Well, as is true with almost any automotive piece, when it comes to exhausts, you get what you pay for. First, your dad has to ask him self a few questions.
1) What is important, sound or performance, or a balance of both?
2) Do i want to change the muffler, the cat-back, the intermediate pipe (H-pipe/cats), or everything.
If sound is what he is after, then a simple muffler swap will do the trick. Flowmaster, Magnaflow and others make nice sounding systems. (Although the whole Mustang with Flowmasters thing has become almost cliche :rolleyes: )
If he wants sound and a little performance improvement, then a cat-back change could be the answer. Magnaflow, Borla, Bassani and FRPP (Ford Racing Performance Parts) make nice systems. They will alter the sound significantly along with some mild (5-10hp)performance gains. The new FR500 piece from FRPP is one of the best in terms of performance (showing gains of 12~14hp and tq on a stock 2001 Cobra) but also one of the most costly at $599.
If performance is his primary goal with sound secondary, then a change of the intermediate pipe and cats would be the road to try. Replacement of the stock H-pipe and its 4 cats with a free flowing X-pipe or H-pipe (with or without cats) will offer an good improvement in midrange and high end tq/hp. Usual gains show between 10~20hp depending on the car. As for sound,a tuned H-pipe will give more of the muscle car burble, while a good X will offer more of the high end scream. Dr. Gas, magnaflow, Bassani al offer good pipes with or wihout the cats. Be aware, that an off-road pipe (sans cats) will require the use of MIL eliminators to avoid the dreaded CEL (check engine light).
Now that being said, my personal recommendation (and what is going on my Cobra this fall) is the Bassani Catted X-pipe with the FR500 cat-back. THis offers excellent power gains (they compliment each other well) an the sound is amazing. its got a deep burble growl at idle, and screams like a pack of cyotes at WOT.
