A Blow-Off Valve (BOV) is a pressure release system present in most turbocharged engines that prevents compressor surge by allowing the compressed air to vent to the atmosphere, making a distinct hissing sound, or re-circulated into the intake upstream of the compressor inlet. It keeps the turbocharger spinning when the throttle plate is fully closed. It is also specifically aimed at helping the turbocharged engine in question to maintain the same rev for a longer period (less than a second) when changing shifts. This way, the driver can get instant boost, reducing the lag and giving the optimal power just when needed. BOV also reduces wear on the turbocharger and engine.