Understand and the comment not to use stock bov was for high boost application although some have seen it leaking under normal boosting (19-20 psi).

 

FWIW, I have an HKS SSQV on my car.. VTA and Recirculated versions.. Both work "ok" but flutters too much at part throttle, and definitely caused surging under some driving conditions.. I always hated the sound, but I finally am completely fed up with the sound and am going to a 1G Version of the FORGE DV and recirculating back to the intake, even though I don't have to (My blowthrough MAF sensor is after the DV) I want my quiet back..

 

Yeah, actually on my car I discovered why it would leak at higher boost.. Many of us use the DV line to tap for boost controllers or gauges, not all of those devices are completely "Closed loop" and tend to leak a bit of pressure out of them.. When you do that, your not getting enough pressure to the diaphragm to keep it closed at much higher pressure..

The stock idle vacuum on the car is about -7psi (20in/hg) the spring on the stock valve is 10psi therefore it generally stays closed except under lift and deceleration when the internal pressure of the Intercooler pipe overcomes the spring pressure assisted by the engine vacuum at the manifold.. Under boost, yoou have to maintain a tight seal to keep it from leaking, so you have the 10psi, plus boost pressure.. but the surface area of the diaphragm and the size of the hose going to the boost means that the actual pressure to hold the valve closed is about 2/3 the boost pressure plus spring pressure.. so if you boost at 20psi, then the pressure is about 13psi + 10psi 23psi.. If you have a weak signal to the DV, then the valve isn't securely closed and will whistle and leak.. so you raise the spring pressure slightly and/or fix the vacuum/boost line issue..