September 19, 2011 Products

How to Adjust a Blow-off Valve (BOV) or Bypass Valve (BPV)?

Before You Adjust a Blow-off Valve

Each Blow-Off Valve (BOV) or Bypass Valve (BPV) needs to be adjusted to suit the vehicle it is mounted on.

Vee Ports, Supersonics and Dual Ports 

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

Plumb Back BOVs are equipped with a spring that is designed to keep the piston open at engine idle. Hence, the cap can be left in the middle position.

How to adjust a Blow-off Valve? 

  1. Adjustment to the BOV is made by rotating the cap. This increases the spring force on the piston,
  2. Rotate the cap clockwise in the direction of hard as marked on the top of the cap.
  3. To decrease the spring force on the piston. Rotate the cap anti-clockwise 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


Quick and Easy Steps When Adjusting a BOV or BPV

  1. Start with the BOV cap at the maximum soft position. Note: The indicator O-Ring should be completely covered by the edge of the cap.
  2. With the engine at idle, the exhaust port should be closed off by the piston. Therefore the piston should be hard against the seat and not floating or moving.
  3. Free rev the engine and back off quickly. The engine should return to average idle speed, however, if the engine drops below idle or stalls. Go ahead and Increase the spring tension by one turn.
  4. Repeat this process until the engine free revs and returns to normal idle speed.
  5. 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. Make sure to check all connections made during the installation. Otherwise, increase the spring tension.