Octane rating..Circa1970

[3macs1]

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Av gas is wrong for use in a car. It is designed to run at a constant RPM...around 3500 or so. The specific gravity is also diffrent than what is needed to run on land. I was told by Rockett that Sunoco 260 would be about 95 octane by todays test methods. I run 3 or 4 gallons of 110 to a tank of Sunoco 93. (Please note it is illegal to run leaded gas on the street) Not that I would ever do that
The Rockett website has alot of information under http://www.rockettbrand.com/technicals/bulletins.htm

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Oh I'm sorry I thought we were talking in the 70's. See back then we didnot have access to racing gas so we used avgas since it was 1/2 the price and no tax.As did every other racer I knew in our area. The SG you mention was actually the different distillation curve to ensure the plane would not experience vapor lock.
We discovered to over come this and not fry your engine on initial acceleration we would mix it 35/65,rejet the carb and slow down the spark advance. You knew if your combination was right if the car would start like normal. If it became hard to start you had too much avgas in the mixture. Then no problem and no spongy acceleration.
I think the use of leaded gas actually became a federal crime in 1995 however if you go to our local airport today the small prop powered air planes still use the leaded product.