IPD says 6hp. Based on my experience with my own 2.25" exhaust which I built myself, I'd say that's close if not slightly conservative. Its a very noticeable gain, especially in the high end. The throttle body better be done right or it'll just make driveability crappy. If you're planning on more mods, then the throttle body may be for you, but if that's the end of it, it's probably not worth it. I wouldn't be able to give a hp figure. I say get a cam and screw around with your airbox. Exhaust, cam, and intake mods should be around 20 extra hp depending upon how wild the cam is. Good luck with the project.