Bigger crank pulley = more boost. Smaller blower pulley = more boost. You run your boost gauge to a vacuum port after the blower. It is possible to over spin a blower be it a roots or centrifugal. The hot ticket is to get the largest crank pulley as possible, and size the blower pulley to suite your boost.
Oh I see, well I'm running a 5.0 crank pulley which is 6 inches and both of the roots style superchargers have 4 inch pulleys right now. Is there a way to calculate the psi or do I just have to hook it up and read the intake vacuum pressure after the fact?