The stock block can handle PLENTY!
Just do yourself a single bolt-on and start getting speeding tickets galore and becoming good friends with Tire Rack!
Tom Byrne sells a VERY nice blower package for your car and you will be EXTREMELY happy with a 500HP package!
(hopefully Tom doesnt get mad at me promoting his business but he has the BEST picture of this package I have ever seen!)
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2004 GTO Magnuson Intercooled supercharger - Silver stardust finish $5989.99
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2004 GTO Magnuson Intercooled supercharger - Polished finish $6989.99
If you want more, Lingenfelter has a LS2 that generates 1038 REAR WHEEL horsepower !!! Downside is it cost $53,000.