2021 Cummins 1075 lbft peak torque at 1356 rpm

Grit dog wrote:

4x4ord wrote:

7 th gear is 1:1 in the 10r140 and 6th is 1.277:1. So a downshift at 2114 rpm in 7th brings the engine speed to 2700 in 6th. 5th is 1.519 :1 so dropping from 6th at 2270 rpm would bring the engine up 2700 in 5th.

I hadn't looked at the ratios in a while. But looking at it, I'd drop 9th or 10th gear like a bad habit and stick with only 2 OD ratios and insert another gear somewhere between 4th and 7th, where the trans will spend most of it's time when loaded heavy.
400-500 rpm splits are great. About 100% better than my old 6 speed manual Dodge that was a challenge to get the next gear rolling before you lost 1000rpms.
But personal opinion, I'm not the guy who likes to see how low I can go on the tach and still get a load up a hill, because I've owned a couple EGT gauges and me and the EGT's are both much happier putting a few hundred more rpms through the input shaft. Thus, I don't need 3 OD ratios in a pickup truck, especially if it's not a 4.10 final ratio.
All good discussion! And pertinent to your torque rise examples. What if you could split that torq rise in half or even knock 30% off of it? Bingo, you're sitting at peak power availability more of the time. Whether you need all of it or not.
Which also helps with bsfc.

I agree with not needing 3 OD gears. Even if 10th is left at .632:1 we don't need two gears to get there. Pulling hard in OD is not really what we want for reasons like you mention as well as there is a loss in power speeding the drive shaft up just to slow thigs down again at the rear axle. Even so 63 mph is 2000 rpm with 3.55 final drive and 8th gear. The Powerstroke is putting out 400 HP at 2000 rpm so 8th gear is definitely a gear that can be used for pulling hard and it is a high enough ratio to use for light loads that 10th can't handle... we don't need 9th.

Maybe more gears between 4th and 7th would be good. The problem with more gears in between 4th and 7th is determining how to use them. With a manual transmission I can select the ratio I want depending on all sorts of parameters that I have in mind ... things like preparing for the up coming hill or slowing down for the stop sign ahead or keeping the engine brake quiet or whatever else I have in mind. An automatic can't read my mind and so it might shift up right about the time I floor the accelerator to pass someone and now it has to drop three gears. Or it might down shift right about the top of the hill and we could probably come up with all sorts of circumstances that would trigger annoying shifts especially if the ratios get too close together.