gears help big time with the stangs. at least if they have the factory 2.73 gears (i think that's right.) stepping up to 3.73 or even 4.10 will help a lot. there are many types of headers for it, he could also have an X or an H pipe, w/ or w/o cats. high flow mufflers and large diameter tubing. that thing will move. this is assuming it's a 5spd. if it's an auto he's talking out his ass. 13's can easily be achived with an auto 5.0, but will need a lot more work then just exhaust and gears.
