How much boost for 500whp?

Yo dog whats up on my b16 at 15 psi i was puttin down 407 when i cranked it up to 20 ish i know it was close to 500 if not right on the money or a lil more but my turbo manifold and down pipe is 4 sale good a set up that you want and i will sell it cheap for a manifold and downpipe thats ready for a eg and a tial 44mm vband wastegate