Compression Ratio vs Octane Table?
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Compression Ratio vs Octane Table? (lead_foot)
Octane sensitivity is possibly too complex for a simple table.
It depends on head design, quench area and other factors controlling charge swirl along with CR. For example, if you went to a thinner head gasket, reducing quench, you would likely reduce octane sensitivity even though you would have a higher CR.
It depends on head design, quench area and other factors controlling charge swirl along with CR. For example, if you went to a thinner head gasket, reducing quench, you would likely reduce octane sensitivity even though you would have a higher CR.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: Compression Ratio vs Octane Table? (lead_foot)
Yeah it depends on alot of things. What combo do you wish to run?
Generally more than say 11-11.5:1 is too high for pump gas.
Generally more than say 11-11.5:1 is too high for pump gas.
Thread Starter
Racer
Joined: Jan 2002
Posts: 341
Likes: 1
From: Cave Creek AZ
Re: Compression Ratio vs Octane Table? (65Z01)
What I'm trying to do is get an idea of what the max (I realize that this could be off a little one way or the other) static compression ratio I could run in an L98 using 100 octane unleaded fuel. Just an estimate would be fine. Are we talking 11.5, 12, 12.5, 13 as a guess? If and when I actually head down this path I will work with a qualified, professional engine builder to make any final decisions. :)
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Compression Ratio vs Octane Table? (lead_foot)
Lingenfelter states that with Al heads 10.2:1 will run comfortably on pump gas, and that's with no mention of techniques to reduce octane sensitivity.
Pro
Joined: Jan 2001
Posts: 681
Likes: 2
From: Newton (Wichita Area) Kansas
Re: Compression Ratio vs Octane Table? (AS84)
in an old setup on our ford 422 I ran 12.3:1 at 36 degrees advance with no detonation on 93 octane.
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Race Director
Joined: May 2001
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Re: Compression Ratio vs Octane Table? (lead_foot)
A friend of mine built a 396 that was supposed to be running around 12.5:1 compression and it didn't have any audible detonation. That doesn't mean the computer wasn't pulling timing, but if it was it wasn't pulling much because it ran like crazy. However this was on an LT1 and I've heard that the reverse flow cooling has a lot to do with it. The cooler cylinder heads are probably what allowed him to get away with it.
Melting Slicks
Joined: Aug 2000
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From: Springfield MO
Re: Compression Ratio vs Octane Table? (jmr302)
in an old setup on our ford 422 I ran 12.3:1 at 36 degrees advance with no detonation on 93 octane.
Was this with aluminum heads? I'm running Dart Iron Eagle heads with 11.2:1 compression. It detonates with 93 octane and 33 degrees advance.
Was this with aluminum heads? I'm running Dart Iron Eagle heads with 11.2:1 compression. It detonates with 93 octane and 33 degrees advance.
