2021 Cummins 1075 lbft peak torque at 1356 rpm

RoyJ wrote:

4x4ord wrote:
^^^^ It would be nice to see the bsfc map for the 2021 Cummins. You are right that keeping the torque high and rpm low saves fuel for the heavy trucks that pull hard all day. How or where are you seeing more gears helping the Ram pickup get better fuel economy? Where on that map would you like to see a pickup truck engine run while towing a 16k - 18k trailer down the highway?

Let's build an imaginary pickup heavy hauler. 2021 Cummins dually, 10 spd Ford transmission. We'll have to assume that bsfc map applies to the new engine, with the same torque curve, just shifted up to 1458 N-m.

235/80r17 tires turn 654 rpm @ 60 mph. Let's start with 3.31 gears, here's the rpm in each gear from 45 - 75 mph:



This is where the beauty of the 10 spd shows - at every given speed we can put the engine into the rpm where peak bsfc occurs (~1500 - 2000 rpm). 6th & 7th @ 45mph, 7th or 8th @ 50, 7th & 8th @ 55, 8th & 9th @ 60, 8th & 9th & 10th @ 65, 9th & 10th @ 70, and also 9th & 10th @ 75.

The BEST part is we have 2 to 3 gears to choose and still stay within the optimal RPM. This means we can also pick the gear depending on load to get the engine torque into the optimal range.

Your 10 speed sounds like a good set up. I’ll take you on with the 6 speed Aisin if I can have 3.31 gears. I’ll bet we will find the extra gears aren’t going to buy you much. How about we pull an 18000 lb toy hauler cruising down the highway a 63 mph and say you get 9 mpg with your rig. Then we’ll go 70 mph empty and say you get 18 mpg with yours. Then we’ll climb a 7% grade towing and see how they compare. Then we can compare how they would do heading into a 20 mph wind towing at 55.