See Fig 1A.Ī BOV releases pressure out to the atmosphere which is were the so called “cool” sound comes from. It is circulating air that has already been metered by the ECU. You also get smoother shifting.Ģ) What is the difference between a BPV and BOV.īoth valve types do exactly the same thing with one significant and important difference.Ī BPV releases pressure and circulates it back to the turbo inlet after the MAF sensor. Some beneficial side effects of employing a BPV/BOV in the design of an engine is noticeably less compressor speed deltas, which means the turbo will remain spooled longer because you don’t have pre-conceived pressures backing up against the turbine blades. By relieving the pressure you reduce this effect significantly. Compressor surge can be damaging to a turbo and significantly decrease its life. Here is a good explanation of compressor surge in section 1.1 of this paper. In the Subaru it is generally placed on the outlet end tank on the intercooler which is just before the throttle body.Ī BPV/BOV is meant to relieve excess pressure after the turbo as the throttle plate is shut rapidly to prevent excessive compressor surge or stall. Please read on.ġ) What is a Bypass Valve (BPV) or Blow Off Valve (BOV)Ī BPV/BOV is a valve that is placed in the air induction system of an engine and is specifically located after the outlet of the turbo and before the throttle plate and intake manifold.
#PLUMB BOB ACE HARDWARE UPGRADE#
Other mods may require you to upgrade to an after market unit but you will need to choose wisely. You absolutely get the best performance from the stock BPV on a stock car with a stock turbo. The induction system in a Subaru engine is precisely designed and making changes to this system with out clear purpose is counter intuitive. Because you want a cool sound is not a good reason. We will also discuss some tuning options and provide a guide for selection.īefore I continue with this section I will say this statement first… It is through many years of findings and real world experience, by many members of the STi community, that you should not replace your BPV unless you have a definite need to do so. I will attempt to shed light on the pros and cons and dispel some misconceptions. In this write up I will attempt to explain the purpose of a Bypass Valve/Blow Off Valve (BPV/BOV) and what the differences are and how and when one should be used over the other.