Depends on the combustion chamber. There's a guy over on the Hamb who has an early Hemi. He's running 13:1 on pump gas. The Hemi chamber is very detonation resistant to begin with, plus he has everything else "just right". I cannot remember his screen name, but there's a member with a butterscotch Demon who runs up in the 11s on pump gas. Yes, small block and iron heads. It can be done, but it's alot of work to get there.