> Do you have a source for that? You can work it out from first principles. The loud noise is a form of energy - therefore all of the sound reaching your ears

> Do you have a source for that? You can work it out from first principles. The loud noise is a form of energy - therefore all of the sound reaching your ears is energy which was produced by the engine but did not contribute towards propelling the car. > If it was true race cars would be a lot quieter only if there was some way to recover the energy from sound or prevent it from being emitted in the first place since race cars are loud we have to assume that losses from noise are an unavoidable side-effect of the workings of internal combustion engines We can see here an article from 2017 celebrating a Formula 1 racing engine reaching >50% efficiency for the first time: https://www.britishgas.co.uk/business/blog/mercedes-formula-1-engine-reaches-landmark-efficiency-target/ https://www.britishgas.co.uk/business/blog/mercedes-formula-... "The F1 cars are now closing in on levels of thermal efficiency reached by diesel engines used in large container ships..." so half the energy from combustion is lost as heat, noise etc