"tony sayer" wrote in message
...

JOOI where is this other energy wasted in heat or emissions or a combo
of both?..

Pumping losses which turns into heat in the engine and exhaust. The IC
engines more a heat engines as it creates more heat than turning motion.

The best you will ever get is around 50%. That is a two-stroke diesel
running at a constant speed and constant load. In road vehicles

Suppose I have say a 100 kW engine then 25 % of that is useful driving
the wheels energy, so where would or does the other 75 kW go to then
surely not all as heat?..

Yes.