Don't go beyond 6 #'s of boost without upgrading the internals. You will blow the engine. Bob Stockum is the turbo king for the PT.
http://www.bstockum.com/
He deals mostly with the Hahn turbo but is an ASE certified mech and is a guru with turbocharging the PT. He can also tell you what you need to do if you want to raise the boost.