Personally, i would not buy the p5 sport exhaust, simply because of the price. I found a much better one for a cheaper price than the one you can get from the dealer. I bought a Virant one for 250 Canadian and it looks much better ( in my opinion) as well as it has been through a dyno test... it "reports" an increase in 9whp, but realistically i just bough it cause it looks nice and has a nice low rumble... my car doesnt sound like a 4 cyln.
Anyways, yes it will add Hp, cimply because most of the presure is relaesed when yo buy a new muffler, but i dont htink it will be 10-15 like some people say. If i am not mistaken, there is a user on here that posted a dyno chart with the sport exhasut, and did get some hp out of it. Also, dont be fooled by tinking a catback will give you twice as much... yes, they will most likely give you an extra 1 or 2 hp, but they are not that much better than an axle back exhaust if you look at the price. But then again, to each his ow.... but dont get me wrong.. i would rather have a full stainless steel exhaust including headers and all, rather than just a bolt on axle back that i have.... but for 250 Canadian, i cant go wrong, and i have no regrets at all with the Vibrant... i will post pictures as soon as i can.