ShyT,
Thanks for pointing out the detonation problem, I'd completely forgotten about that! Shouldn't be too difficult to overcome, though - just replace the pistons with recessed pistons, or use shorter con-rods, to decrease the compression ratio if it turns out to be necessary. Or, if you don't want to tear the engine apart, put a spacer between the cylinder and the head.
I think it will actually be less of a problem in high-performance engines, because they are turbo-charged. I know very little about turbo-chargers in aeroplanes, but going on my knowledge from cars, the only thing which would be required would be to open the wastegate slightly.
As for your other points: I have never heard that lower octane fuel is more susceptible to vapour lock than higher octane. If that is the case, though, a bigger fuel pump should fix it?
And valve seat recession can be easilly cured using hardened valve seat inserts, exactly the same as it has been in hundreds of thousands (if not millions) of classic cars.
I'm sorry, but I really feel that some people are looking for a problem where there isn't one. And it is certainly in the interests of the engine manufacturers to do this. All piston engines are pretty much exactly the same - it's just that some are more tuned than others. And the lower the ocatane rating, the less you can tune the engine. Aviation engines are typically not very highly tuned anyway, because reliability is more important than performance.
I think I will post a link to this thread on the Tech Log forum. I can't speak for anyone else here, but most of my engine knowledge comes from car engines, which are not aluminium, so there could well be some issues I'm not aware of. It would be good to here from someone with some real expertise in this area.
FFF
--------------