Originally Posted by Forced370GTO

{[(crank pully diameter) / (Blower pulley diameter)] x (blower step up ratio) x (engine rpm)} / (max blower speed)... multiply that number by the max rated cfm of the blower. Store that number on paper or in your calculator... then take your discplacement in cubic inches and multiply by the same rpm used in the first equation... divide by 1728 to convert to cubic feet... divide by 2 to account for the 2 revolutions per 1 combustion cycle... now divide the first number you stored by this number... multiply this number by 14.7... this will give you your absolute pressure... then subtract 14.7... this will give you your boost pressure at the rpm you specified.

example for d1sc with 7" crank pully at 6000rpm and 370 ci of displacement...

{[(7/3.55)(4.10)(6000)] / 62000rpm} x 1400cfm = 1095.32cfm

[(370ci x 6000rpm)/ 1728] / 2 = 648.36cfm

1095.32 / 648.36 = 1.705 bar

1.705 x 14.7 = 25.066 psi absolute

25.066 - 14.7 = 10.366 psi boost at 6000 rpm

if your crank pully is a different size or your blower is different just plug in the relevant numbers and rework the equation... goodluck