This is the point that makes all of the miserable noise pollution from modified cars so much more grating, knowing that whatever is making excess noise means potentially useful (in a performance sense) power is escaping as sound somewhere in their drivetrain, so insofar as their objective is to make their vehicles loud for the sake of loud, these people are achieving the opposite of what they're trying to signal they're achieving.
Efficiency and power are not equivalent. All you need to do is look at the most powerful (hp per liter) cars and the exhaust systems they use for proof.