The H or X pipe helps reduce some of the popping sound when coming down on compression. If you have an auto it won't make much difference then.

 

auto bahahahah me no 5spd all the way check the sig but i think im gonna stick with divorced then i liek the whole poppy sound when i down shift and what not hmmm in fact i love it my jeep did it gah oh well damned telephone ploes i like my stang better anyway unh hun but yea what about the placement of the exits sraight out the back hidden or out the side rear bumper hidden?