how much u booost gst turbo to how much.... can it go to 500 hp.

i have heard of stock internals taking up to 20psi if you have proper fuel managment and a upgraded turbo and ignition system..
as for 500hp i have seen a ddaily driven gs-x with 450@ wheels without nos. the 4g63-t is a very capable motor

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On C16, a stock 4G63 can hold up to 25-26 lbs of boost. On regular pump (Crappy 91 octain) I would not recomend going over 19-20. The motors can also handle 400+ hp's. Yet the transmission gets a little tricky above 350.