Thicker head gaskets/ less compression...
RustyRatRod,
Compression is heat.
You can run aluminum heads at a higher compression ratio and have the same -heat in the cylinder -as a lower compression steel headed engine because steel retains heat more then aluminum.
The compression ratio is what it is.
How much:
-Air-Fuel-Pressure-Heat = Octane required to prevent pre-ingnition.
Low octane gas---------:rolleyes: lol