I am installing a hotcam kit, hooker longtube headers and few other small things on my car and ran into a really good deal on a mufflex 4inch system so I bought it too. Is the 4 inch going to hurt me since I have such a mild motor setup? I know I won't have to worry about a cutout anymore because there will be essentially no exhaust restriction. I do plan on installing N2O next and thats why I wanted a good flowing exhaust, but will it hurt my motor passes?

 

Your money would be better spent somewhere else. There are many people who have over 500rwhp with a 3" exhaust, so 4" exhaust is definitely not necessary for you. Would it hurt? Probably no, but I would find somewhere else to spend that money, like a dyno tune. Good luck.