Hey, if you're interested in what is required for a supercharger build, this post lists it all for stage I and stage II.
http://forum.liberty.asn.au/viewtopic.php?f=15&t=18923
As Hyrax said: stage I brings a 2.5i up to WRX power with stage II pushing STi power. Many will say just get a GT and they have a very valid point. As others have shown, there is so much work involved with putting a turbo on an NA car, and you will need a VERY good mechanic that is willing. However I enjoyed experimenting with my car, I learnt so much and I'm certainly enjoying +185 atw Kw