Another thing to consider is the RPM range where the engine reaches its horsepower and torque peaks. Generally speaking, an engine should begin pulling in any gear at or just below its torque peak, and wind up to near the HP peak before shifting to the next higher gear. The Detriot diesels Grigg likes have a very narrow power band, aboutt 400-500 RPM between shifts. The Detroit, being a 2-cycle engine, sounds like it's running twice as fast as normal because the cylinders fire on every downstroke of the piston. Most Detroits have a maximum governed speed of about 2100-2300 RPM, and a minimum loaded speed of 1,750. Detroits DO NOT like to be lugged down! The Onan/Cummins engine I have has a rated speed of 3,600 RPM, with a torque peak near 1,800 RPM almost the same as a similar gas engine, so gearing isn't as much of an issue for it.
Jerry
