I have an '03 GT, and have been considering putting headers on it. How much of a difference on average does this make as far as power increase? Also, what kind would you suggest? Sorry if there have been 1000 questions like this already. Thanks

 

Well headers going to the factory H pipe isnt going to do the car any justice at all. You need to get a good off road X pipe and a set of magnaflows to throw on that puppy and you will be looking at about 25 to 35 HP gain. Exhaust and intake is always the first things you need to invest in.

 

get long tube headers. dont settle for mids or shorties.

 

For real. Shorties are the biggest waste ever on a 4.6 - I saw a dyno article on a 4.6 2v car that got 3 hp from a shortie header swap a while back. Im suprised they even got that much. Go long tube or nothing.