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Old 07-07-2005, 10:58 PM
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Running 100 Octane Gas with 9.0:1 compression

Hi everybody,

I work next to a small airport that runs their planes on 100 octane gas. Just out of curiousity, is it safe to run that gas with my current combination? Will it make a difference in performance? Can this be harmful?

Here's my combo:

350
76cc chamber heads "487" castings
2.02/1.60 valves
Edelbrock performer intake
Flattop pistons
Edelbrock cam 204intake 214exhaust .420 lift .442 exhaust
Quadrajet carb
TH 350
3.42 gears

This is in an 86 Chevy 4x4 pickup that weighs about 4800 lbs. A set of headers and a cam swap would really wake this engine up. Just too heavy of a truck to start out with for performance, but it does ok.

Anyway, probably didnt need all that info but i guess its always fun to share. Just curious if its safe to run the 100 octane. The highest we can get at the pump is 91. Thought it might be fun to fill up with a tank of airplane gas sometime or at least mix it. A guy I work with fills his motorcycle up with it for the winter cuz he claims it wont go bad like regular gas. Anyway, let me know what ya think. Thanks.

Chevy21

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Old 07-07-2005, 11:08 PM
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you can run 100 octane if you want to waste the money, your compression really doesn't warrant anything higher than 89 or 91. In fact, given that 100 octane gasoline burns slower than its lower octane kin, you'll probably make a little bit less power than you would if you just ran 91.

K
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Old 07-07-2005, 11:11 PM
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airport

We have a small plane airport in the middle of town. I was told that if you pay 20 bucks to become a member you can buy the 100 octane fuel. It is actually quite cheap because you are not paying the road tax added to fuel.
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Old 07-07-2005, 11:14 PM
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That is kind of what I was thinking. Well so much for that idea. My brother has a 4-stroke dirt bike that has 12:1 compression and there is an unreal difference from when he's running 91 compared with 100 octane. You have to hold on a hell of a lot tighter when running the good gas.
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Old 07-08-2005, 02:22 AM
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av gas

aviation gas has a higher octane rating but the properties are not made for a car engine. Airplanes run at a limited rpm range and they dont vary like a car does. the fuel is made for that type of usage so av gas is not as good as high octane "car" fuel.

With 9.1 compression and 100 octane you probably will loose power, yes you can advance the timing much more but over all you will probably make less power and economy.

89 octane should be sufficent, and with aluminum heads you could probably get away with 67 octane.


my 67 vert http://htwheelz.smugmug.com
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Old 07-08-2005, 05:45 AM
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You didn't mention which 100 octane avgas you are referring to. There are 2 of them. Generally you will only find 100LL (low lead). It's colored blue for identification. The other 100 octane is just known as 100 octane and is colored green. Most airports only have 100LL because it will work in place of standard 100 octane. Even though it's 100 octane, it still has SOME lead in it.
JA
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Old 07-08-2005, 07:14 AM
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Yeah, it is green in color.
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Old 07-08-2005, 05:55 PM
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You only want to run enough octane to stop detonation. Running more octane than will loose power and could damage your engine.

I run 11:1 with iron heads, a lot of timing, and 91 octane is fine.
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Old 07-08-2005, 10:07 PM
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87 octane just hit $2.39 a gallon here, so aviation fuel may be cheaper. LOL Hg
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