question on Octane
08-25-2006, 09:34 PM
#3
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I am stock, (firehawk) and have run mid grade a couple of times no problems. I have to mix 93 with 89 to get close to the 91. Had a 2002 transam auto (stock) that the wife ran mid grade all the time , no knocking.
08-25-2006, 10:09 PM
#4
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Well I suppose technically you can. The computer will retard the timing when it hears a knock, my lt1 caprice requires premium also as per the manual, but I run mid grade all the time and it doesnt knock. My camaro has a 10.8:1 comp, whereas stock is what 10.5:1 the same as LT-1s I think.
08-25-2006, 10:35 PM
#5
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You can run 87 if you would like, but like stated above the computer is just going to retard the timing and your going to lose power. its not that much more expensive to get 91 octane. its usually $3 more for every 10 gallons so just spring for premuim.
08-25-2006, 10:42 PM
#6
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for giggles i ran 87 octane. not good. it knocked pretty bad under load. i basically did it to prove the wife wrong. use the cheap gas save money she says. ha. use what the manual says if it needs 91 or better.
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08-26-2006, 01:10 AM
#8
Originally Posted by Cld069
You can run 87 if you would like, but like stated above the computer is just going to retard the timing and your going to lose power. its not that much more expensive to get 91 octane. its usually $3 more for every 10 gallons so just spring for premuim.
08-26-2006, 02:00 PM
#9
Originally Posted by irnbru83
so does using 93 affect the timing also since it will detonate at a different point from 91?
we don't even have 91 in texas.
we don't even have 91 in texas.
Nope. The stock computer programming is optimized for 91 octane from the factory.....meaning the base timing they used was set while running 91. You can put 93 octane in, but the car will not pick up any additional power because the computer can not add more timing over what was set in the factory tune, it only has the ability to reduce timing when the knock sensors pick up detonation.
Moral: Use 91 or higher. Anything less will induce spark-knock (even if you can't hear it) and the pcm will pull timing, reducing power. Anything over 91 will not add power, as octane rating is nothing more than the fuel's ability to resist combustion.
09-14-2006, 03:37 AM
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Originally Posted by jmm98LS1
Nope. The stock computer programming is optimized for 91 octane from the factory.....meaning the base timing they used was set while running 91. You can put 93 octane in, but the car will not pick up any additional power because the computer can not add more timing over what was set in the factory tune, it only has the ability to reduce timing when the knock sensors pick up detonation.
Moral: Use 91 or higher. Anything less will induce spark-knock (even if you can't hear it) and the pcm will pull timing, reducing power. Anything over 91 will not add power, as octane rating is nothing more than the fuel's ability to resist combustion.
Moral: Use 91 or higher. Anything less will induce spark-knock (even if you can't hear it) and the pcm will pull timing, reducing power. Anything over 91 will not add power, as octane rating is nothing more than the fuel's ability to resist combustion.
guess i've been paying more than needed haha 
09-14-2006, 03:37 PM
#17
like Cld069 said.... ull only save 2 or 3 dollars. id spend the few dollars to keep my engine running strong all day. better safe than sorry is what mom always said right?
09-14-2006, 03:54 PM
#18
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Originally Posted by jmm98LS1
... as octane rating is nothing more than the fuel's ability to resist combustion.
09-14-2006, 04:47 PM
#19
Originally Posted by Black Z/28
Shouldn't it be detonation, or pemature Detonation? Or can combustion be used interchangeably with detonation?
combustion = the air/fuel mixture has been ignited
detonation/ping/preignition/spark knock = premature combustion of air/fuel mix in the combustion chamber (ie before piston gets to tdc) which can cause engine damage
what I said was octane is a fuel's ability to resist combustion....meaning a higher octane fuel is harder to "light off" than a lower octane fuel.
09-14-2006, 05:33 PM
#20
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Both premature combustion or preignition (the same), meaning that combustion occurred before the spark in a gasoline engine or detonation, meaning that the combustion process occurred out of control, will cause ping or spark knock (the same). We usually begin the combustion process well before TDC, especially at light loads. There is no difference in the ability to ignite different octane pump fuel when formulated for a given climate and they burn at the same rate, just that higher octane fuel has additives with more ability to resist detonation. High octane race fuel may be more difficult to ignite due to higher vaporization temps.