I could be very, very wrong, but my understanding of efficiency is that 25%
efficiency means that a quarter of the energy goes to torque and 3/4 to
heat. That would mean you throw away THREE horsepower's-worth instead of
four, no?

Jim



since such engines are no more than 25% efficient when it comes to
converting the heat of combustion into torque at the crankshaft. That
means that for every horsepower measured at the crank you must
generate at least four horsepower's-worth of heat in combustion.