Blimey! this thread has been busy whilst I was replying...
I'd suggest that the lack of burnt exhaust valves..... YOU AGREE, Yr. Right? There are very few nowadays?
Is due to the very weak mixtures now prevalant...= lower temperatures. (Agreed, improved materials do have a part to play)
Remind me again, how do you establish the correct ratio?.....OH!YES! you lean so the cylinder head temperature is a number of degrees below the peak temperature a cylinder will develop.
Maybe , in due course, fully automatic, feedback-loop controlled ignition and fuel systems will become certified and normal for Aviation Piston Ops. meanwhile, like a 1930's car, the Chauffeur will just have to develop a "feel" for the engine and adjust the controls available , for best performance.