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What is the highest compression ratio for 91 oct.

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Old Jan 24, 2007 | 09:22 AM
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Default What is the highest compression ratio for 91 oct.
A general question. No knocking and other related problems, what would be the limits of 91 octane in terms of compression ratio, 11:1? 11.5:1 or 12:1?
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Old Jan 24, 2007 | 11:25 AM
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Originally Posted by ss dave
A general question. No knocking and other related problems, what would be the limits of 91 octane in terms of compression ratio, 11:1? 11.5:1 or 12:1?
Isn't a big factor where you live? Temperature-wise? Like south Florida in the summer or Michigan. I thought the hot temps would cause detonation if the cr is too high.


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Old Jan 24, 2007 | 11:27 AM
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Originally Posted by ss dave
A general question. No knocking and other related problems, what would be the limits of 91 octane in terms of compression ratio, 11:1? 11.5:1 or 12:1?

11:1, but I'm sure you're going to get people contesting me on that.
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Old Jan 24, 2007 | 11:34 AM
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It depends much less on static compression and more on Dynamic compression. You need to get your cam specs and plug them as well as your combustion chamber cc's piston valve reliefs(if applicable) etc into a DCR calculator and find out where you are at. I have heard anywhere from 8.5-8.7 is the max for 91 octane. I am shooting for something like 8.6 for my build.
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Old Jan 24, 2007 | 07:58 PM
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How about 11.25:1 in a LS7 with a cam of 230/240/114, 70cc size chamber?
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Old Jan 25, 2007 | 09:01 AM
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I Have 12:1 In My Car. Used 91 Octane W/no Problems
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Old Jan 25, 2007 | 09:04 AM
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Greatly depeneds on alititude. In Denver, 5200ish feet, I ran 12.5:1 on 91 without a single problem. Once the car went lower in altitude, higher octane gas was a must.

Keith
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Old Jan 25, 2007 | 10:18 AM
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Wow 12.5:1 thats tight! I'm roughly at 3200 fasl so I guess 11.25:1 would work ok. Thanks
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Old Jan 25, 2007 | 12:59 PM
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I'm at 11.1 and run 91 Octane. I do throw in some octane booster when I'm going to go race just to be safe. It's all in the tune.
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Old Jan 25, 2007 | 01:19 PM
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Im 12.5 on CA 91, but then agian I have ~17* overlap at .050 so alot of that compression bleeds off
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Old Jan 25, 2007 | 02:29 PM
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im 11.5:1 in Florida and run 93 octane with no probs
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