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Discussion Starter · #1 ·
I have a completely stock 98 GTI VR6, and it seems like it runs faster on 87 octane as opposed to 93. The gas mileage is a bit less (though I havent accurately kept track), and it doesn't warm up as smoothly in the cold - but I'm pretty sure I can feel more acceleration with a lower octane.
This could just be placebo effect, but I know that octane resists combustion and higher octane fuels burn slower than lower octane which might explain this. Any thoughts or similar observations?
 

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Re: Car runs faster on 87 octane? (4thChirpinGTI)

one thing for 2.o users.... Never put anything other than REGULAR if you are running stock...
 

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Re: Car runs faster on 87 octane? (bookpublishar)

Quote, originally posted by bookpublishar »
I have a completely stock 98 GTI VR6, and it seems like it runs faster on 87 octane as opposed to 93. The gas mileage is a bit less (though I havent accurately kept track), and it doesn't warm up as smoothly in the cold - but I'm pretty sure I can feel more acceleration with a lower octane.
This could just be placebo effect, but I know that octane resists combustion and higher octane fuels burn slower than lower octane which might explain this. Any thoughts or similar observations?

I don't know about making it faster, but it sure does make it run a little better. As soon as I got my car, I started putting 93 octane in it and it ran great http://****************.com/smile/emthup.gif And higher octane gas is supposed to last you longer...bring your gas mileage down. http://****************.com/smile/emthup.gif
 

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Re: Car runs faster on 87 octane? (MigAce312)

it could be a timing thing. With a lower octane your motor will be firing a little sooner because the flash point is lower. That may be what your car runs best with in conjunction with the set of the ignition timing.
IMO keep using 87 then, save yourself some money.
 

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Re: Car runs faster on 87 octane? (rednekdubbin)

better- yes, faster- i highly doubt. vw recommends using 93 octane, but whatever its your engine.
 

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Re: Car runs faster on 87 octane? (VeeDubster411)

Quote, originally posted by VeeDubster411 »
better- yes, faster- i highly doubt. vw recommends using 93 octane, but whatever its your engine.

the best i can get here is 91

the cheapest is 89, so thats what my car drinks

stupid college tuition
 

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My supercharged 2.0 seemed to run better on 93 then 94, I wonder if it was because the "flash point" was lower and there for advanced timing just a little for more power. I say keep running what VW recomends no matter what 'feels' better.
 

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Re: (vwtuning)

it could have alittle bit more power if you went to a lower octane because it burns faster.. The higher the octane the slower it burns, thats why its good to put it in your car when your chipped/turbo'd/Supercharged is so that when you have aggressive timing or a factor like air being forced into the cylinders it is easier to prevent detonation when the explosion isn't as fast.. And I was under the impression that when you ran lower octane that it retarded your timing alittle to prevent detonation and when you had higher octane it advances timing.. Thats basically what a chip does (advances timing) and thats how gains are made from a chip
.. Doesn't make sense why it advance timing with crappy fuel
 

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Re: (MunKyBoy)

The gist of the way octane works has been outlined in this post, but to really understand why you may have more power consider the physics of hydrocarbon fuels...
The octane content is the % of fuel based on octagonal (8 element) molecules of fuel. Octagonal molecules are much more stable than any other atom formation.
The higher the octane percentage, the more resistant the fuel is to unpredictable detonation (early detonation)
Cars with higher compression (forced induction, high compression race engines) require a fuel that is more stable to prevent early detonation caused by pressure in the chamber rather than a spark from the plugs.
The VR6 is not a super high compression engine (10:1 stock), however vw does reccomend 91 octane due to other factors, like the arrangement of the cylinders and the way the stock timing is set up.
Early detonation caused by using fuel not stable enough may have the feeling of more power the engine's timing may be unpredictably advanced. In the VR6 dual knock sensors will eventually retard timing to compensate.
Proper stability fuel (91 or above) may feel slower because its' actually more predicatable and detonating only when timed to do so by the ECU and ignition system.
I claim to be no expert in the area, but that is my limited understanding of the way hydrocarbon fuels work in combustion engines. Feel free to chime in and correct or re-word what I may have misconstrued.
It is also worthy of noting that when you see race fuels with octane ratings of 100 or above, they are obviously impossible according the explaination I've given (how can you have 104% stable fuel?). Technology has allowed the creation of artificial fuel additives that further resist detonation. These artificial non-natural occuring additives allow fuels to be rated more stable than 100% for use in race engines.
HTH
 
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