Twincharging an engine that features a screw-type supercharger (ie it already has internal compression) in my mind has the following advantages and disadvantages:

Disadvantages:
It would still feature parasitic loss when the supercharger is "bypassed" and the turbo is powering away at higher rpm

Advantage:
The efficiency being better than a roots blower, would mean lower temps and more power

Can one of the gurus post their thoughts? PatPrimmer and Warpspeed had a lot to say on previous TwinCharge topics.

In short: what is the suitability of screw-type SC for twincharging project?

You've probably got it ... the screw type would give (theoretically) an efficiency loss during cruise, but a minor power improvement during the short period of acceleration until the turbo takes over.

The twin-charging application that I'm aware of (VW) only uses the supercharging for the first moment of acceleration in which the turbo is running "off design". As soon as the engine builds enough revs for the turbo to take over, it does. This leads me to suspect that there is little purpose in using a higher efficiency supercharger, because it is really only used for maybe a second at a time. Also, those engines are intercooled, so whatever minor extra heat comes from using a supercharger that is less efficient than it could be, gets taken away by the intercooler anyway.

At least in that application, the need to minimize parasitic losses during cruise and acceleration when the turbo is active takes priority.

'course, not every application is the same, I'm speaking only of that one, where VW's intention was to make a downsized and more-efficient gasoline engine; it's best not to throw away a few points of efficiency driving an inactive supercharger.

FWD in what body? An imprezza or liberty, or something entirely different?

Here's some pics:






Alternator, Power Steering Pump, AirCon Compressor - which one are you going to remove? Or, will you accomodate them with a bracket to re-mount it a little to the side?

This is getting off-topic, so this will be my last post on the subject (a valid e-mail address will not be hard to find if you wish to go off-board) but the models here are a tad different, and all one needs to do is look into "reversed intake manifolds" (positions throttle to face forward) to see the options for relocating accessories.

Trying to steer back on topic, the screw type superchargers require less power for a given boost level, so the drop in parasitic loss alone would be advantageous. 

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