well it will be alot, simply because you are getting headers... the hp difference won't be much with just the h pipe alone, the headers is where you will gain up to about 30hp. They can be on the expensive side depending, and from what i hear, a REAL pain to put in, almost pulling the entire motor to put them on. if you just swap your pipe, it will give you a little, but its still catted, so you won't see that much, just better sound more than anything.
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