I just bought a supercharge for my ls vtec setup. Ls block with gsr head. I needed to know what size belts do I need? Please help me out. Should I go with 3 or 2.5 exhaust.

 

Belts, consult the supercharger manufacturer. They should have that sort of thing figured out during R&D.

And exhaust, depends what power level you're making. 2.5 should do though. Exhaust size is more of an issue on turbo because it relies on a pressure differential to make the turbine spin. NA or supercharger, you have a header and that along with the rest of the exhaust system works as a whole to actually suck exhaust gases out. The pulses help draw out exhaust from the next cylinder that fires. This is why you see different size and differently shaped headers.