Barton knows way more than I, but i would have put that at 11.25:1 on Michigan pump gas. I ran a 408@11.25:1 on 93 on the street and the track and now a 511@12.5:1 with 1 can of 110/113 Dragon and 2 cans 93 Sunoco mixed makes about 101 octane and works real nice. When the 511 was 11.25:1(200psi cranking) i also ran it on 93 pump gas(175 cranking) without an issues, so was just making a suggestion, but i understand where your at with that. Piece of mind is worth alot.