bluechip
Veteran Member
In general, lower RPM means more torque to make a certain HP, not necessarily what speed the engine will hold together at. For example, I would prefer an engine that makes 30HP at 2000 rpm over one that has to do 3200 rpm to make 30HP. This is one of the main reasons that a 30 HP diesel engine can do more work than a 30HP gas engine... chances are the gas engine will need 3600rpm to get to full HP and the diesel will make that HP at a lower speed because of its higher torque. Older, long stroke, high torque engines run at lower rpm, they can use heavier rods, cranks, etc because they don't have to hold up to the higher RPM, that does not mean it is a weaker engine, probably the oposite. Newer engines run at higher RPM, its a way to get more advertised gross engine HP from a smaller engine. Higher reving engines need less moving mass so internal parts must be made smaller and lighter...