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.

[jtower1969]

I'm sorry. after re reading it...you guys were talking about the ratings in the 70's.

[TDW]

Well, that explains why the fresh, 11.2 to 1 350 LT1 doesn't like the 93 gas. We broke it in on the dyno with 110, then tried to run some 93. No go. It rattles. We played with timing and jets quite a bit, different heat ranges for the plugs. I thought the Premium, or Ethyl, back then was closer to 96 or 98. I read on a bunch of different sites that guys are running these engines on 93, so I wanted to try it. My L78 and my 302 both will run on 93, but they seem to run better when I mix the 110 with 93. Thanks for all the responses. Hope to have the engine running in the car in a day or so. Can't drive it yet because of the salt and snow, so no real hurry on it.

[COPO]

The way octane is measured has changed over time. Today's R+M/2 which is the average of the research octane + motor octane differs from the good ole days so it is not an apples and apples comparison.

[Keith Tedford]

A couple of times I got caught short and had to use some regular grade in our L72 car. Had to set the timing back just to drive it. Today, our L78 runs just fine on 91-93 octane. I've even had a fill up of 87 by mistake and ti got around ok. Mind you we don't try to run 40 degrees total any more either. I've always figured that the rating methods were somewhat different.

[3macs1]

Hey Keith, did you guys have access to Sunoco in the 70's in Ontario. It was not down this end of the country. I remember the super shell but that was about it.I was not smart enough to hold onto my square port stuff to run it today. Brother runs a 11;1 compression today as you say with no problems.Same time he might go 1000 miles a year

[PeteLeathersac]

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Thinking back it was hard to imagine but true we would go out the the airport and they would fill your drum. No problem.

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Here too, no problem at the airport and even to as recent as the late 80's we could pull the car up to the airport pumps and they'd clip the groundstrap to the bumper and fill'er up w/ 110!.

~ Pete

[3macs1]

Only In Canada Pete. Wow you had a full service air port. We had to put the drum in the back of the truck and take it out.They would not fill the cars directly. Same time one guy that worked there ran a 70 chevelle. If I hooked him when he was working the fuel was 10.00 a drum.