tomd

Which one has the longest stroke? Does it matter?

dodgezilla04

that pic is always impressive. but most folks, not those who live in the diesel world, do not realize that the 3 engines are the same displacement(really close) but the chev's and ferds are doing it with 2 more cylinders, which makes the components smaller. 5.9L with 6 jugs vs 6.0L with 8.... the cummins are going to look much more impressive.

I remember a chevy add with the tranny input shafts compared, with the dodge being the smallest, and i saw a reply, "what good is a big input shaft, when the rods are all broken?"

NukleusX

thats a great one, couldnt help but to

gmctd

The 5.9 has the longest stroke, at 4.750 inches, give or take................

HOV

Anyone have that comparison pic of the input shafts?

P.J

Bigger is better.

dodgezilla04

it was on the back cover of a few trailer life magazines awhile back, i will look tonight and scan it if I can find it.

HOV

gracias

8910

cskal

Discounting the number of cylinders, wouldn't the longer length Cummins rod contribute to a greater torque output per cylinder? With a longer lever arm you would assume a greater torque for a given amount of input force from the piston, never mind the fact that the CTD has six larger holes (greater force) vs the eight smaller on the Chevy and Ford... Torque= Force x Lever Arm. Thoughts?

CTD NUT

I think you might be confusing rod length with stroke.....the longer stroke does mean the potential for higher torque output but it isn't the be all end all as far as torque generation is concerned as some people may have you believe. Rod ratio (the length of the rod versus the stroke of the crank) is also a key factor in torque generation. The Cummins rod has to be longer than the others just to maintain even the same rod ratio as other engines with less stroke. And it has to be beefier than the V8 rods since it has only six rods to transmit comparable forces that other engines have eight rods to transmit.

There are advantages and disadvantages to high and low rod ratios.....some of the more important factors that are considered are piston speed (the longer the rod, the lower the speed - the lower the piston speed, the worse it will perform at lower rpm), time at TDC (dwell - the higher the dwell, the more time for flame travel and complete combustion - more important at higher rpm), and piston side loading in the cylinders (shorter rods will side load the pistons in the cylinders more than longer rods since the shorter rods spend more time operating at greater angles - the higher the force the piston has to endure, the more pronounced the side load).

The engine designers must select a rod ratio that is a balance (compromise) of these factors that best suit the intended application.

tomd

Darn Good Post CTD! Thanks!

JOHNBOY6.6

CTD NUT
Very well said.

cskal

CTD:

Yes, I agree. I did just go for the simple thought here; there are other factors as you mentioned and manufacturers have to do the balancing act to achieve the best overall results. Thanks for your expansion on the thought.

dodgezilla04

i looked and looked last night and just cannot find that picture of the input shafts. i will keep trying

6speedcowboy

i've seen that board at an ag show and the Dmax and Powerstroke rods don't even come close to comparing to the Cummins. the side view is just as good.