Newly Designed COBB LF Bypass Valve

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The bypass valve is a straightforward component that can be found in most turbocharged engines.  Its purpose is to relieve boost pressure in the intake tract when the throttle blade closes.  This is done to decrease wear on turbo and engine parts.  While this is a fairly simple task, leaks or inconsistencies in the operation of the bypass valve can occur.  These occurrences will diminish a car’s performance.  With that in mind, the COBB LF Bypass Valve (BPV) is a new revision with some key feature updates that ensure leak free, optimal operation through even the highest of boost pressures.

Piston Seal Comparison

piston seal comparison


The LF BPV features a piston o-ring seal that is twice the diameter of the old XLE design allowing more seal compression and reduced wear.  Not only is this the best safeguard against leaks, but in the unlikely event of an o-ring failure, o-ring sealing allows the unit to be easily rebuilt.   Adjustability of spring seat is no longer needed due to the updated spring and seal design which provides a 60% increase in clamping force at peak boost while maintaining similar operation at idle and transient loads.

Port Comparison

Port Comparison

The Subaru nose has also been redesigned to tuck tighter to the valve for easier installation.  Vacuum line routing has also been improved.  This updated design uses a banjo-fitting vacuum port which provides 360 degree adjustability of hose routing. This results in a simpler install and less potential leak points than the NPT ports used by the XLE unit.

Control Volume Comparison

control volume comparison

The new revision also reduces control volume by 30% allowing for extremely fast venting of boost when actuated.

Even the smallest inconsistency in the piston or mating surface can result in a leak.   This is why the COBB LF BPV is fully constructed with billet aluminum.  This process yields stronger parts that are made with a higher degree of precision than traditional cast methods.  The COBB LF BPV is still hard anodized and teflon coated which provides low sliding friction, reduces surface wear, and minimizes maintenance requirements.

Like the previous XLE BPV, this revision does not have the 50/50 block off plate which allowed for air to be vented.  This prevents rich fueling conditions for cars that are not properly equipped to vent air to the atmosphere.  Vehicles properly equipped with a speed density tuning strategy can simply remove the re-circulation hose making a fully vented to atmosphere blow-off valve.

SUBARU LF BPV WRX 2008-2014, FXT 2009-2013, OBXT/LGT 2005-2009, MAZDASPEED3 2007-2013, MAZDASPEED6 2006-2007

  • 2008-2014 Subaru Impreza WRX
  • 2009-2013 Subaru Forester XT
  • 2005-2009 Subaru Legacy GT
  • 2007-2013 Mazdaspeed3
  • 2006-2007 Mazdaspeed6



  • 2008-2015 Mitsubishi Lancer Evo X
  • 2008-2015 Lancer Ralliart

NISSAN LF BPV GT-R 2008-2018


  • 2008-2018 Nissan GT-R

SUBARU LF BPV WRX 2002-2007, STI 2004-2019, FXT 2006-2008


  • 2002-2007 Subaru WRX
  • 2006-2019 Subaru STI
  • 2006-2008 Subaru Forester XT

SUBARU LF BPV WRX 2015-2019, FXT 2014-2018


  • 2015-2019 Subaru WRX
  • 2014-2018 Subaru Forester XT


8 responses to “Newly Designed COBB LF Bypass Valve”

  1. I have a bmw 535i 2010 cobb tuner and now i have a hyundai veloster 2019 1.6 turbo any plans on coming out with tuning for my new car, please let me know what my options are.
    Look forward to hearing from you.

    • Hi Maximo,

      As it turns out, we do not have any plans to support the veloster. Sorry for the bad news.


  2. I just recently installed the LF BPV to my 08 WRX and was wondering if a tune was needed/recommend I am nearly all stock and cannot hear the BPV at work if you know what I mean

  3. Hi I purchased a Cobb updated LF BPV
    Car has a compatible new intake for the stock 2018 Sti and has the factory tune. Now “what does design reduces control volume by 30% allowing for extremely fast venting of boost when actuated”
    actually mean?. Will it function as a replacement to the stock BPV or will it just vent out sooner than the stock BPV. I could not find an answer.
    Ps I have not yet installed it yet

    • Hey Mario, that data point is essentially highlighting the LF BPVs ability to respond faster as the smaller control volume requires less pressure change in order for the valve to actuate. It is a direct replacement of the factory valve and does not require any tuning.


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