[Cayoterun]

I guess that's the reason they used so many tranny gears, and narrow rpm spread on the engines in the early days in over the road trucks.

Back in the early 60s, I drove over the road, with GM Detroit Diesels, 220/250 Cummins, and they used 10 and 15spd trannys/w an even shift of 300rpm from top to bottom, so if you shifted right, the motors always turned 18-2,100rpm.
Mack trucks used the same principle with their tri-plex and duplex transmissions. I always like to ride with a driver that was good on-the-box, but never got the hang of split shifting them very well.

My son runs a Peter-built with a big cat and he said the torque curve is 1,400-2,200/w much more hp, so not near as much shifting. So they've improved them a lot over the years, so I guess they still use the same principle to hold a near constant engine speed as we've talked about above.

In my younger years, I sometimes wished I could have studied to be a mechanical engineer, and somehow landed a job in research and developement to understand the workings of this type of stuff.

I loved the old Detroits, but hated sleeper time, as they'd pick up a resonate vibration in the cab at a certain rpm, and would almost hurt your ears. Other wise, was a easy engine to shift behind. Also, quiet a power house for their day. I drove the old '66 CO4000 Internationals.

Thanks for your replies, and interesting, too