Turbosmart's Kompact Dual Port BOV will give you the performance you are looking for. Unlike the OEM plastic valves that use un-reinforced diaphragms and are known to crack under increased boost, the new Kompact valves use an O-Ring sealed piston which, coupled with their billet aluminium construction give them over 30PSI boost handling capability. If you are going to crank up the boost on your Focus ST, this upgrade is a must! Dual port mode allows air to be vented to atmosphere for sound without upsetting the ECU. Dual port mode can be switched off by adjusting a block off collar on the body.