OMG....OK the screw on top adjust the BOV. There are two springs in there that sit under a large washer that, when you tighten the screw, smashes the springs making it harder for the valve to open and vent the extra pressure. As far as the amount of boost, I've heard of people running 25psi on the Greddy Type-S...I wouldn't push it much more than that though.

And what vacuum line are you talking about, I have a Greddy and you hook the intake line up to the top nipple and that's it. What are you talking about????