Took the plunge - Cummins to Hemi 6.4
After reading posts, reviews, specs, watching videos, and a few test drives, I finally decided to take the plunge. I sold my 2003 Ram 2500 QC LB 4x4 Standard output 5.9 Cummins 5 speed and bought a ne...
Forum Discussion
blderman wrote:
Here is a brief example based on trans/rear end gear ratios. I know this isn't proof of anything but it shows the design flaw, in my opinion.
Ram 6.4 (420ft lbs @ 4000 rpm)
1st Gear 3.23= 1,356 ft.lbs x 4.10 rear= 5,559 ft.lbs
2nd Gear 1.84= 772 ft.lbs x 4.10 rear= 3,165 ft.lbs
Chevy 6.0 (380ft.lbs @ 4200rpm)
1st Gear 4.03= 1,531 ft.lbs x 4.10 rear= 6,277 ft.lbs
2nd Gear 2.36= 896 ft.lbs x 4.10 rear= 3,673 ft.lbs
So mathematically speaking the Chevy has 718 ft.lbs more in 1st gear and 508 ft.lbs more in 2nd gear. If my math is correct that is a substantial difference in torque to the rear wheels. If the Ram had the same gear ratios as the Chevy it would have walked away easily.
Your numbers are slightly off - not that it would make much difference. The 6.4L Hemi is rated at 429 tq, not 420.
When you look at the tests results I posted above, if the paper figures translate to real world performance, the GM should have been faster when compared to the RAM in any test that had the trucks compared when in 1st or 2nd gear. My 4.10 equipped truck shifts out of 1st at 40 mph, and will go to about 72 mph in 2nd. So, any test that went to 40 mph or 60 mph, the Gm should have been faster, but it wasn't.
I think it has to do with the engine calibration when at high altitudes. The Davis Dam grade and the 7.2 grade they used at the Milford proving grounds don't show a performance deficit for the RAM, and they involved towing and empty runs going uphill. The only common denominator is the high elevation.
