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Help me understand the stock BOV and solenoid issue and solutions

16K views 24 replies 9 participants last post by  Chinaman_Chong 
#1 ·
I've been reading up on this stuff and I'm still confused and unclear of it all.

Here's my attempt to lay out what I have found to be the issue and what some claim to be the solution.

When reading the following, please assume the car in question is a completely stock BK2 2.0T:

The issue: The BOV solenoid tells the BOV to blow off boost at certain RPMs as a safety measure as seen in this video: https://www.youtube.com/watch?v=38CRpKQCh0Q

The solution: Bypass the BOV solenoid and run the BOV straight off of the intake manifold. This will make the BOV hold boost and not blow off boost pressure until you lift off the gas.

Am I getting this right?

Is it truly unsafe to bypass the BOV solenoid?

Synapse claims that their BOV is the only BOV fast enough to work with the stock solenoid (see: https://www.youtube.com/watch?v=yj44QfAx_Qw). Does that mean the Synapse BOV will hold boost all the way to redline even when ran off the solenoid?

I'm open to a discussion about this topic as I am just trying to get a true understanding of everything that's going on and to obtain a solution that is safe while also performing at a high level (holding boost until letting off the gas). Any insight, advice, and sharing of experience is welcome.

Thanks!
 
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#5 ·
Does that mean the Synapse BOV will hold boost all the way to redline even when ran off the solenoid?
In short, nope.

The ECU will still command the solenoid to open the BOV as it sees fit (IE for safety precaution). ECU uses the bov solenoid along with the EWG (electronic wastegate) to minimize or totally stop things like boost spike and make a more linear torque curve, which in turn makes a more mundane driving experience.

I need to do the bypass too one of these days, I get part-throttle/low rpm blowoff like a mother****er with my HKS SSQV.
 
#10 ·
I simply bypassed the stock solenoid, car pulls much better personally.
 
#24 ·
I have a couple videos about this, including the HKS BOV install. I've ran it that way for years and it is solid. I tapped into the intake manifold (bypassed that dumb solenoid).
 
#25 · (Edited)
A BOV has one main functional purpose. As your turbo creates boost leading into the engine, it travels through your intercooler and stays in the system. This boost is allowed into the engine through the throttle body. As you step on the gas, the TB opens. When you let go of the gas the TB closes. Once the TB is closed. The pressurized air in the system needs somewhere to go. A turbo is designed for air to go one way, and one way only. The turbo is spun by the exhaust gases, and is connected to the compressor wheel by a shaft that spins at 1:1 to the exhaust gases. Once your TB is closed, if the air has no where to go, it will try to leave the way it came in: through the turbo. The compressor wheel is spinning in one direction only. If the air is forced through the compressor, you get what is called compressor surge. This essentially slows down the compressor wheel and makes it eventually stop and spin in the opposite direction. This puts stress on the turbo as the turbine and the compressor are now fighting each other in opposite directions.

This is where a bov comes in. The bov vents this boost so it does not go back into the turbo. When you let go of the gas, the TB should close, and consequently the BOV should open venting all the boost and preventing compressor surge. The faster your BOV opens, the less strain you put on the turbine shaft.

To my understanding, there are two types of BOVs. There is a push type and a pull type bov.
The stock bov is a push type. It relies a spring to push and hold the bov closed. The spring is delicately balanced so that with enough vacuum, it will open up. The stock line you see on the bov creates vacuum, and it is enough to overcome the strength of the spring and open up allowing the boost to escape. A push type BOV can leak very easily as excess boost will simply push the spring open and cause a leak. Which is why many upgrade to an aftermarket BOV with a stronger spring, or adjustable springs.

The pull type bov relies solely on boost pressure to stay closed. The more boost you have in the system, the more it will stay closed. Pull type bovs typically hold boost much better, as the way they are designed, increased boost helps keep the bov closed. Increasing boost will only keep it closed even more. they still require the vaccuum line to open up, but do not rely on a spring to stay closed.
Synapse is a pull type bov. They have designed theirs in a way that the oem solenoid is enough to open theirs up quickly and effectively.

The OEM solenoid is designed to actuate just the bov, and is dedicated for that purpose only. It has vacuum ready to open the BOV when the ecu demands it. This vacuum is consistent and does not change, and in some cases is not enough to open a bov quickly(think aftermarket with a strong spring)

The manifold vacuum line is just that, it takes the vacuum from the manifold, which comes naturally once the TB closes and the engine consumes all the air. It is not controlled by the ecu.

Hopefully this clears some things up as far as understanding the mechanics of this car.
 
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