High Altitude Octane: 85 vs 87

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Aug 27, 2002 | 07:41 PM

sagjohnson

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High Altitude Octane: 85 vs 87

My 87.5 CGT calls for 87 octane, as well as my 89 100q. I live in Utah, up in the thin air. Have been told that running 85 would be okay because of this. I'm currently trying this. The engines seem to be okay, but I can't be sure.

Anybody out there KNOW the answer. My altitude up here is about 4,600 ft.

Aug 27, 2002 | 08:41 PM

CGTBrad

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got me... I always run the highest octance I can afford

95% of the time it's 89 down here at 200 feet above sea level... Am I off base with this. It was my understanding that these engines run a lot better on high octane...

Aug 28, 2002 | 08:30 AM

4kq

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Heh,

That is the max octane in S.Utah...lol.

85 is fine with the stock timing, it is a low compression engine (I-5 8.5:1 right?) I would get the next grade up and advance the timing. That works really well at elevation with my JT engine. You can hear it knocking with the window open.

Aug 28, 2002 | 12:13 PM

furiousgeorge

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Re: got me... I always run the highest octance I can afford

I think I remember from a road and track dated 1986 or 87, a 1986 4000S ran 89, but would also run 87 well enough. Looking inside my fuel door, it (as all german words do) screams OKTAN 91. I use 89 octane with outlaw octane booster, which is pretty strong stuff, 3.5oz for a full tank, burned a hellofa lot of carbon out of the engine when I first started using it.