Octane question?
Thread Starter
Drifting
Joined: Sep 2007
Posts: 1,296
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From: Forest Hill, (Out in the country), north of Baltimore. Maryland. Land of "Pleasant Living" with my Corvette, steamed crabs & crab cakes.
Octane question?
I have a 08 auto 3LS Coupe, no other options. I run Sunoco 91 octane, would a higher octane make my Vette perform faster? The highest I have seen in Maryland locally is Exxon with 93 or 94 Octane.
Race Director
Joined: Jul 2004
Posts: 16,795
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From: Lake Havasu City, AZ
Increasing octane slows combustion.
Unless your engine is tuned for higher octane and advances the timing to take advantage of it, there is absolutely no benefit to running higher octane.
Unless your engine is tuned for higher octane and advances the timing to take advantage of it, there is absolutely no benefit to running higher octane.
Safety Car
Joined: Jun 2004
Posts: 3,563
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From: Dallas Tx
Gas quality varies so much, you'd need a scanner to determine if your getting any spark knock. If your not getting any spark knock at all, then no 93 wouldn't make any more power than 91.
If you are getting any spark knock on 91, 93 will make more power.
Both have the same BTU's, just a matter of - is the motor knocking at all. If not, there is no power to be gained at a higher octane.
Vette motors are such high compression, most will show a little knock. I'd always use 93 if available. I've heard 91 rattle like marbles in a tin can. Very area specific though, I've also seen some areas where 91 runs perfect.
If you are getting any spark knock on 91, 93 will make more power.
Both have the same BTU's, just a matter of - is the motor knocking at all. If not, there is no power to be gained at a higher octane.
Vette motors are such high compression, most will show a little knock. I'd always use 93 if available. I've heard 91 rattle like marbles in a tin can. Very area specific though, I've also seen some areas where 91 runs perfect.
Safety Car
Joined: Aug 2004
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From: Lakewood WA
Not so. The ECU will pull timing if it senses knock from lower octane. I suspect it will also add fuel to kill the knock. So yes, 93 octane will yield slightly more power than 91. But I doubt you would notice the difference unless you are at the drag strip.
Race Director
Joined: Jul 2004
Posts: 16,795
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From: Lake Havasu City, AZ
You are partially correct. IF there is knock the computer does retard timing. So increasing Octane to reduce detonation (combustion) would increase power as timing would not be retarded. The LS3 engine is designed to optimally run on 91 Octane and there is no suggestion of knock. Adding Octane in the absence of knock actually reduces power. Adding fuel does not kill knock.
Safety Car
Joined: Aug 2004
Posts: 3,745
Likes: 5
From: Lakewood WA
You are partially correct. IF there is knock the computer does retard timing. So increasing Octane to reduce detonation (combustion) would increase power as timing would not be retarded. The LS3 engine is designed to optimally run on 91 Octane and there is no suggestion of knock. Adding Octane in the absence of knock actually reduces power. Adding fuel does not kill knock.
Le Mans Master
Joined: Jul 2005
Posts: 5,328
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You are partially correct. IF there is knock the computer does retard timing. So increasing Octane to reduce detonation (combustion) would increase power as timing would not be retarded. The LS3 engine is designed to optimally run on 91 Octane and there is no suggestion of knock. Adding Octane in the absence of knock actually reduces power. Adding fuel does not kill knock.
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Melting Slicks
Joined: Sep 2007
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From: READING PA
St. Jude Donor '08-'09-'10
Your last two statements are incorrect as well as the one above about higher octane slowing combustion. Octane is a measure of the resistance of a fuel to self-ignite or detonate...it is not a measure of the BTU content or the flame speed of the fuel. "Going richer or leaner from stoichiometric correct mixture (Lambda=1 or 14.7:1) decreases the probability of knock. A rich mixture is especially effective in reducing or eliminating knock because of the longer ignition delay and the lower temperatures of compression." This is quoted from my Internal Combustion Engine text book from college where I minored in ICEs.