compression ratio + pump gas

WJ nailed it.

The higher the C-ratio, the more octane it will need. The larger the cam in said engine, lower octane it will need. This is why you have guy's running 11-1 iron headed engines with whopping huge cam profiles on pump gas. Of course, huge cams require big stall, numerically high gears in order to work properly. But it'll run on 92.