what kind of cam are you running. the vac. on you blower motor should be the same as on any motor. i ran 6-71 blowers and power brakes with 16 in. of vac. should not need a cam that big for a blower. you can do what you want on the jets, but i cant believe holly is telling you to down jet a blown motor with a 750 carb. stock jets. the first blower i had was a 4-71, 6 lb. boost, blower cam, 7 1/2 to 1 comp. 750 holly 72 jets in the front and like 80 in the rear. trying to drive it on the st and drag race it i burnt holes in pistons or blew head gaskets 20 times before i got it right. right was 90 jets in the front and no jets in the rear. i started off doing what somebody that was suppose to know told me.