Andy put it very clearly. One other thing I would point out from my experience since some of the earlier posts were inquiring about changing the blower but not so much heads or cam...
When I first started on my upgrades, I wanted to stay external on the engine. I planned blower porting, throttle body, CAI, pulleys, exhaust, heat exchanger, all "external stuff". Well once I got that blower off to ship it out for porting, there staring me in the face was a regular old LS engine stripped to the point of making a cam/head swap not much additional work. My project quickly turned into a full 700rwhp build.
My point is if you want to stay external on the engine, don't touch the blower! Most of us gear heads, I imagine, will suffer the same fate as me if you do. It's just too easy to swap a cam and heads!
You'll love the new power though!
