You need a short sound clip of the sound, and then load it into the sound editor. Note the BOV sound is not a direct clip of the BOV, but the underlying noise (e.g. for the engine the noise is like a gunshot to simulate the ignition of air:fuel).
Ok ok .But that topic might be at Muscleadons
Here is my backfire BOV sound file Why you dirve with patch X .FBM is good car but i can't drive with it in S1 servers