Big-Bird wrote:Leave the Catalytic convertor(s) in place because it's the right thing to do there
I agree but if you really want to go performance there are high flow cats available. My brother has used them before with a somewhat noticeable sound and "butt dyno" difference.
I've heard headers do very well on the 4.0. Nissan sells the best ones of these that I have seeen (Nismo). A Cold air intake often will change the sound of your engine a bit (not really the sound of the exhaust, but the sound you hear in the cab). NIssan offers a good one, as do other companys. I believe the F5 fuji (i think that is right) is on a thread in this forum and has produced good results on the dyno.