If you've got flattop pistons with no reliefs, zero deck height, .039" head gasket and 64 cc chambers, you're at 11:1.
Detonation can sound like the valves are rattling under acceleration. This will ruin your engine quickly. You need to run 93 unleaded, reduce your total timing to 30-34 degrees BTDC, set your base timing to 8 to 10 BTDC. Run a 160 degree thermostat, jet your carb until the plugs turn dark tan, and use a plug that is one heat range colder than stock.
If these tuning tricks don't eliminate the detonation, you'll have to either run 100+ gas or reduce the compression. If you continue to retard the timing trying to eliminate the detonation, you'll kill all the high-end power in the process.
The conventional wisdom I've heard is that a SBC can run 93 octane with a street cam until about 10.2:1 compression. Then you're looking at having to mix the grape juice or av-gas with 93 pump fuel. Parts store octane boost is NOT enough.
Severe preignition or detonation will melt the piston tops, break rings and pound out your rod bearings. Examine your plug insulators after a hard run. Any small blobs of metal stuck to insulator or electrodes are bits of melted piston. Not good.
I've seen 327s where the detonation was severely hurting power, so the owner advanced the timing, thinking the engine needed more spark lead. It flew to bits shortly after.
good luck
chip
