The best octance for GT ?

no, 87 is fine... in fact higher octane fuel may actually hurt performance ever so slightly.

87 is best, UNLESS you have your car tuned for 93, then 93 will help your performance

87

This question comes up routinely, and there are a few opinions. Basically, higher octane will not hurt, but may not have any benefit.

Higher octane provides more resistance to detonation. Unless you currently see dotonation, higher octane will not deliver a significant benefit.

On the other hand, Car & Driver did a comparison in 2003 with several vehicles designed for 87 octane. They did a performance comparison with 87, drained the tank, then filled with 91 octane. Surprisingly, most of the vehicles showed measurable benefits from the higher octane. A 2003 Mustang GT was one of the test vehicles that showed an improvement on the drag strip. A Honda Accord performed worse on the higher octane. Go figure. I think the bottom line is you shouldn't expect any major benefits. But they may exist for you. I get better mileage on long trips with higher octane, and the engine seems to run smoother. The mileage (~+2 mpg) is measureable and repeatable, but I have no way to quantify "engine smoothness."


The owner's manual of my 93 Celica stated that "some detonation is normal," so if that is the case, eliminating it with higher octane can show mileage and power benefits. I don't know how common detonation is with our cars on 87 octane under "normal" conditions.

260k on my mustang after 750 miles a week every week i think ive tried every octane of fuel several times and i actually loose 1/2mpg with premium. I have NEVER experianced spark knock on 87 that i know of...

Is there any worthwhile advantage on switching from 87 to 93 for tuning purposes? My car has pretty much full bolt ons as you can see in the sig.

Do the benefits of a 93 Octane Tune outweigh the additional price in fuel? I have the default Diablo 87 tune right now but didn't really notice a difference.

Sonic04GT said:

Is there any worthwhile advantage on switching from 87 to 93 for tuning purposes? My car has pretty much full bolt ons as you can see in the sig.

Do the benefits of a 93 Octane Tune outweigh the additional price in fuel? I have the default Diablo 87 tune right now but didn't really notice a difference.

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I have the tuner set for 91 and I use 89 mostly. I don't notice a difference at all in performance between them, maybe at most 5 hp? If your car is tuned really tight then it would make a difference but other than that I personally don't see it. Maybe someone with more knowledge than myself will chime in.

Unless you're tuned for higher octance, stick with the cheap stuff.

Mustang5L5 said:

If you are stock....stick with 87


I wish in had a car that could run on 87.

I went from a v8, getting 27mpg highway on 87, to a v6 getting 25 mpg highway on 91+ octane.

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Tell me about it, Volvo says 91 is technically below the minimum the car was designed for. If i drive it hard i average 18-19mpg, if i try to save gas i get maybe 21-22.

E85