Centrifugal blowers drive much different than Roots/Whipple positive-displacement pumps. Different from a turbo, too, even though the compressor design is the same thing. Down low, centrifugal blowers don't make much additional power, because they have to be designed so the compressor won't stall at max RPM and since boost is exponential this means they can't do much at the bottom of the RPM range. A Turbo, which is load dependent not engine RPM dependent, will make good boost at lower RPMs. And a Roots/Whipple is like a peristaltic pump, it moves the same volume of air per rotation regardless of rotation rate.
IMO don't do a centrifugal blower unless your only objective is WOT operation, or you will be disappointed.