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st184 sillycar
Forums Junkie

Location:
Melbourne
Registered:
June 2004

Re: i need a supercharger

Sun, 22 August 2004 08:10

rozz wrote on Fri, 20 August 2004 18:56

how does a Centrifugal S/C work
i just wanted a posivtive displacement instead of a suck through type charger, as in a s/c before the inlet madifold instead of after

You mean before the throttle butterfly, yeah?

Yeah - the majority of screw/roots positive displacement S/C's are designed to bolt in between the throttle butterfly and the intake manifold. Don't know if I've seen a centrifugal S/C mounted behind the throttle butterfly. I assume the pumping losses at highway-cruise would hurt fuel economy too much. I don't think one type would be significantly easier to install/setup than the other.

Like Norbie said, a positive displacement S/C will pump a fixed volume of air for every revolution of the crank, regardless of revs. They tail off in efficiency as they get towards the top of their intended rpm range. This tends to give stump-pulling torque at low rpm, with linear performance until the engine and S/C lose efficiency past 4->5,000rpm.

A centrifugal S/C is sometimes called a "belt driven turbo" because it runs a similar compressor wheel + snail housing. No exhaust turbine driving the compressor. These have little effect below 2,000rpm, and build boost as the square of engine rpm, until the compressor maxes out its flow-rate. Similar response to a turbo engine, but without the lag, and without the "turbo rush" when turbo motors suddenly start making boost. Centrifugal S/C's ramp-up the boost much more smoothly though, more of a "swooosh" when coming onto boost, instead of a turbo "thump."

I think the easiest way to do install either type would be to go:
Air filter -> S/C -> B.O.V. -> AirFlowMeter -> ThrottleBody -> Intake manifold.

That way, you don't have to mess with the factory throttle body, and if you've got an air flow meter you don't have to worry about the BOV plumbing. Because supercharging gives the same psi of boost per-rpm every time, you should get away with minimal computer changes. A piggyback cpu should do it, unless your factory ecu is re-programmable. (in theory)

There's as many ways to force air into an engine as there are to skin a cat!! Hope this at least gives you something to think about!!

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