Only get recirculating blow off valves or diverter blow off valves. The HKS SSQ2 is ok as long as you recirculate it. Best blow off valve for the Evo is the JDM MR DV or Forge DV. I heard Tial 50mm was good too. As long as its recirculating or diverting; its ok. If not, you will encounter stalling issues when you're slowing down to a stop & your rpms will flutter below zero when your car has gone under some pressure like going up a hill or struggling to accelerate after you let go of the pedal. Same thing will happen also if you put a BLOW OFF VALVE backwards, so be aware. Most recirculating kits will make you relocate your wires and hoses. They should all have instructions, if not, take it to a pro(topspeed). I know the jdm mr dv holds efficiency up to 25psi.. Not sure about the others. I heard tials up around 30psi max. Stock U.S evo blow off valves are plastic and don't hold boost efficiency well(only about 14ibs). Only point in getting a aftermarket blow off valve is either because your modding quite a bit or you are going to raise the boost. My 2cents bro A cone filter or intake kit will help your turbo spool up some and also you can hear it more noticeably and can be aware if you are spooling too much or not spooling if you don't have a boost gauge.