why is that hard to believe? my sb2.2 heads have 33cc or 38 cc chambers cant remember exactly off hand without getting the paper work out my engine builder and i talked this over and i recall him saying 18:1 would be the most i could run on pump gas before some kind problems would come into play with my setup. so we got je involved in on this also. This is why i use torco 118 nos fuel its 120 motor octane. So Ed why dont you explain to me why I couldnt possibly have 18: 1 comp. with no power add ons?