X pipe?

ahh.....i am really stuck here this might be a dumb question buy the x and h pipe are exhaust parts right? and how would i put one on if my flowmasters it welded on....??? and how many hp does it add?
thanks
 
Ohhh, don't get me wrong. The Mac stuff always sounded great, but the Fox stuff never fit right, had thin, prone to warpage flanges and rusted almost the second you took them out of the box. Although they performed and sounded great, they were an inexpensive product for a reason.