Lemming,
Octane is the resitance rating of a fuel to ping or pre-ignite. Detonation is a different problem and can be a problem at any compression ratio, and higher octane fuel doesnt usually do any more than "take the edge off" rather than stop it entirely. Compression ratio is usually meaning the static ratio of the difference in swept volume of one cylinder. That's the "10.5: TRW pistons) and such you always read about. But, there's really 3 compression ratios. First is what the piston is designed to make when it's installed per the manufacturer's spec'd block deck height and the factory spec'd chamber size with no valve jobs done. I call that catalog compression. Then there's the true static compression ratio, which is what one gets when the parts are all machined and together and you take measurements. This is the real static ratio and typically is dependant on your machinist. Some are in reality, most assume catalog reality is fine with whatever they cut the deck to and whereever the cylinder head volume was. Now neither of these really mean much to a running engine. Becuase it's all only concered with the volumes of the swept area. (That's the volume of the space the piston moves thru assuming the cylinder is sealed from start of motion up to end of stroke in case that was not understood. But while the piston is moving the cylinder is not sealed. That's because at some point the intake valve closes, and that event seals the cylinder. The larger the performance cam, the later the intake valve closes. Meaning if you have more duration then it hangs open for longer and while it is hanging open and closing the piston is moving up. So that one is called dynamic compression and THAT is the key for what octane you need. That's why the cam is crutial. Higher static+smaller cam = too much low rpm cylinder pressure and detonation/ping issues. Hi static+bigger cam with more duration=less cylinder presure at low rpms and less tendency to ping or detonate.
