15kw taking AC out?? hmm ok.
dont worry about the Forward facing plenum until you get close to 300kw. stock flows great up until then.
a good option would be a highflow 25 turbo, uses same exhuast, lines, manifold, everything.
then get a piggyback ecu (or a stand alone if you want) and get it all tuned. see if your happy with how it feels and go from there.
CJ
o and if the wastegate isnt closeing properly, try slightly bending the arm, its not a FIX its just a bandaid. or just stay off full boost