Port and Polish head w/ portmatched intake manifold, but you'll need injectors and header.

Gut your cat, chop the muffler off, put on a universal free flowing one, that's about $80 right there. Now, used header from eBay for about $100. Now you're ready for nitrous if you want, but I think it's kind of a waste of time and money (only get to go faster for a quick burst, and it's pretty bad on your engine).

Now you have about $600 there. If you want some quick performance, something that wil last for the long run, get this: http://cgi.ebay.com/ebaymotors/ws/eB...tem=2429162023

That's for an LS, but maybe they'll do one for a GSR, not too sure, e-mail them. If they can, for $600, that's going to be your BEST hp/dollar. I'm going to do it.