10.5 Compression Ratio on 91 octane???
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10.5 Compression Ratio on 91 octane???
I'm going to be doing a h/c swap on my 99 vette. I'm replacing the stock heads with cnc ported LS6 heads, which should raise the compression ratio from 10-1 to 10.5-1. Now in Canada every gas station only carries 91, but only Sunoco carries 93. Can I still run 91 octane with 10.5, or do I need to start feeding it 93 octane? I ask my tuner and he doesn't recommend running 91 with 10.5 compression. But my car usually runs on Shell 91 octane.
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There is an ideal crankshaft angle where maximum cylinder pressure translates into the most power available. Ignition timing is nearly always shown as advanced because of the time the combustion event takes from the moment of ignition, past TDC to the point of maximum power transfered, and continuing as the piston moves down the bore.
Lowering the octane does change the burn rate, which will require you to remove timing (assuming it was optimized at the higher octane). Pretty soon, you are trying to hit a moving target.