Octane rating is an indicator of the fuel's resistance to
predetonation (knocking). It is not an indicator of how good
the fuel is in other repsects.

Minor nit: My understanding is that you can have either "detonation"
or "pre-ignition" but I've never heard of predetonation.

Detonation is not the same thing as pre-ignition. Detonation is the
sudden combustion of the fuel air mixture, or rather the more quickly
burning of the mixture, after it has been ignited by the spark plug.
Some people call it an explosion but it really is not, it's just that
the mixture burns up so much more quickly that the piston is still
close to the TDC position, so the combustion occurs in a very tightly
squeezed area and the ringing sound you hear is the shock waves of the
very quick burning of the mixture.

Engines can stand a small measure of detonation for a very long time
before anything bad happens to them. In fact for a while, engines
were tuned such that some detonation during high pressure, low rpm was
normal and expected.

Pre-ignition, on the other hand, is always bad and VERY destructive.
Pre-ignition is when the mixture gets ignited from some heat source
(like a glowing piece of carbon or a too hot spark plug tip) prior to
the spark plug sparking. If this happens too soon, the peak pressure
point can occur while the piston is still rising in the cylinder. This
is disasterous in terms of loss of power and results in the production
of intense heat which can and has caused the very quick total
disintegration of the piston, or worse.

Corky Scott