Easy to install and setup, the Turbosmart Dual Port BOV features sequential ports for quiet operation on mild boost and full performance at full boost. Half vent-to-atmosphere, half recirculating, offers multiple easy to change configurations. Also, The Dual Port can be configured as a Supersonic, Megasonic, Plumb Back or Dual Port making it Turbosmart's most versatile BOV. So the Dual Port can essentially be Four BOVs in ONE!