The Turbosmart Dual-Port BOV is a Hybrid-type BOV offering three BOV's in one.
 
The Turbosmart Dual Port BOV can be configured to vent to the atmosphere, back into the air intake (full recirculating) or both! Plumb Back system for quiet, road-compliant operation, Supersonic for the race track, or Dual Port (50/50) for the best of both worlds.

APPLICATION: Fits Subaru WRX MY01-MY07, STi MY01-08.

SUPPLIED WITH: Mounting flange, blanking plug

Turbosmart Part # FG-BOV-WRXDP-S

Turbosmart Blow-Off Valve (BOV) FAQ

Q: What does a Blow-Off Valve do?

A:  A BOV's function is to release excess boost pressure from teh intake system when the throttle is closed.  A perfect example of this is during on boost gear changes.  Without a BOV, upon shutting the throttle, the pressurised air caught between the free spinning turbo and the shut throttle is forced back through the turbine blades.  This in turn forces the turbine to slow down or stall.  This phenomenon is often referred to as "compressor surge", or "cavetation" and it places undue load on the turbocharger bearings, significantly shortening the lifespan of the turbo, or even causing serious damage.

The secondary function of a BOV is to reduce the "turbo lag" effect between gear changes.  Without a BOV, the compressor surge slows the turbine down, which then takes longer to spool up again when the throttle is opened.  With a BOV, the excess boost pressure is released, keeping the turbine spinning and thus reducing the turbo lag effect.

Q: How does a Blow-Off Valve work?

A:  A BOV is usually mounted on the intercooler pipework between the turbocharger compressor and the throttle body, ideally on the throttle body side of the intercooler.  A vacuum line connects the upper chamber of the BOV with a vacuum/boost source from teh intake manifold.  In its resting position, a spring holds the piston shut against the intake port.

Under boost with the throttle open, the Blow-Off Valve remains shut.  Upon shutting the throttle, vacuum is created in the inlet manifold.  This vacuum combined with the pressure in the intercooler pipe forces the piston to open, releasing excess boost pressure in the intake system.

Q: Are BOV's only for high performance cars?

A: No. All turbo-charged cars can benefit from having a BOV installed, both as a performance modification, and to prolong the life of the turbo.

Q: I hear a "fluttering" sound when I shift sometimes, is that bad?

A:  The "flutter" occurs when upon shutting the throttle, air is caught between the turbo's compressor and the closed throttle plate.  The consequent back pressure forces the air back through the turbine blades.  This process, more commonly called "cavetation" places enormous loads on the turbo and can lead to premature wear of the turbo bearings and other load-bearing components. 

The cavitation, or "flutter" can be fixed by either fitting a blow-off valve onto a system that doesn't have one, or making sure the blow-off valve is matched to the output of the turbo and is not working outside its flow capacity and ensuring th eblow-off valve is set up correctly.  In short, this "flutter" no matter how nice it may sound, is a sign of a problem, and if left uncorrected, might result in a rather expensive turbo rebuild.