[nickarules6493]

hey i have a automatic v8 4.6l gt and i run 81 octane in it now but i want to run 91 octane what are the steps i should do before i do this? i dont want to hurt my car.

[2Manystangs]

fill it up and go...it won't hurt it

[Hood Time]

Your engine was designed to run on 87. There's no benefit in running 91. You may even lose a smidgeon of power if you do.

If you're dead set on running 91, get a tuner programmed for 91.

[nickarules6493]

Originally Posted by Hood Time

Your engine was designed to run on 87. There's no benefit in running 91. You may even lose a smidgeon of power if you do.

If you're dead set on running 91, get a tuner programmed for 91.

thats what im hearing. how would i go about tuning it?

[2oo5GT]

+1, 91 will do nothing for performance unless you are tuned for it. Can actually hurt rwhp and if you have cats, the unburned gas can actually crap them out.

If you are stock, don't even both with a tune and 87 is fine. When you start buying/installing mods, then I would call a local mustang tuning shop around your area or maybe go with www.americanmuscle.com and buy their Xcal3 with a bama tune. Since you are N/A, won't be as hard to do a email tune vs if you had a power adder.

Also, 87 has a better burn rate than 91 or 93. Why some people think it's good to give their car "some of the good quality stuff" is beyond me. Now the S197's with VVT, it's been dyno proven that if you go from 87 to 93, you will gain some rwhp. But 2004 and older...no.

[racin366]

Originally Posted by 2oo5GT

Also, 87 has a better burn rate than 91 or 93. Why some people think it's good to give their car "some of the good quality stuff" is beyond me. Now the S197's with VVT, it's been dyno proven that if you go from 87 to 93, you will gain some rwhp. But 2004 and older...no.

Not exactly. Octane is an inflammable compound, the higher the octane the SLOWER the fuel burns. So 87's burn rate is not as good, but faster. Too fast and you get detonation. On an engine with higher miles detonation will be more likely because of deposits, etc. You will benefit from higher octane, how much depends on the condition of your engine and if it has been tuned for it, but all that aside, lower octane fuel is also less refined. As in more dirty. Pure gasoline is clear, like water, 87 is yellow because it has a lot more garbage in it. One of the first rules of engineering: GI=GO.

[Hood Time]

If you find that your engine now "requires" higher octane to avoid detonation, then you need to resolve the issue rather than band-aid the problem with higher octane. You'll be down on power and efficiency until you do.

As for 87 octane being more dirty, hmmm...