Please don't overlook the source of energy used to drive to electric motor. Let's "guestimate" that a 20HP motor will be adequate to turn a Roots or belt driven centrifugal compressor supplying 4lbs of boost at 600CFM.

1HP is equal to 750 watts (ignoring conversion losses), so a 20HP motor will require around 15kW of power. With a 12V battery that would be around 1200 Amps. With most alternators capable of sourcing only 65-150 Amps the batteries (2 each minimum to support the 1200 Amp demand) would be drained within a couple of minutes.

The approach is technically feasible, I just can't see it being at all practical.

Cheers, Mark