good luck to your friend. As mindgame says, it's extremely difficult to calculate al frictional losses. The most simple way is to study an old engine, the most basic one.
Just imagine the number of calculations he has to do... one cylinder, the rings, the speeds, forces involved, friction when the oil is at certain temperature...omg
then go to the crankshaft. All bearing, conecting rods, bands, chains, gears, etc involve in power losses up to a 10% in certain conditions, and not mentioning all frictional and heat losses.
for some heat losses he can consider the fuel/air ratio in the cylinder, the effectivness of the combustion, the transformation of chemical to kinetic energy....
I'm dizzy just thinking of everything, that's why it's more easy to have the theoretical input power and measure the output power
