How to figure boost from hup and blower pully size? Whats your psi and belt size?

Also how do I figure out what size belt other combos would produce? I'm trying to get away from the 42inch belt to either a 41 or a 43 so I'm going to need to change one of the two pullies. Right now from the outside I have 4 1/4 blower and an 8 inch hub.


ATI D-1 Setup