Need some advice, gearing/fuel mileage.
Hey I know we have a big thread on fuel mileage going. I’m considering a 2020 Ram 3500 Crew Cab with the HO Cummins/Aisin and it has the 4.10 gears and it’s a dually. On a test drive it appeared to...
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otrfun wrote:4x4ord wrote:"3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed" vs. a 4.10. Interesting. Not what I've experienced.
According to the BSFC map for the 6.7 Cummins that Shiner posted on another thread the 3.42 pulling in 5th vs 4.10 in sixth yield very similar MPG while towing. 3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed. Again, according to the same BSFC map, towing with 3.73 gears at 65 mph should offer a slight advantage in MPG over either 3.42's or 4.10's. Empty the 3.73 will fall half way between 3.42's and 4.10's . . .
Are you making these observations based on BSFC maps of the crankshaft output of a Cummins in conjunction with gearing charts?
Or, are your observations based on BSFC maps formulated and based on on-the-road tests of production-ready, OEM Ram trucks? If so, I'd be very interested in seeing these. Could you supply a link? Thanks.
Like I said, my numbers are based off the BSFC map that Shiner had posted. I just got back from making 2 highway trips where I was able to set the cruise at 45 mph and drive uninterrupted for both trips. The first round trip was performed in 6th gear at about 1100 rpm and the truck got 28.3 mpg. The second trip was performed in 5th gear at about 1400 rpm where it got 25.3 mpg. I would challenge you to do something similar with your Ram ..... I'd be absolutely amazed if the Cummins engine doesn't give very similar results.
