TUGGER

My owners manual says my car was made to run with 87 Octane, does this mean 91 Octane is bad for it???

blike

No, it just means you won't hurt your car by running 87. You can run higher octane than made for, but not lower.

billybix76

Nope. but the factory Tune is set up to run 87 octane (burns faster than 91) with the stock air intake and filter. If you run on 91 you may get slightly better HP or mileage but it also, depending on the individual car, might cause the opposite. Mostly you will be wasting money. If you want the benefit of higher octane performance and fuel economy you must re-tune your mustang to run with the exact combo of air intake/ tune and higher fuel octane. To get a better tune do the time and research on this forum the FAQ section on tuners and tunes...you wont be sorry.

Most of the time reatilers "91" octane is slghtly diluted or not even actual 91 octane but just a mix or only 87. You wont be able to tell from the pump. drive a tankfull to see if you notice anything.

TUGGER

I have the SCT Xcal tuner and have both 87 and 91 tunes I can use. I just was wondering if the manaul was saying I should only use 87.

Thanks

billybix76

Ive been running 91 Octane tune from Brenspeed for months. Love it. and no problems. Even been able to push timing a little 0-2000 at +2. No detonation on the xcal capture charts.

rmays06

Use what ever gas you the tune is set for. If you have a 91 tune its advisable to use 91octane, it could really mess things up if you don't. If you have a 93 tune use 93 gas etc....if you read the manual and it is an untuned car make sure your using 87 or like billybix said it could also have bad effects.