Neil it depends on the quality of the fuel available. Do you guys in Canada have the same problem as us with the ethanol added to the gasoline. It's a cap shoot to know what the actual octane rating is from station to station week to week. As far as compression ratio. 9:1 should be fine with slight variations in the gasoline. Back before they started with messing with gasoline I had no problems running 72cc heads and flat top pistons on 93 octane. I was having problems in yesterday's heat with 91 octane. I was told that this stuff boils at 100 degrees now. My fuel pressure was up and down by 3lbs. But that's another thread.
