Fuel octane?
03-28-2023, 07:17 PM
#1
Junior Member
Thread Starter
Fuel octane?
Curious to see what octane everyone runs based on climate and what seems to run best for them? I'm based in NY and have access up to 93.
03-28-2023, 07:22 PM
#2
California and 91 is it unless you get race gas.
03-28-2023, 07:26 PM
#3
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03-28-2023, 07:52 PM
#4
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Higher octane than recommended does not give you more power w/o a specific tune taking advantage of the higher octane, for example by increasing the compression ratio or boost on turbo charged engines. The octane rating is a measure of how much the fuel resists combustion. The higher the octane the more it resists, so higher octane is not necessarily better as it makes the fuel harder to ignite. The engine has to be tuned for it properly to take advantage of it.
US spec cars that are tuned for premium fuel make the rated power at 91 octane, because that is the lowest common denominator across the states. 93 isn't gonna give you more power over 91. Aftermarket software tunes take advantage of higher octane fuel to increase power, but require that you fill with the higher octane fuel. For example most tunes require at least 93. On 91, those tunes only make marginally more horsepower and you generally have to switch the map if you can't find 93 with an aftermarket tune, otherwise the engine may start to knock.
The bigger factor is altitude. When I said US spec engines make full power at 91, that's not quite true for naturally aspirated engines if you drive above sea level. Power will be reduced due to the lack of oxygen proportional to the altitude. Forced induction engines can compensate for it to some extent by forcing more air into the combustion chamber at higher altitude, but generally, engines make more power at sea level than at higher altitude.
US spec cars that are tuned for premium fuel make the rated power at 91 octane, because that is the lowest common denominator across the states. 93 isn't gonna give you more power over 91. Aftermarket software tunes take advantage of higher octane fuel to increase power, but require that you fill with the higher octane fuel. For example most tunes require at least 93. On 91, those tunes only make marginally more horsepower and you generally have to switch the map if you can't find 93 with an aftermarket tune, otherwise the engine may start to knock.
The bigger factor is altitude. When I said US spec engines make full power at 91, that's not quite true for naturally aspirated engines if you drive above sea level. Power will be reduced due to the lack of oxygen proportional to the altitude. Forced induction engines can compensate for it to some extent by forcing more air into the combustion chamber at higher altitude, but generally, engines make more power at sea level than at higher altitude.
Last edited by superswiss; 03-28-2023 at 07:59 PM.
03-29-2023, 01:44 AM
#5
Member
After some googling, I topped off with 5 gallons of 100 octane racing fuel (10$/gal!!!) which was hard to come by in Los Angeles. The check engine light was gone when I started the car, but I'm still unsure if it was actually the spark timing and am not willing to experiment. I haven't had any problems - or filled with less than 91 - since.
Last edited by 818benz; 03-29-2023 at 01:50 AM.
03-29-2023, 10:25 AM
#6
Junior Member
I have used 89 before and sometimes alternate 93 with 89. 89 octane doesn't seem to affect fuel consumption or performance. But then again I usually use 89 when I'm driving on the interstate at 70 mph on driving aids. I live in Mississippi and travel between MS and Louisiana. Warm, humid and sea-level.
