read somewhere that its not even a Duramax rod. Does anyone remember that?

Connecting rod size is not the total story. The Cummins needs to be a fair bit stronger/bigger to handle the extra weight of the larger/heavier piston. Being longer also increases the need for girth. All in all, proves nothing. Apples and oranges.

We have 8 rods and pistons, they have 6. The rods and pistons should be bigger on the Cummins.

The new V8 Cummins with Aluminum heads will test the Cummins loyalists' way of thinking. It would be funny if it or a MB V8 diesel replaced the 5.9 in the Dodge trucks.

When was the last time you heard of someone damaging a connecting rod? Only times I can think of are hydro lock and run-away where connecting rods have failed. Is this a bad thing? I think I would rather have a rod fail than the whole piston, crank valves and head if something goes catastrophic. And, even then who cares?

If more size, weight and volume were an advantage in a rod, wouldn't you make it a big beefy solid bar? I would rather have it as small and light as possible while being the correct strength. Like rotating mass of tires and wheels has a great effect on acceleration, mass of rods and other reciprocating parts just robs more energy.

bigger bearing surfaces? Now that might have some advantage. The piston pin looks larger diameter on the cummins and wider on the duramax. Friction is distributed over the surface area so a larger surface area might last a little longer. Again, when did a piston pin fail last?

You would really need to do a stress analysis on the whole rotating assembly in order to understand why each of the connecting rods shown in the picture is of a particular size. There are cylinder pressures(creating loads), crankshaft loads, mass, length of the rods, acceleration rates, material properties of the components and a whole bunch of other variables (which I don't know about) to take into account when designing that product. Just being bigger is not necessarily better. There are a lot of reasons why each are shaped the way they are. There are probably a dozen parameters to trade-off (each interacting in some manner with the other) to arrive at an optimal design for the product and its intended use. To truely understand, one would need to ask an expert who designs connecting rods for a living to evaluate each.

Like is mentioned above, people are raising the HP on the DMAX by over 100% and not failing the connecting rods. Looks like a lot of design margin.

Top fuelers and Top alcoholers rods are billet aluminum in most all cases. A few run Titanium. Few though. The Cummins must move 10.5% less displacement on about 25% less rods. Of couse they need to be heavier. I built about 3 times the power on my dmaxs, and they held fine.

IIRC that rod is a out of a 6.5..Super Diesel could tell us for sure......

It all comes down to the intended use and applying physics to engineer the design. I work along side stress analysts who work designs daily. Everything is modeled. What works for a Top Fuel racer may not be what a diesel engine requires to go 500K miles. And what works for a Cummins 6 cylinder diesel may not be the optimal design for a DMAX (as evidenced by the pictures).

That's a dmax rod. There just nit picking. Real story is at the dynos, track, and pullin fields. Thats where the real excuses fly. Not saying it is what they need (aluminum rods), just making more comparisons with some fact. Who is to say what is best at this point any way.

That's a dmax rod. There just nit picking. Real story is at the dynos, track, and pullin fields. Thats where the real excuses fly. Not saying it is what they need (aluminum rods), just making more comparisons with some fact. Who is to say what is best at this point any way.

As her which is better

Let's compare transmissions input shafts. ):h

I'm with Rockin', if Super Diesel can make nearly 800 hp on a stock rod, who cares? I don't get it, unless it is another ploy to win over the uninformed. Well, I'm uninformed, and I wouldn't fall for that one. . .

With a Duramax and Cummins of the same torque, the Cummins would have to sustain 25% more torque for each connecting rod. Looking at the rod bolts, and thickness around both the big and small end, I don’t see 25% or even 10% more strength.

With a Duramax and Cummins of the same torque, the Cummins would have to sustain 25% more torque for each connecting rod. Looking at the rod bolts, and thickness around both the big and small end, I don’t see 25% or even 10% more strength.

Those numbers aren't even close. Too many variables and taking 25% thrown at each rod is not correct. It would be much less in that way of looking at it.

Also, strength can't be judged simply by looking at size. It's cross sectional design, materials, manufacturing processes and actual kinematic stresses among many others.

For all we know the Dmax rod could be stronger than the other two. It's shorter for one. What's easier to break, a short stick or a long one? You just can't judge by looking at the part. A feather made of lead weighs much more than the same size natural feather.

Yeah, of all the ways to prove Dodge/Cummins superiority, that was a bogus attempt. I wouldn't argue that the Cummins is a great engine. Do they have a reputation that exceeds their true worth? Maybe. Fact is, I feel they are an excellent engine.

But I wasn't going to base my entire truck choice on engine alone. The transmission, ride, and interior were among some of the major reasons I chose a Chevy over a Dodge. I will say that the Dodge has improved significantly in recent years, and there are a few things GM needs to learn from Dodge, such as incorporating a design that will allow for decent sized tires without headaches. There, that's my $0.02!