PSI Roots

Discussion in 'PSI Superchargers Tech Questions' started by Peacemaker AFC, Sep 7, 2011.

  1. Peacemaker AFC

    Peacemaker AFC New Member

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    How much overdrive can you throw at a PSI Roots before it becomes inefficient. It is the newer one prob 4 years old never used. Going on top of 519 TFX with AJ heads. We used to spin our old lf 14-71HH 52 percent because it started pumping hot air. I have heard do not spin the PSI over 42 percent and am wondering why.
     
    #1
    Peacemaker AFC, Sep 7, 2011
  2. Mike Canter

    Mike Canter Top Dragster
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    Read my post below on the K-8 max speed. If you hit 10,000 rpm on the motor and have a 42% OD on the blower then how fast is the blower spinning.........could be that magic number of around 14,000 which is real close to 14,625 rpm and that is when the rotor tips go supersonic. That is probably where that 42% comes from. If you are not spinning your motor to 10,000 then compute from what you max rpm is to what the blower rpm is and make the overdrive bring it to 14,000 rpm. So if you only go to 9000 on the motor you can crank up the OD to 55% for a blower RPM of 13950.
     
    #2
    Mike Canter, Sep 7, 2011
  3. Peacemaker AFC

    Peacemaker AFC New Member

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    I usually turn it around 8000 just to be conservative on parts. The car runs 3.86 with an old 14-71 HH mert spinning 51 percent over. Going to stick the PSI Roots on a 519 motor with dart 96 heads. I was wondering if the reason behind his saying don't spin it over 42 percent is because it might outrun him im not sure never messed with a PSI before just got it brand new for less than 5 grand.
     
    #3
    Peacemaker AFC, Sep 12, 2011
  4. john348

    john348 Top Alcohol

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    Mike
    Not trying to start anything but
    How are you coming up with 14,625 things go SS
    Been a while since i did the math but i remember it being much higher than that to go SS
     
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    john348, Sep 12, 2011
  5. Mike Canter

    Mike Canter Top Dragster
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    Not me that came up with the critical speed of 14,625 rpm for a high helix Roots supercharger. That comes from all the supercharger manufactures and designers such as PSI, DMPE etc and from Patrick Hale. Not sure it is SS or just the volumetric efficiency just starts to drop real fast. Either way it appears that not much gained from going above it. There is the same problem with jet fighters and that there is an airspeed that they can't go above with the engines. With those jets the forward airspeed just pushes too much air into the intakes which is more than can digested through the engines so the efficiency drops off real fast. Dangerously fast.
     
    #5
    Mike Canter, Sep 12, 2011
  6. john348

    john348 Top Alcohol

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    just doing some quick math i think the rotors would have to go around 28,000 rpm to go SS
    I am sure it is volumetric efficiency falls off the cliff @14K
     
    #6
    john348, Sep 13, 2011
  7. aaa2643

    aaa2643 New Member

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    D psi

    So a what RPM does a "D" series PSI go backwards, or BAE cylinder heads stop flowing anymore air? 5,6 or 8 heads.

    Has anyone ever crunched these numbers to find out on a 511-521ci motors?

    Thanks, Steven
     
    #7
    aaa2643, Sep 22, 2011
  8. AlteredFan

    AlteredFan Member

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    Currently Crunching numbers aaa2643. Will get back to you soon.
     
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    AlteredFan, Sep 26, 2011

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