Not Ranked
Higher octane fuels burn more slowly. The only reason to run a higher octane fuel is if your engine detonates with more than about 20deg BTDC top-end timing advance on whatever fuel you're trying to run in it. If you run less than about 20 to avoid detonation (I don't like to see less than 26 personally), you're generating a bunch of heat out of the exhaust from all the retard, and possibly putting your exhaust valves through hell. If that is the case, then running a higher octane fuel and advancing the timing is for you.
One thing to keep in mind...if a typical Ford V8 is found to detonate at 34deg total, and run optimally at 32 total on 94 octane, increasing the octane to 104 and NOT advancing the timing will LOSE power every time. The 104 burns slower and acts like timing retard. Rule of thumb; advance .5deg for every octane point. (104-94 = 10) (10*.5)=5; advance timing 5deg from whatever the "optimal" point was on 94 octane.
And, if you're building an engine on california 91 octane mule piss, it's interesting to note that we're making the same power on 8.5:1 engines and this crappy gas with about 32-36deg total as we do with 10.5:1 engines running 20-24deg total. And, the low compression engines run cooler/happier. And...in both cases, our numbers compare to other builders/tuners across the US. Yet more information that says "octane alone does not make power".
Byron Reynolds
RACE Systems
San Jose, CA
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