Screw charger vs. Roots

Discussion in 'PSI Superchargers Tech Questions' started by Money Shot, Sep 14, 2009.

  1. Money Shot

    Money Shot Member

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    I am thinking about buying a screw blower for next season. What are the main tuning differences for a screw vs. a roots? Also, How much power can I expect to pick up by simply switching to a screw? Currently running a 14/71 SSI HH @ 20% over. BBC 565 Big Chiefs BAU Injector.
     
    #1
    Money Shot, Sep 14, 2009
  2. Mike Canter

    Mike Canter Top Dragster
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    If you are only running 20% over now then I would have to ask the question why you want a screw blower? A good screw blower can put out 55-60 lbs of boost at 10,000 motor rpm. How much boost do you make now? Also it is a totally different fuel setup. Why don't you crank up your blower and make some power now?.
     
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    Mike Canter, Sep 14, 2009
  3. Don Onimus

    Don Onimus New Member

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    Screw blower

    Unless you have around $12000.00 for a used set-up you don't know what to do with, Listen to Mike and others. Also will that motor stay together with all that new found boost, and RPM's Think about it. Don
     
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    Don Onimus, Sep 14, 2009
  4. altered boy

    altered boy Outlaw Altered

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    canter for the win!! skip the blower and buy some pulleys big boy
     
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    altered boy, Sep 14, 2009
  5. big blue oval

    big blue oval Member

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    question, could you make the same boost with the screw, but be gentler on the bottom end?
     
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    big blue oval, Sep 14, 2009
  6. Mike Canter

    Mike Canter Top Dragster
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    A screw don't work unless it has RPM. A Rootes will work well at lower RPM. I think the answer is now it would not be gentle down low because you would have a lot of tire shake if you ran a screw at a lower RPM.
     
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    Mike Canter, Sep 14, 2009
  7. KennyKeller

    KennyKeller New Member

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    Mike
    Can you tell me what changes other than fuel need to be made to switch to a screw?
    526 Aires,14 degree big chief SSI HH. I'm only turning the motor 8000 rpm.
    Thanks
    Kenny
     
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    KennyKeller, Sep 15, 2009
  8. JustinatAce

    JustinatAce Member

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    Awww. C'mon Mike, you could run the screw, it would just take a crank pulley the size of a medium pizza and a blower pulley not much bigger than the quill shaft. :)
     
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    JustinatAce, Sep 15, 2009
  9. Mike Canter

    Mike Canter Top Dragster
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    Kenny, the first thing is you most likely need a larger fuel pump for the screw than the Rootes and with a screw blower you do not use High Speed Bypass you use a Low Speed Lean Out during the time in first gear then shut it off when shifting to second gear. You also don't want to lean it out in high gear and make sure it has plenty of fuel in high gear. Without this Low Gear Lean Out you will have constant tire shake and may damage the motor around the 1000ft mark. There are modifications required to the V slot in the Barrel Valve for idle. Also you don't use as many hat nozzles because the blower doesn't have to be lubricated or cooled as much. The basic fuel setup changes are all in the PSI Blower Manual,
     
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    Mike Canter, Sep 15, 2009
  10. Money Shot

    Money Shot Member

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    screw vs. roots

    I was not necessarily trying to make max power by switching to a screw. I was looking at the efficiency of the screw vs. the roots at the same O.D. Seems at the same O.D. one may pick up more power and be easier on the bottom end. Just a thought.
     
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    Money Shot, Sep 15, 2009
  11. KennyKeller

    KennyKeller New Member

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    This was my thoughts also.
    mike, I will get back with you after while, I've got a bunch of work to do.
    Thanks
    Kenny
     
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    KennyKeller, Sep 15, 2009
  12. AFC357

    AFC357 New Member

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    I like the Screw over the Roots as I don't have to strip a blower every week anymore! The blower is also more a "constant" as opposed to a "variable" in the tune-up;)
     
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    AFC357, Sep 15, 2009
  13. john348

    john348 Top Alcohol

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    I have to agree on that
    I think the blower is the only piece of the car i have not worked my butt off on all year...
     
    #13
    john348, Sep 15, 2009
  14. Mike Canter

    Mike Canter Top Dragster
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    Money Shot...there is no way you could run a screw at 20% OD. It would have almost no boost. The only way to make boost now is to launch at 6000+ rpm and hit 10500 rpm.
     
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    Mike Canter, Sep 15, 2009
  15. Money Shot

    Money Shot Member

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    screw vs. roots


    OK, Thats What I needed to know. So a screw isnt even comparable to a roots in terms of eye to eye. Never have ran a screw or known anyone that has one. Good info. So it would seem that the screw is for folks who want the (next level) in performance. Im certainly not there.
     
    #15
    Money Shot, Sep 15, 2009
  16. Mike Canter

    Mike Canter Top Dragster
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    No you can not run one the same as the other. For what you are doing the high helix is probably the best. I don't know what RPM you are shifting at with only 20% OD but if it is less than 8000 you have a ton of potential left in that motor by upping the OD to 30% or 35% and/or bringing that shift RPM up. There is a lot of difference in performance between shifting at 7500 and 8500 and a ton more going up to 9000 rpm. It can be a whole new experience especialy with the OD turned up. The first time we ran a blower car we were at 33% OD and was shifting at 8000 and said wow. Then we went to 45% on shifted at 9500 and it was a whole new car and experience.
     
    #16
    Mike Canter, Sep 15, 2009

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