What cam are you running? Have you checked the DCR (dynamic compression ratio) which gives you a more accurate picture of your engine's compression that static compression ratio? You can go to the Keith Black website and use their calculator. You will have to know your cam specs, your head gasket specs, combustion chamber size, pistons relief in cc's, etc. For use with pump gas, you ususally figure a maximum DCR of 8:1 for iron heads and 8.5 for aluminum heads. My static compression is 10.6:1 but with the cam I chose, I have a DCR of 8.46:1. I have no problems running 93 octane. To run less octane, you need to lower the DCR.