twin screw blowers based on the lysholm design are best. The boost is there the second you touch the gas. they are the most efficient and do not add too much parasitc drag. Whipple and Kenne Belle are two manufacturers making twin screw blowers. Unfortunatlely, they do not make kits for a 351w. I corresponded with Kenne Bell on the matter and found you could fit a whipple to a 351w if you had EFI and the right lower intake manifold. I am informed that a correct intake would come off an F150 Lightning.
Roots blowers give you instant on boost but they are terribly inefficient and die out at higher rpms/speeds.
Centrifugal blowers function and perform a lot like a turbocharger only they use a belt to spin the impeller and not exhaust gases. you might see some lag but when it kicks in it keeps on going. These are very efficient and do not create the kind of parasitic drag a roots blower does. Paxton makes a centrifugal blower for a carbed 351w. If you have an auto and are worried about the turbo-esque lag, you could compensate with an appropriate stall converter. I think the boost comes on like around 2500-3000 depending on the blower. With a 3000 stall converter, you would be right on the money.
