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BPV useful for twin-screw / roots?

Discussion in 'The Blower Bistro' started by mlackke, Sep 30, 2018.

  1. mlackke

    mlackke New Member Established Member

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    So I have been trying to understand benefit of BPV for twin-screw/roots, but getting bit mixed info. So as for turbos & centrifugal superchargers it is clear that BPV is needed, but how about when talking twin-screw / roots style SC's? My understanding these styles SC, when TB is closed, the intake vacuum opens BPV for direct path for air from manifold to SC intake (after TB).

    So it's clear that this will lower IAT since there is no air SC to push and air will go directly to intake bypassing SC completely when BPV is open.

    However my question is, does BPV have any else benefit, i mean can you run eg 20psi of boost without BPV long as your IAT in idle are ok? Or is there some scenarios where running high boost twin-screw/roots will damage SC if run without BPV?
     
  2. slo984now

    slo984now AKA 01yellerCobra Established Member

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    There's no way to run any supercharger without a BPV of some sort. Anytime the rotors are spinning it's pressuring air. That air has to go somewhere.
     
  3. gt347mustang

    gt347mustang Well-Known Member Established Member

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    Are you considering deleting the bpv?

    I'm trying to understand why you would ask this in the first place.
     
  4. mlackke

    mlackke New Member Established Member

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    Let me ask this way, if you run twin scroll with out bpv, what situation and what damage will would occur?

    I assume all comes down when running full throttle, then suddely releasing throttle would surely cause problem with turbos, etc. But twinscrolls/roots because TB is before SC, releasing throttele will close TB and in same preventing excessive air to go supercharger/manifold.
     
  5. mlackke

    mlackke New Member Established Member

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    Actually opposite. Eg i did see KB2.1L 96-98 cobra kit does not include BPV, (dont know why since all other kb kits have). So i`m thinking is it mandatory to add bpv to ensure SC proper functionality.
     
  6. slo984now

    slo984now AKA 01yellerCobra Established Member

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    There's still pressure there. Even after the TB. The BPV also keeps the IAT's down as pressurized air gets hot.
     
  7. mlackke

    mlackke New Member Established Member

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    Correct if I'm wrong but when TB closes, engine runs idle, so SC is not producing boost almost at all?

    But still if I ask question:
    "if you run twin scroll/roots with out bpv, what situation and what damage would occur..and specially why?

    Anywhere explanation/video explain this. EG with turbos this video is very clear what happens:
     
  8. 01blckcobra

    01blckcobra Member Established Member

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    Once you close the throttle there is still positive pressure. idle and WOT. Bypass valve releases that pressure. At WOT and the throttle is shutdown quickly, If enough pressure it built spiked, it can actually lock-up the supercharger and/or engine.


    Basically same principle as the turbocharger/ centi.
    Move the turbocharge to the intake manifold. Now you pressure is built after the TB not Before.. Now you Have to move the BPV to the side that makes pressure.

    There's many reasons why it's there....
     
    Last edited: Oct 26, 2018

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