PTO HP

A few years back I would have scoffed at the idea of cruise control in a highway tractor. They do work and work well. I have tried this with all of them and leave it on cruise, is the answer. There is a limit of course and you must shift.

Most of us grew up on cars and pickups with gas engines where it was pedal to the metal for power, just not so with diesel. In actual fact most diesels develop their max torque at or below 1500 rpm.

One job I have done is haul logs on ice roads with hills. You do as little shifting as possible, as it causes truck to spin out on the ice. Here is where the Cat and the Mack shine. I have seen those engines lug to 800 rpm and yes recover. Not recomended by the experts, but one H#$% of a lot better than going down the hill backwards.

Rod

Therefore, hp is dependent upon torque and rpm. All Otto cycle engines develop maximum torque at something much less than their maximum rpm. For most tractor engines it's 60% to 80% of maximum rpm but there are a lot of variables. Whoever told you that you lose hp at high rpm is correct. Best bet is to run to an rpm that's slightly above the rpm at which peak torque is developed and then shift. This lets the engine accelerate as fast as possible.

Tractor manufacturers were and are smart. It just so happens that they design them so that the engines' maximum torque is developed at, you guessed it, close to the rated PTO speed.

Joe