Adjusting your BOV or BPV


Each Blow-Off Valve (BOV) or Bypass Valve (BPV) needs to be adjusted to suit the vehicle it is being mounted on. The aim of the adjustment on Vee Ports, Supersonics and Dual Ports is to make sure that the piston is hard closed at idle and that the piston closes fast enough to minimise backfiring and not stall the engine. Plumb back BOVs are equipped with a spring which are designed to keep the piston open at engine idle and hence the cap can be left in the middle position.

Adjustment to the BOV is made by rotating the cap. To increase the spring force on the piston, rotate the cap clockwise in the direction of hard as marked on the top of the cap. To decrease the spring force on the piston, rotate the cap anticlockwise in the direction of soft as marked on the top of the cap.


CAUTION – Do not rotate the cap beyond the first O-Ring indicator groove

• Start with the BOV cap at the maximum soft position (The indicator O-Ring should be completely covered by the edge of the cap)

• With the engine at idle the exhaust port should be closed off by the piston – the piston should be hard against the seat and not floating or moving

• Free rev the engine and back off quickly, the engine should return to normal idle speed – if the engine drops below idle or stalls increase the spring tension by one turn

• Repeat this process until the engine free revs and returns to normal idle speed

• Test drive the car and ensure that when decelerating or changing gears that the engine has minimal backfiring and no stalling. If backfiring is excessive or stalling is noticed then check all connections made during the installation, otherwise increase the spring tension

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4 thoughts on “Adjusting your BOV or BPV

  1. Hey ive got a 2004 wrx and ive installed one of these on it but doesnt matter how soft or hard the spring is it will always backfire and the revs go up n down from idle to 1500 3 times than settles. My engine runs at 19 PSI. Is that normal ??

  2. So I just bought a car with a plumb back turbosmart adjustable bov. Are you saying that the cap needs to be rotated and positioned half way between full hard and full soft, or does it need to be specifically adjusted like the other bov’s ?

    • Hi Craig,

      It will need to be specifically adjusted like other BOVs, however being a plumb back your car will be less sensitive to it being set ‘soft’.

      • Thanks. Been getting some stalling and backfiring so I’ll give it a tweak.