I saw a Roush stage 3 supercharger for sale and I was wondering how these are? It says it just bolts in the place of the stock intake on top of the engine? I was wondering whether or not this would limit me on upgrading to PI eventually? Also im assuming this is a pretty tame supercharger since it probably came on factory Roush Mustangs. Im guessing I would probably only gain around 50-75hp corect? Also since it probably is a fairly tame supercharger what would I have to upgrade? Fuel injectors, fuel pump? I know I would probably need an sct tuner.