Originally posted by tan

That is a case comparing superchargers: Roots Type (aka Eaton aka Positive Displacement) versus Centrifugal (a turbo is also considered to be an exhaust driven centrifugal s/c). Centrifugal type, in order to be efficient, they must be spin at higher velocities than the engine crank (thus for superchargers, a geartrain is needed to multiply the crank speeds). This is why OEM and a certain tuners (Neuspeed & TRD) uses a Roots Type supercharger, less complex.
Nah, the reason why they use roots is because they provide torque faster than centrifugal type S/Cs. Roots typically run lower psi, but spool up faster and proved full torque at lower rpms. Centrifugal SCs are for peak hp and top end.

The arguement about displacement is valid. Top fuel dragsters are still the fastest cars at the track and you never see any running small displacement. But, on the same note hp/weight is very important as is gearing. A many a car now a days post high hp numbers, but are heavy and geared bad for fast 0-60 and 1/4 times.