Evojkp,
The BOV will leak when generating boost on a part throttle when there is a bit less pressure on the diaphragm side of the valve than on the inlet side and it may bleed out a small amount of air at this point. It may also leak inwards a bit on idle when there is a very big vacuum in the plenum chamber. Fitting a stronger spring will help eliminate the leaks but will make the valve slower in acting and may IMHO cause potential problems with reverse air flow to the turbo (see the thread on reversing the dump valve for other peoples opinions on this)
Using an aftermarket vent-to-atmosphere (VTA) valve will mean that when the air is leaking in at idle it will be bypassing the airflow meter and the meter will therefore be reading the incorrect amount of air entering the engine (due to it not being able to record how much has entered) and the engine may idle very roughly and sometimes even stall.
This can be overcome with a VTA containing a stronger spring or a dual acting valve (like the HKS super sequential) that eliminates these problems. Note that by using a recirc valve, the idle problems do not happen because the air that is leaking into the valve has already passed the airflow meter.
Apart from that all a VTA gives is a nice whoosh noise which is good enough for some people......
Andy
.....Hopes he's got the right end of the stick now
