Exhaust Butterfly Valve

Discussion in 'Thunderbird' started by PDeak, Jun 10, 2019.

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  1. PDeak

    PDeak New Member

    Jan 31, 2018
    1
    3
    Eysins, Switzerland
    Hello, I would like to understand the function and the operation of the exhaust butterfly valve inserted in the left exhaust pipe of my Thunderbird Commander. If for whatever reason this is efficient, why only in one of the pipes, why not in both of them. Any advice appreciated.
     
  2. Helmut Visor

    Helmut Visor Put on your big boy pants and man up
    Subscriber

    Oct 3, 2018
    1,524
    750
    Three Counties
    Hi PDeak, and welcome in :cool::cool: no idea I'm afraid :confused::confused:
     
  3. PDeak

    PDeak New Member

    Jan 31, 2018
    1
    3
    Eysins, Switzerland
    Thanks Helmut Visor. In the meantime I found a quite reasonable explanation.
    QUOTE --- The purpose of this system according to the motorcycle manufacturers’ marketing departments is to create back-pressure at lower RPM’s to increase torque. Unfortunately, this probably isn’t the real reason; the true purpose of the exup valves is to meet noise and emissions regulations. The exhaust valves are partially closed at idle and low rpm to reduce noise, and closed again at the upper RPMs to meet peak noise and emissions regulations. The proof of this has been shown on the dyno where removing the valves and retuning the engine creates a flatter better torque curve. --- UNQUOTE
    It still doesn't explain why only one system I/o two :-(
     
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  4. dilligaf

    dilligaf GrrrR3Rrrr
    Subscriber

    Mar 30, 2017
    7,216
    1,000
    Washington Tyne & Wear
    Hi mate and welcome
     
  5. Recmech

    Recmech New Member
    Subscriber

    Dec 10, 2018
    19
    3
    Pilbara Western Australia
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