Quote:
Originally Posted by whats77inaname
Roots type vs centrifugal.
I.E., the s/c'er is contained inside the manifold as opposed to being a separate unit that sits outside the manifold.
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More accurately its a twin screw, vs centrifugal. It's not a traditional straight lobed roots blower.
All kits except the Harrop kit use a centrifugal blower. This is essentially is the compressor side a turbo, but instead of being powered by an exhaust turbine, its powered by a pulley connected to the engine.
The harrop is a twin screw positive displacement supercharger.
A centrifugal blower usually takes more rpm to make boost than a twin screw or roots blower. However, they provide very good upper rpm performance.
A roots blower makes very good bottom end power, but usally tapers off in the upper rev range.
A twin screw blower on the other hand behaves like a roots blower only better in every way. It gives good bottom end like a roots blower, but gives power better than a roots blower in the upper rev range. Its a largely more efficient design, which translates into more power. Twin screw blowers are more expensive to manufacturer than a roots blower, which is why most cheap kits you see are roots blowers.
The harrop kit from everything I have seen appears to be the real deal. A legitimate intercooled twin screw blower. Its adds power where our car lacks, in the bottom rpm range, and continues do deliver power in the upper rpm range.
I'd take a twin screw blower over a centrifugal blower any day of the week and twice on Sunday.