Ok, on a completely stock 2003 WRX, if I were to add a manual boost controller to it, would it be safe to go above 15.5psi for DAILY DRIVING. I was under the impression that 15.5 psi was as high as you could go if you wanted the car for a daily driver that would last a while.

(P.S. That extra 2 psi of boost would add how much horsepower?)

 

15.5 PSI is the most boost the factory turbo can make while staying in its efficency range - go higher than this an your turbo will wear out quick and you will be introducing a lot of unnecessary heat to your motor. If you want to run on the edge of the turbo's efficency I would buy a good EBC unit rather than a MBC to prevent problems with atmospheric pressure changes. Or get a UTEC, get the same kind of control and be able to advance your timing and add fuel. You would get 35HP or so from that setup, not sure how much with just a EBC/MBC.