what kind of fuel you use?

100 Octane Racing Baby...

93 shell. everything else around here is water.

Fuel from station to station is different. Remember that all the fuel is literally the same, it's piped to a local hub where the trucks fill up to take it to the fuel stations. They don't keep track of which refinery the fuel came from, the only difference is the additive package they add which makes a minor difference.

You should try to use a fuel station that is fairly busy so that you know it's fresh fuel, fuel even just a few weeks old can hurt performance. And, of course, a major brand name tends to have the best additives. I like to go to the newer clean stations that get a good amount of traffic.

When I lived in Oklahoma there were a few stations that had 5 different grades to choose from, 87, 89, 90, 91, 93. No idea why...
Dan

No name brand 87 octane that contains up to 10 % ethanol on my stock GT. Seems to do fine, but I wonder if any of you have issues with tunes and gas that contains a small amount of ethanol?

believe it or not / it makes a difference

From what I heard even the 99-04 cobras dont need the premium. It does say they take it but one of the meeting I went to as mechanic we were told no car HAS to take 93 octane. It does make it run better especially if it says to use it I would but in a regualr GT I wouldnt worry about it. It may give it 1 horsepower or something but nothing to make a difference and you probably wont even feel a difference in the performance or drive

From what I've heard (someone correct me if I'm wrong), but 87 octane burns quicker than 89 or 91 (California guy). Engines with high compression ratio's, high rev limits, and supercharged/turbos need the 91+ because it takes longer to burn. 4.6 3v can technically run on junk as low as 83. Just avoid getting gas when a tanker is filling the tanks because it rustles up the junk that nomally settles to the bottom.

Vat you are somewhat right. The higher octane fuels are harder to ignite, so are less likely to preignite in a higher compression engine, that is why high compression engines need it, but the lower octane fuel actually has a higher energy content. That is why a car that does not need higher octane can actually make LESS power and get worse gas milage if you put 93 in it.

21mclcar, that is wrong. Engines with higher compression do need higher octane fuell. WIthout it, they will ping and could be damaged. Modern cars though mostly have knock retard that is advanced enough that if you put the wrong fuel in it can correct the timing enough to prevent preignition, while loosing power. Some cars actually say to use whateer you want and it will just make more power on higher octanes, like cars with the supercharged GM 3800, the comuter just adjusts timing and fuel trims to prevent preignition on lower octanes.

That being said, the 05+ Mustang GT 4.6 has such low compression it would practically run on water. If it's stock, I'd use 87 and nothing more. My car is tuned for 93, so I use 93 from whatever name-brand gas station is convieniently located (usually BP).