93 octane or higher. Running 305 heads??
if you want to make the good power your gonna have to run race fuel, like at least 110. dont think i'd even try it on 93 even if you back the timing off
agreed, with 13:1 yer gonna need some serious octane if running any sort of advanced timing. My 8.5:1 compression ratio needs 91 with 12 BTDC
All right guys. I built a 355 sbc with 13.5:1 compression. It was built for 100 octane race fuel. A 12:1 High performance SBC only requires 91 octane. A stock SBC runs between 8:1 and 9:1 and uses 87 octane. If anyone needs more info on how octane works, I can let you know. Higher octane does not always equal more horsepower. It has to be balanced with the build of the engine. He can run 93 octane along with slightly turning back the timing. That is all I did for mine for street use. Entirely different story at the track. It would be happy at 100 octane.
It all depends on timing and fuel mixture dude, my pontiac won't run 89 or 87 without pinging at full throttle, and I'm running 8.5:1. If I back off the timing to 10 or 8 BTDC, then yes, I can run lower octanes. 13:1 at 12 degs is going to ping/detonate on lower octane fuels (93 or lower). going to 6 or 4 would alleviate it but not take it all out necessarily. Octane will not necessarily give you more horsepower, but it'll certainly keep an high compression engine from spitting out a headgasket or melting a piston. If you richen the mixture, that will also quench the heat and therefore detonation, but again, power will be down as a result. A properly tuned engine at 13:1 at 10-12 degs is going to need more than 93.
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