Ok. So my crank pulley is 127mm o.d. which drives a supercharger pulley 73.27 mm o.d. to make 9 psi of boost. The problem is, the supercharger puller is too small and causes the belt to rub. So i increased the supercharger pulley to 101.6 mm o.d. and now the it only makes 4.5 psi of boost (not enough) I have someone who is going to custom make a new crank pulley, larger than the current one to compensate and make 9psi of boost, by keeping the 101.6 mm o.d. supercharger pulley The question is, what size (o.d.) does the new crank pulley need to be, to drive the 101.6 mm o.d. supercharger pulley to make 9 psi of boost? I took an engineering class 10 years ago and used my distant memory of gear train ratio calculations. But i got two different answers, 160.2 mm o.d. and 175.77 mm o.d. This of course made me second guess my calculations and it didn't help that my boy called me an idiot for even using the this formula: Since- 127 : 73.27 = 9 psi [127/73.27 = 1.73] or 57.71% Ratio- 1.73 : 1 = 9 psi Therefore- 1.73 x 101.6 = 175.77 mm o.d. Please advise, thx.