So, a thought occurred to me today. HP is directly related to RPM. That is, theoretically, if you can double your RPM, and still make the same torque, you double your HP. Thing is, many “performance” engines today only rev to seven thousand or so. Why?

Basically, what is it that limits how fast an engine can operate? My first guess would be that as the crank spins faster, it needs to be more and more precisely balanced to avoid tearing the block apart. Secondly I would guess that standard spring-operated valves can’t cycle that fast, leading to “Valve float.” Hence technologies like Koenigsegg’s pneumatic valves or Ducati’s Desmodromic valves. Third guess is that above a certain speed, the friction on bearings and other contact surfaces builds up more heat than can be easily carried away. Fourth guess that just occurred to me is that it’s limited by the mass of the pistons/rods.

Are there elements I’m missing? What are the sort of things that more exotic engines do to deal with these issues that allow them to rev so high?

*preceding statements have no basis in practical knowledge and may be quite false.