Full recirculating BOV. The Plumb Back system recirculates all excess pressure back into the intake system. Great for enthusiasts who do not want to be noticed but want the performance and reliability benefits of a quality BOV.
 
Please note; 
When using this with a TTS Rotrex super charger kit please order the 25mm with 4-5mm reducer option
 
Two valves would be required for twin-turbo applications, such as the Audi S4 2.7L (B5) 97-01.