Quote:
Originally Posted by SVTSHC
Well truthfully the best fuel mileage is produced when the car isn't boosting. Centrifugal blowers only make boost under load (I.E. during spirited driving, uphill climbs, trying to pass another car, flooring it for the sake of flooring it), so under normal driving conditions when you aren't being an animal with the throttle you'll get the same fuel mileage you did when your vehicle was NA.
So essentially the rules with a centrifugal blower are the same as without one when you're boosting (or in an NA vehicle, driving WOT or almost WOT) your vehicle compensates with additional fuel; with a centrifugal blower that's when you take the hit.
The only reason people typically claim they've lost fuel mileage is because... well.. who supercharges a car without "spirited" driving in mind lol.
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Replace centrifugal with Roots and it's actually the story, because they all come with bypass valves. Electrically activated clutch would be slightly better, and clutched twin screw compressors would also suffer no parasitic loss. Twin screw Lysholm compressors will consume a small amount of energy when being spun with no load though.
The difference is under load, a centrifugal supercharger has slightly better efficiency.