yet another one... unlike most DSM's and some Nissans, you really cant just turn the boost up and get performance increases on a stock car....
things go boom real fast
to start, the main one...
_THE_ WRX Modification Guide *Complete*
and some more:
Bluedemon has some nice things to say in this one...
04 Wrx Boost ?
boost controllers
max. psi on a stock wrx