Yeah, sorry. Actually that doesn't quite answer my query. I think I understand the principles of the BOV but it was more to do with the HKS one in particular. The sound of the pressure release seems to come from the air filter area, rather than the inlet manifold side where the actual valve is, or have I got it completely wrong?
That means its not working, or youve got a recirc one.
If its a normal ptchhhhh sound from the inlet its a recirc valve.
Its its flutter/chatter sound then the valve isnt working and its just doing what it would naturally do without a valve, and your hearing the pressurised air escaping back out the turbos when you let off.
Right, I've been under the bonnet today to try and suss things out. It's definately an HKS sequential BOV. It says so on the valve.
I'm not sure if what I did made any difference but I pushed the valve in with my fingers (engine off) and it seemed to 'pop' in, as if it was stuck. I started the engine and revved it a few times with my hand over the end of the BOV and it is definately working, so I took the car up the road. Noise still the same!
Is it possible that the noise I hear from the driving position is an intake 'suck' rather than the BOV dump??
Having said that, the car seems to pull smoother now. Maybe the BOV was stuck shut? I don't know. Happy days!