I have another hair brained idea. Want to make a squirrel cage blower on the really cheap. I have a motor, variable speed and its controller. Need to design a cage that will pull 400 cfm. How do I figure the size of the cage, and the casing for it. It will suck out a volume in a 18" x 36" x 22" deep with a maximum of four feet of 4" dia. vent duct work. My motor is 1 H.P. VDC. It will be for a hobby airbrush spray booth type application. Any help will be greatly appreciated.