Speed is irelavant if the burn is contained in the chamber as the valve is closed. Same as the inlet. It made of a different material but as it's no open to the gas flow it dose not get effected.
When the exhaust valve opens it gets all hot gas if it still burning as it passes the valve it burns it. Not that hard really. And if you get a carbon under the seat it can cause it to burn as we'll as in correct lift timing of the cam (not meaning an aircraft engine).
Don't believe me about flame front. What happens when you do a mag check. These are big bore engines
So do you own your own aircraft.
Cheers.