Compression

There are a number of factors that effct how much compression you can run for a given octane rating.

1. The amount of duration in the cam shaft. It's the cylinder pressure that is important not the static compression. A cam with 300 degrees of duration will bleed off a lot more cylinder pressure than a cam with 200 degrees of duration. This is why putting a long duration cam in a low compression motor kills off low rpm torque.

2. The design of the cylinder head. A head that creates a lot of turbulance in the cylinder is much more detonation resistance. The more modern closed chamber heads with a zero deck flat top piston will allow a much higher static compression ratio.

3 The material of the cylinder head. Aluminum heads draw heat away from the combustion chamber much faster than iron making them more detonation resistant. With aluminum heads you need to run almost 1 point more in compression to be equivalent to iron heads.

4. The tune-up. Less agressive timing and richer mixtures are more detonation resistance allowing higer compression.

All of these items need to be factored into how much compression your engine can have.