yea but you are still spinning the screw (or turbine or whatever)
the pulley isn't set up on a clutch (that I know of) so you still have parasitics.
it may not be compressing but it is still spinning. there may be a reduced load if there is no pressure being accumulated but the load is still there.
(load being drag on the belt thus HP required)
I was addressing the fact that the poster stated superchargers make boost dependent on RPM and not based on load, which is only true under 100% throttle conditions. At part throttle boost is load dependent on superchargers due to the bypass valve.
At part throttle boost is throttle and RPM dependent on superchargers due to the bypass valve.
Fixed that for ya.
I came across this in the wikipedia article on superchargers, under the aircraft section:
A supercharger has to take its drive power from the engine. Taking a single-stage single-speed supercharged engine, such as the Rolls Royce Merlin, for instance, the supercharger uses up about 150 horsepower (110 kW). Without a supercharger the engine would produce 750 hp (560 kW); with a supercharger the engine now produces 1,000 hp (750 kW), a total increase of 400 hp (750hp - 150 + 400), or a net gain of 250 hp (186 kW). This is where the principal disadvantage of a supercharger becomes apparent: The engine has to burn extra fuel to provide power to turn the supercharger. The increased charge density increases the engine's specific power and power to weight ratio, but also increases the engine's specific fuel consumption.
So in that case, the engine has a 1000 hp output with the fuel consumption of a 1150 hp engine. Yes, a clutch and bypass valve will help with that, but if you're not using the supercharger, why bother installing it?
A functioning supercharger will reduce the engine's efficiency (in terms of BSFC), and a fully bypassed supercharger isn't going to improve the efficiency of the engine as the engine will be operating just like a normally aspirated variant... The supercharger will only be dead weight.
And heavy. The bank of batteries needed to run the contraption for more than a few seconds at a time will load the car down. And then there's the energy loss from charging and discharging the batteries to consider. It might be more practical on a car that's already hauling that stuff around, like a hybrid.
I think a supercharger has it's place as long as you downsize the engine so it can run at a better BSFC, and only use the supercharger for those times when you need more power than the smaller engine is capable of producing.
That is also why I like the electric supercharger, since you only need to replenish the energy with the existing charging system and battery.
You would probably only use the supercharger less than 1 % of the time.
Well, I found out that GM patented my idea a while ago so it's no secret.
I have a venturi air mover that produces more CFM than I would need. It takes about 60 psi from a standard air line to produce something like 800 CFM.
I would use an air compressor (I was thinking a tiny 2 stroke engine). I think this would produce the least parasitic loss, and a tiny 2-stroke would barely use gas. I would connect the throttles, and make a cam on the 2-stroke throttle, so the engine would produce just enough to keep the air tank full.