Got Boost ???

There are several references on supercharger design and all contain various formulae and discussions on the superchargers and related design criteria....read'em, done that.
Of particular interest is your individual application (engine size and type, supercharger size and type, and intended use) in order to correctly determine the speed (flow/boost) of the unit. The MagnaCharger is a roots design and boost is closely related to RPM. A number of variables come in to play and all must be considered regardless of the formulae.

I sized the drive components according to the references for the 90 cubic inch 4th generation MP90 by Magnuson at a pulley diameter of 4.1" for 1.5 lb. of boost. The calculations did not factor in the volumetric efficiency of the MP90 (.74) in the 6000 rpm range and the calculated and measured boost at .74%  is actually 0.0 lbs.
Changed the supercharger pulley to 3.8 in. from 4.1 in. (1.513 pulley ratio) and observed an increased boost to 1.0 lb. This is fine for a street vehicle used only for crusin'.

At my age, it's not the launch from the stoplight that's important........
It's how cool you THINK you look when the light turns green!!

 Now the supercharger is turning
almost as fast as the fan blade which is
turning way too fast..... 6352 rpm at 4000 rpm engine speed. Imagine a Star Wars light saber, thats my fan.
The answer is on its way to Dicks Tool and Die shop for slight machining (new fan pulley) and will post the results as soon as I get it installed.

This is the new 3.8" pulley, I found a 3.4" pulley on Ebay last night..... 
2.9 lbs. of boost. I'm thinking .........