Blow Off Valve Splitter Diverter Valve For VW Audi 1.8T 2.7T GTI GLI 337 TT S4Blow Off Valve Splitter Diverter Valve For VW Audi 1. 8T 2. 7T MK4 Golf Jetta A4 Valve has an aluminum piston for fast response and high boost pressure durability. Valve is fully rebuildable and untable. This is a must have upgrade for stock or heavily modified engines. This is a hybrid BOV recirculation valve that has been designed to work with engines that have have metered air flow systems (Mass air flow sensor, MAF). Where a traditional BOV would