Bosch diverter valve (BOV) is good to very high PSI rates if it's installed correctly.
I have seen so many turned the wrong way it's not even funny anymore however.
You have to keep it so boost pressure holds it closed, and intake vacume allows it to flutter open and allows air to leak past it.
If you have it bassackwards, it will leak and flow when you don't want it to.
Here is an old pic of my dual Bosch BOV setup. use two Porsche Diverter Valves, they were about 30.00 each IIRC.
Notice how they are both arranged so they face "up" when installed. When you get this valve, try this. Blow through both sides. Your going to notice that you can blow air through the valve barely if you blow at the bottem fitting. If you try and blow through the side fitting, you can't get any air through at all. (Reason is the air pressure is helping to seat the valve, and the more pressure you add, the more it just stays closed. The other side is true however, it wants to allow air to leak by, and is solely closed by spring pressure alone. Low spring pressure at that.)
Under intake vac. conditions, it pulls this valve open, and allows the pressure to divert back into the intake pipe, blowing on the compressor wheel, and keeping boost up between shifts for example.
A very cool side effect of this larger valve is the bypassed air get's a short cut to your engine from the filter. This helps with throttle response I belive due to better low speed air flow.
