The two types are recirculating or atmospheric,the one your looking for is atmospheric because of the pressure being realeased into the atmosphere which gives u that awesome sound I used the hks ssq on my wrx which I was pushing 20psi from a vf39 turbo and I currently have one on my sr20 swapped 240sx. But a bov does put more stress on the engine by having it constantly make up for the boost being released thus it should be used on high boost apps but u don't have to. Greddy,hks,blitz,and forge all make universal blow off valves greddy gives u nice wooshing sounds and hks ssq gives a nice woosh/whistle sound.