comp ratio?

[auto alchemist]

ok when i went to school my teachers told me that 10.5:1 CR is about the safe limit on pump gas (93 or 94 octane), yet i see ALOT of import guys buying 12.5:1 comp pistons, and i have a friend thats running 12.5:1 knuckles in his 69 camaro with a DZ code 302, and they all claim that 12.5 is safe on pump gas.

so my question is this actually safe or are they just blowing smoke, because ive been thinking about building an N/A engine later on and 12.5 would be alot better than 10.5 if its actually safe.

[mustangboy]

From what I've read in the past you can run 11-1 up to 12-1 range on pump gas but you better have all the variables dead on. I believe alot of it has to do with quench and how effeciently every thing works together. It can be done but you have very little room for error to keep it safe.

[ibstrokin]

I've always heard 11:1, but talk to your engine builder. You may need to 0 deck your block to help quench. You would probably want to have it dyno tuned to be safe. I think factory ls1 engines are 10-3/4:1.

[cstreu1026]

I think it all varies depending on the engine design. On a SOHC 4.6 11:1 seems to be the limit. Seems like there are guys running safely at 11.5 or a little more with the 4 valve heads.