is a s/c always in boost? in a turbo if your half on the throttle at 3k rpm your not as much boost as wot at 3k rpm but a supercharger runs by engine speed so if i were using a 9psi pulley and cruising at 3k then would i be at 3psi even at 10% throttle???

 

yeah, that's pretty much how it works for centrifugal superchargers. centrifugals are belt driven, so the compressor produces boost pressures that are roughly in direct proportion to RPM. so if 9k = 12psi, 6k=~8psi, 3k=~4psi etc.

it's different for roots superchargers (ie SOT), which are always around full boost.

 

Only if you open the throttel.


In a roots the TB goes before the Supercharger this throttles the supercharger.

Having the TB before and the internal by pass on the Eaton MP series of superchargers reduces the drag on the motor when not in boost therefore there is minimal effect on your MPG.

 

cool, thanks for the clarification!

 

so highway cruising with a centrifugal will give me crap mileage and increased wear?

 

Not sure if they all are set up the same way, but the BOV on my Vortech is open and venting boost under both cruising and deceleration.

 

vettes2k

has it correct


on a VT CT or KW setup ether is internal compression being done on the incomming air even when at low throttel angles so there will be a bit of positive pressure coming out of the compressor. This is where the bypass valve on a CT/VT/KW comes into play.


The bypass valve opens to release this pressure ( more correctly called head pressure) this effectively drops the amount of work ( AKA drag on the crank) on the compressor to just the work that is being done due to internal compression.


Just like the CT/VT/KW units a roots style also creates drag on the crank at low throttel angles but do to a different reason then work still being performed on teh incomming air charger.

How the roots gets around this ( one way) is by placing the TB on the inlet to the Supercharger. By not allowing a lot of CFM to enter the supercharger when at low throttel angles this reduces part of the drag on the crank. No air to do work on so it drags the crank less.

The other thing a roots does is it has a bypass valve the opens in vacuum ( smiler to how the CT/VT/KW work) with a major difference.

Since the TB is pre blower this bypass valve opens up the area post blower to blower inlet after the TB. What this does is equalize the pressure ratio between the inlet and outlet of the Roots blower. So the blower is not pushing a lot of air through its rotors instead the air necessary to keep the motor running is coming through the bypass valve.

So the only drag modern roots superchargers have ont eh crank when at low throttel angles is due to the energy to just keep the rotors moving and the internal frictions in side the supercharger.


End the end a KW/CT/VT supercharger Vs a roots supercharger have about the same drag on the motor when just cruising around at constant throttel.

 

how much power are u making?

 

thanks mugenrios2k. i had to read it a couple of times but good info!

 

No peristaltic drag noticed, or reflected in gas mileage. If anything I have noticed an improvement in partial throttle response, which I attribute to the air movement created by the blower being consumed by the engine under no boost pressure. Also by the time any drag is created by the blower, the boost pressure it creates begins to offset this. So in other words when comparing stock to centrifugal blower, there is no portion of the throttle position/rpm where the blower is creating perceivable drag on the motor making feel sluggish compared to stock, the blower is beneficial in all conditions.