If you use iron magnum heads and set it up to get a tight quench and a normal sized mild performance cam, 10 to one compresion can run on 87 octane. With aluminum magnums and tight quench you can run 11 to one on 87. I run 10 to one compression and a stock 2bbl cam and I can get away with 91 octane. Any decent performance cam will alow you to run 87 because it bleeds off cylinder preasure. Also if you are willing to run premium fuel you can bump the compression even more and that will help MPG enough to offset the cost, that is why I built my engine the way I did.

Another thing about the "smog" heads is they have really bad combustion chamber desighn, the magnum has one of the best the differance in chamber desighn can make up to a point in compression tolerance, meaning a 10 to one magnum will be no more likely to knock than a 9 to one "smog" head.

There have been several tests between the best smog head, the 308, and the magnum and with the same motor the magnum head consistantly makes about 25 hp more with no other changes.

Don't be afraid to run 10 to one with a magnum style head.