[oldman]

The octane limit of about 10 PSI on 93 is a good rule of thumb, there is some flex of course because we all know boost is related to restriction. So 10 PSI of boost on stock engine is not filling the chamber up as much as 10 PSI of boost on a heads, cam, header engine. Same goes for where the boost happens, 10 PSI on a twin turbo big cam engine reaching this boost at say 5500 RPM has far less detonation potential than 10 PSi on stock lt1 with a 1.7 PD pullied at 2800 RPM, there is going to be more fuel, air, and much slower piston speed, all of which contribute to detonation (charge heating too adds to detonation). Gut feeling and I don't want to test the limits here, the 1.7 PD on stock engine is about 1 psi lower than this rule of thumb and a twin turbo, large cam built engine is 2 PSI above (assuming relatively lazy turbos). That 3 PSI swing, added to better flowing build engine does equal a WHOLE lot of HP when all is said and done. .i.e 11.5 CR is octane limited, but within this limit different builds probably vary by say 70 HP or so (granted it is expensive HP).

On my 11.5 CR build, the most knock retard I've seen to date is like 1 degree and Texas can get heck of hot.. all on 93. I'm on E85 tune now.