Stock our cars come with an electronically controlled Diverter valve not a BOV. BOV's are usually vacuum operated, but they both do the same thing. The problem with the stock unit, is the plunger/spring that keep it closed are pretty weak stock and it is a weak point for a boost leak at higher PSI's. So you're not gaining HP with an aftermarket one, as much as you are making sure that you don't have any boost leaks when you start making more power. Go Fast Bits make a insert (the DV+) that replaces the stock plunger/spring that is inside the stock DV, thus preventing boost leaks while maintaining the stock electronic operation.
So my next question is there an after market DV that doesn't deliberately make "the noise". I would like to upgrade the DV but not have the noise if I don't have too.
Yes you get a DV+ from Go fast bits and just keep the hose attached to the stock diverted valve that recirculates to the intake. That way you get the added benefit of the DV+ with no noise.
Blow off valve/bypass valve (aka BOV/BPV) holds pressure in the intake system when under boost, but releases it when not needed to prevent damage to the turbo. There are two primary styles, one that vents to atmosphere, and one that vents to a re-circulation tube. Generally a BOV is VTA, and a BPV is recirc. BOV will make noise when it vents, BPV is quiet since it vents back into the intake. Either style can be controlled either by the ECU or by vacuum.
