no its not a fixed number, and its not a fixed percentage either. some people's cars may lose less hp through the drivetrain than others. i hear that our cars lose about 18% through the drivetrain so thats what i use. atx's are more.
say you have 100 hp at the crank, so you have ~ 80 whp, which is a 20 hp loss.
now lets say you have 1000 hp at the crank, so you have ~ 800 whp, which is now a 200 hp loss.
so no, you dont loss the same amount of hp.
