Dan wrote in part:
Hopefully not a detonation. That would be like slamming the piston face with a
sledge hammer. In fact it's a rapid combustion.

Amen. Detonation is exactly what octane is designed to prevent. The higher
the octane rating, the more resistant to detonation the fuel is.

I spent some time next to 3350 cubic inch engines which could be destroyed in
seconds by detonation -- even when using 130-145 octane fuel (purple and very
expensive.) Boost the manifold pressure, haul back on the RPM -- and the
engine might actually depart from the wing in a few seconds. Not recommended.

Quent