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It appears that there is a lot of confusion going around about the bypass valve, the sounds it makes, and the job it is there to do. We'd like to clear things up so that you are aware of the way the OEM valve works, and how a tune or aftermarket components can affect it.

Introduction to your OEM BPV

The Focus ST has an integrated bypass valve that is attached to the compressor side of the turbocharger. This valve is actuated by a solenoid which is controlled by the ECU. The ECU has a very specific set of opening, closing, and timer settings for the OEM valve. These settings allow the valve to operate efficiently under various levels of airflow, boost, and vacuum. When certain changes are made to the calibration that can affect these settings, the bypass valve may no longer sound the same or perform in the same fashion. This does not necessarily mean there is anything wrong, but improper settings could potentially be damaging. From the factory the bypass valve makes a very smooth "pshhh" style sound during a free-rev, light throttle, or between shifts after WOT. Under certain conditions there may be slight sounds of flutter if the valve is opened and closed quickly, or unopened at all. Ultimately, the smooth "pshhh" sound is preferred, but may not always be the result in all conditions.

Doing work!

The bypass valve has a primary job, to relieve pressure when the throttle blade is closed. It can also help offset pressure when the throttle blade is partially closed. Let’s call the stock valve OEM John. To begin working OEM John must be told when to clock in and clock out. To do his job correctly OEM John also needs to be told how long he should perform, and how aggressive the schedule is to complete his tasks. He has no mind of his own, and must conform to these instructions. If the instructions are incorrect, he knows no different and will continue to do what he was told regardless of the outcome. This means that when OEM John is fired and replaced with aftermarket Josh who has been provided the same instruction set, the outcome may not be correct. This is where we come in.

Up and coming

With your feedback we have revisited the operation of the OEM bypass valve and investigated the behavior from select upgraded valves. We were able to optimize the OEM bypass valve settings to achieve the signature sound people have grown to love from the stock tune while maintaining the rapid boost response from our OTS strategy. While these new settings may work for aftermarket valves, additional tuning may be required to achieve similar results. We will be including these new settings for the OEM valve with an upcoming firmware update along with our latest tuning strategy changes in v103 of our calibrations. You can expect to see these very soon!

The Tuning Solution

We understand that as the aftermarket develops we need to continue our research and provide tuning solutions for those looking to upgrade components that may not be supported by our OTS calibrations. This means we go back into the ECU from time to time to further dissect the complex relationships that exist to control these systems. As a result of this continued dedication we are able to offer what other tuning companies cannot; support and knowledge! Our upcoming Accesstuner Pro, and soon to follow Accesstuner Race software will grow with your feedback, suggestions, and with the aftermarket. Our tuning software has the most complete table assortment, documentation, and dedicated support staff to ensure you will always have the tools needed to tackle any build. COBB provides a complete tuning solution from start to finish.

Thank you for your time,
-Braden @ COBB
 

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Yeah I will update when available. In Cobb's post it's saying that the flutter is only sometimes but I'm getting all the time.
I don't get the flutter all the time, but I do get it most of the time. I'm not sure if the valve is closing too soon causing higher than desired boost and has to be re-opened immediately, or if the valve is opening too soon (loosing boost) and has to be re-closed, but it sounds like Cobb will have an improvement in the v103 maps. Hopefully the flutter is not overworking the valve. It seems like I recall I got the flutter even before the Cobb tune though, and didn't really notice it until after I put in the Green Filter. Will the v103 maps actually improve performance for this specific issue, or is it just for aural aesthetics?
 

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I must have missed the discussion about the sound of the BPV. Is this tune going to improve the sound so we can actually hear the stock BPV or is this just to fix the sound for those with open filters? i.e.: those that can hear the BPV...cause I'm all stock and it's silent.
 

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I must have missed the discussion about the sound of the BPV. Is this tune going to improve the sound so we can actually hear the stock BPV or is this just to fix the sound for those with open filters? i.e.: those that can hear the BPV...cause I'm all stock and it's silent.
Green filter people.

I hear it flutter under lower boost levels. With WOT there's a single loud burst when shifting (everyone wants that all the time).
 

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I emailed Cobb about this and talked to Eric...he said that v103 is to make aftermarket valve more compatible with the tune...but just stated "units in general" and did not state Forge valves specifically. But he did say to run the lighter spring as the heavier one will not allow the valve to open fully. I emailed Forge on which spring is lighter the one that was installed or the one in the bag but haven't heard back yet. I am probably overthinking this I just want everything to be correct for power and engine safety....
 

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I know Cobb V103 fixes the flutter issue an also Randy at FSWerks got a new file which makes the DPV work correctly.
 

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Running Steeda CAI and tune I get the flutter when in say 3rd or 4th at lower rpm and go WOT. Basically going from low > high RPMS it flutters until the gear shift, then you hear the normal whoosh
 
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