Duramax is king of the mountain again

4x4ord wrote:

Cummins12V98 wrote:

4x4ord wrote:
If the 440 hp rating of the Powerstroke is not SAE flywheel hp what else would it be?

I have no idea, they sure did not use SAE on the tow ratings except for the 450. That's why I am asking.

GM is very clear about SAE Flywheel horsepower. Seems they always did well with "less power".

I believe the reason GM was able to do so well racing up the mountains had a lot to do with the Allison gear ratios. The initial Eisenhower pull was done under the guidelines of GM. They knew exactly what torque the Duramax could deliver to the rear axle in 3rd gear. (It would be approximately 3100 lb ft of torque) They also knew that at 3000 rpm (max power rpm of the Duramax) they could do 56 mph. The F350 could put 3600 lbft of torque to the rear axle in 3rd gear but would only be capable of 48 mph @2800 rpm in 3rd gear. They needed to load the trailer such that on a 8% grade (if that's what the Eisenhower pass grade is) the load would require just under 3100 lb ft of torque on the truck's rear axles. (If the Ford shifts to 4th the rear axle torque would drop to about 2900 lbft of torque) If Ford was conducting the test they would have eanted a steeper hill or heavier trailer to prevent the Allison from coming out of second gear. The new diesels make enough torque that they won't be as easy to find holes in the gear ratios.

I did some calculations using a Engine RPM site RPM calculator. If I use a 3.73 rear ratio and 1.52 3rd gear ratio for a Ford I get 46 mph at 2773 rpm.

But if I use a 4.10 rear ratio (called the holy grail by many for towing) and 1.15 4th gear ratio I get 56 mph at 2808 rpm for the Ford.

So if Ford were to supply the correct rear ratio for their test truck I do not see the problem compared to the GM Duramax.

In fact if I use a 3.37 rear ratio and 1.41 for Allison 3rd gear
I only get 54 mph at 3020 rpm. So I would say the Ford should have the advantage. Do not forget the Ford advertises more HP than the Duramax.