My Engine was street ported by Peter Farrell Supercars.  Street porting involves enlarging the intake and exhaust ports which in turn  allows your engine to breathe better producing increased HP at higher RPM's.  Low end torque suffers a bit but but once the engine is revved it's well worth it.  The idle is also a bit lumpy, too.  I like the lumpy sound, however.  It resembles the lope of my old V-8.  It makes the car sound aggressive.  My ECU wasn't necessarily mapped for the street port, but the air fuel levels still look pretty good.  The street port worked really well along with all of my other modifications.  The more modifications you add to help the car breathe better, the more the porting is utilized to it's maximum potential.  After the porting was complete, the car was noticeably stronger and pulled significantly harder under acceleration.  I wish I had a g-tech to monitor the performance gain, but the street port felt stronger at 10psi than the stock port felt at 12psi.

 Approximate Performance Gains:     

Street port - 30 HP