I have a 4.5 Whipple on a 572 ci in engine . The mechanic put a 9 inch pulley on the crank and a 4.25 on the Whipple. I'm at 6 lbs of boost at 3000 and 12 lbs at 4000 .......This is crazy ! Does anyone have this set up and what size pulleys are you using ???

Your driving it off a 9" lower pulley?

Yes , The mechanics set it up and its way, way wrong... Had a 3.3 on it and now a 4,5 . Pulley advice ???

You have to get the spec on air moved per rotation of blower. Worked in with compression ratio of motor. I think you are going to end up closer to a 1:1 ratio on pulley sizes. I would not want a 9" on the blower. But getting the crank pulley down around 4 to 4.5

That is about 110% overdriven