i've got a '99 GT and my mom's been using it and she's been putting 93octane premium in it. as far as i know from the factory they ran on 87 octane and the 93 may be burning un-evenly.

what octane should i run in it, i live in FL so reg-87, plus-89, premium-93

the mods are-CAI, O/R X-pipe, cat-back, and 80mm MAF

 

I had a 99 GT with a off/road X-pipe and CAI and i used 87 octane.

You really are wasting money on 93 octane unless you get the computer retuned or you get a timing adjuster.

 

ok cool, did yours run fine and all. did you lose any gas milage or anything?

 

I don't really know if it lost mpg since i didn't do any type of comparison... but with 87 it did 27mpg on the hwy...

 

Go with 87. No need to burn money on 93 till you put a chip in it.