While the roots blower is inefficient with a big power demand on turning the rotors, they are well proven torque makers and monsters. The roots will pound out power (torque) on demand from idle to redline.
The centrifical (sp?) units build boost. In other words, you wait for it. This makes them more street friendly. They also push the torque curve and peak upwards. More boost equals a further push of the peaks in power and torque.
