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toolman said:
Ive seen some stuff on Twin screw blowers and dont really know much about them. I was wondering what the real difference between the two are. Dont they both use twin impellers?
Roots blowers have straight-cut impellers -- while twin-screws have interlacing helix impellers. The twin screws are a lot smoother under acceleration -- while roots blowers tend to make a thumping noise as the amount of boost fluctuates.

Here's a nice article discussing blower basics: http://chevyhiperformance.com/techarticles/49378/
 

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big_mike said:
BUT, both are twin screw compressors and both rely on gearing to produce their boost.
I hear ya -- but the difference in impeller design results in a different classification in my mind. With the twin screw, the air delivery is smoother and much cooler. Don't have the time to follow it -- but I think the NHRA banned twin screws in the alcohol classes for a while because they made for such a difference in performance -- and that ban was specifically for the impeller design.
 

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Steve A said:
A "Roots" is an air blower and compresses in the manifold, twin screw compresses the air in the blower itself. Twin Screw is much more efficient and heats the compressed air less.
exactamundo...
totally different design even though they look similiar..
and ALL superchargers rely on gearing even centrifugals...
 

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The difference between the way the car will feel with a turbo vs a roots/twin-screw will be noticeable. I've had both and as far as low-end torque goes, you should go with the positive displacement superchargers (roots or twin-screw). If you're going to be spending a lot of time at high RPM, then a turbo is a much better idea. For street-driven cars, I have personally always preferred the PD superchargers. Of course you're going to get as many different opinions as there are types/brands of forced induction...each have their own merit.
The best way to find out which suits you is to drive a car as similar to your own as possible with the different types of forced induction.
 
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