I was wondering how much hp i would gain, if any, from adding a full catback system. I already have a CAI installed

 

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Here is an idea and not a flame. Why not goto http://www.dynojet.com/lauto.shtml and find the nearest one to you. That way you can do a baseline dyno with your intake then dyno again after the catback. We don't have enough dyno's to really know how good/bad a catback is. Truth is you might get 2-4hp in the midrange or toppend but you could just as easily lose 1-3hp in the lowend. I would say get a Y pipe first before exhaust, both are around the same price but you get way more gains.