GT99GT

I was wondering what the difference is when filling up the mustang. I have a 99 GT and it says in the manual to fill up with 87. I purchased the car used and it has 57K miles now, im not sure what fuel the previous owner used to fill up but i fill up with 91. Is it bad if the person before me didnt use 91 and i all of a sudden start to use it. Also is it bad to use 91 if it says use 87 in the manual. im sure it says use 87 for a reason, im not exactly sure of the reason though. another thing, i heard from one of my friends that has a mustang that you should rev your engine before turning the car off because it cleans piping or something of that nature. is that true. just a slight tap to rev is to about 2k rpm and turn it off. Im not sure, doesnt sound like it really does anything but i might as well ask, u never know. thanks

jeep45238

The octane rating is only what the engine was desinged to run on. The minimum rating is to fight off detonation. It won't hurt to use higher octane rating, but at stock levels, it's a waste of money.

vfast

just throw in some mid-grade and pocket the saving...now is the time to bump up your timing.
reving before turning off engine doesn't help anything

N2OJunkie

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I have to go up from 87 to 93 after installing a nitrous kit.</P>

hotrodman

i have a cobra a aways but 93 in it if you can buy a mutsang it should get the best gas dont you think@!!!!!!!

Daytomann

I have heard not to go over about 89 with a stock GT motor. Plus once you go up for a long period, do not go back down.</P><edited><editID>Daytomann</editID><editDate>37992.4765393519</editDate></edited>

yellow4.6

I use 87 with no knock on stock motor. Why spend the extra money on the gas if you don't need to. The z28 LS1 was supposed to run on 87 but I had to use 91 or better orI would get engine knock at higher rpms. The new 300 hp 3v will also run on 87. I love Ford!!!

redfire GT

The stock GT motor was designed to run on 87 and if you go higher, you will lose hp.

vfast

you wouldn't lose hp going to 89... any kind of induction 93 is why I used 93 plus 1 can of nos octange boost for my s/c

N2OJunkie

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But if you add some juice then you need to go higher.</P>