I'm a mechanical engineer so feel free
Yeah I understand that friction and energy loss will change with different gears. But in the same gear at the same engine speed with lets say a few small bolt on mods that add 10bhp those mechanical losses aren't going to change. different when you start looking at forced induction because increasing boost will mean more air in the cylinder so more energy is used to compress the charge but these changes of a few psi in the chamber (I would guess) are insignificant compared to frictional losses from the drive train which in this example would remain unchanged. Unless of course you are doubling the boost or something but then you are looking at major modification work to all aspects of the engine and drivetrain so comparing losses to standard becomes kind of irrelevant anyway.