As many of the guys who have played with turbos know, when you port and polish your head, you will actually decrease boost, but, you will not decrease power, you are simply making it easier for the turbo to do its job by giving a smoother path in/out of the cylinder. polishing also helps keep the fuel charge dense, as it does not get "smacked" around and broken up by the rough castings, and it makes it harder for the charge to pick up heat from the head, and also helps exhaust heat not soak into the head.
