octane booster that is funny. even the best octane boosters only raise you octane .7 point. these engines were built back when leaded gas was still around. now the lead done several things including detonation resistance. two ways to run high compression huge cam to bleed compression and high octane race gas. 11:1 is doable on pump gas but you have to have everything tuned perfect 10.5:1 is a little more forgiving but still a little touchy just like techinspector said 9.5 is a gods plenty and the 10.5 really won't gane you that much maybe 25 horse but if you still insist on the 10.5:1 all i have to say is good luck i've been there done that and i'm sure these other guys have too.