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Old 12-29-2010, 01:44 AM   #1
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Will putting a 102 or 103 octane in my z compared to 87 make a difference or not unless its tuned?
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Old 12-29-2010, 02:13 AM   #2
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Will putting a 102 or 103 octane in my z compared to 87 make a difference or not unless its tuned?
1) Your engine was designed and factory tuned to perform its best on premium fuel (91-93 octane). 87 will not yield the best results.

2) Going to 100+ octane fuel on a well maintained and properly functioning stock engine will only reduce power and mileage. Higher octane itself does NOT equal more power, only greater resistance to detonation. The object with fuel is to always use the lowest octane possibile that will still fully prevent detonation. Once you go beyond that point, you are only hurting power and efficiency.

Going beyond 93 octane in an LS1 should not be necessary unless you raise compression, add forced induction, or build a setup that likes/needs a more aggressive timing curve.
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Old 12-29-2010, 04:43 AM   #3
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1) Your engine was designed and factory tuned to perform its best on premium fuel (91-93 octane). 87 will not yield the best results.

2) Going to 100+ octane fuel on a well maintained and properly functioning stock engine will only reduce power and mileage. Higher octane itself does NOT equal more power, only greater resistance to detonation. The object with fuel is to always use the lowest octane possibile that will still fully prevent detonation. Once you go beyond that point, you are only hurting power and efficiency.

Going beyond 93 octane in an LS1 should not be necessary unless you raise compression, add forced induction, or build a setup that likes/needs a more aggressive timing curve.
well said
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Old 12-29-2010, 08:13 AM   #4
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I did try high octane in mine once at the track. I did not think it would make any difference and I was right.
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Old 12-29-2010, 09:09 AM   #5
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100% right on my old 400 GTO tuned for 89 octane ran 13.0X. same when tuned for 94. 110 octane ran 13.3
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Old 12-29-2010, 10:21 AM   #6
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Will putting a 102 or 103 octane in my z compared to 87 make a difference or not unless its tuned?
ODBII PCMs have in unmodified form 2 tables which is used for Low Octane and 91-93 Octane. Using 87 will put you in that lower range and hence less power is made. A common trick for tuning so that you do not dip back into the Low oct. tables is to make them equal/same. BUT now you can NOT use 87 anymore as there is no real fail safe for insufficent octane. Pinging/Detonation is likely to occur.

I am assuming the 102/103 is a Unleaded Race Fuel. In most cases when Octane is higher then what the car is tuned for, performance may decrease. In every case your not taking advantage of the better octane. UNLESS your are already having Knock Retard issues, then at best the car will treat it like running 93 octane, but you need so many miles/driving time for the PCM to decide it is ok to switch to the High octane tables.

As for old school non EFI setups, having higher octane wont really hurt as most have heat soaking issues and the ability to better "tune" on the fly maybe a good thing. As in the example of the Poncho 400 in that GTO.

Also to mention, for those looking at c116 or a fuel in that range, compression plays a big part of it and really in order to take advantage of that, you need a C/R that is well beyond the safe limits of Unleaded "Street" fuel.
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Old 12-29-2010, 11:43 AM   #7
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As for old school non EFI setups, having higher octane wont really hurt as most have heat soaking issues and the ability to better "tune" on the fly maybe a good thing. As in the example of the Poncho 400 in that GTO.
Currently the SBC in my Nova has '73 head castings @8.5:1 compression. With timing at 36 this engine performs its best on 87 octane, going higher makes it feel less responsive/less crisp. The old engines won't benefit from higher octane either unless they actually need it (high compression, aggressive timing, etc.). However, you do have to be more careful with the old carbed stuff, since there's no PCM to reduce timing if detonation starts to occur. I'm only able to get away with such low octane because of these low compression heads.
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Old 12-30-2010, 07:38 PM   #8
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^What he has said, depending on the blend of race fuel it can harm your o2 sensors, my bonehead buddy put some 110 octane leaded fuel in his 99z28 and o2 codes came on within 10 minutes of driving.
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Old 12-30-2010, 07:38 PM
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