Just to add to Mr Pockets answer.
The centrifugal type blowers, either belt or turbine driven, were designed for constant speed engines, about 2000 rpm variation max.
Truck or plant diesel engines, aircraft or boat engines, that run at a constant engine speed. They are most effective in this role, but are out of there range if the engine speed varies too much, as an auto does. They can pump more pressure than a positive displacement blower, but at a higher RPMs.
The positive displacement blower, such as Roots and the screw type, are more suited to the wide speed range of the auto engine, that can be as much as 5000 rpm. This type can pump to about 14 psi, not as much as the centrifugal but it can do from idle, right through to peak RPMs.
When used on a auto engine the PD type will produce a wide flat torque curve. The centrifugal, will produce a peakier torque curve, that is more to the top end of the rpm range. This usually needs more gears to spread the torque across the operational range.
Harvey.
