If you increase the valve pressure (turn in the screw), you increase the valve's resistance to opening at lower vacuum levels, meaning part throttle or at idle but you also increase the occurrence of compressor surge, which is what a BOV is there to prevent in the first place.
Skyline R34 GT-T and Silvia S-15 Spec-R has the same price (for year 2000). Why is Silvia so expensive? Skyline is 2.5 turbo compared with silvia's 2.0 turbo. performance wise which one is better?