SOoo, you want to vent your BOV? - Subaru WRX Forum
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post #1 of 2 Old 02-02-2005, 09:19 PM Thread Starter
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SOoo, you want to vent your BOV?

It would seem over the years, the same problem arises. "I want to vent my BOV so everyone can hear that great sound" ... But there is one problem, you tried it and your car bucks and farts, or worse, it threw a cell. There seems to be a misconception as to why this happens. Some say it is cause the recirculating helps keep the turbo turbine spinning, some say it is turbo lag...these are all wrong. Let me make it as simple as I can. The answer is because like many other cars, it has a mass air sensor. This meter tells the ECU how much air the engine has coming into it and adjust the fuel for the correct air/ fuel ratio. No matter what, if you are venting, this is happening to some degree, some more noticeable than others.

So you are venting, you are at full throttle, you go to shift. The throttle closes, and the BOV opens. Now here is where it happens, The ECU has no way of knowing that the BOV released any air. So it is still sending in the amount of fuel it thinks it needs. And of course with that air gone, and all that fuel, cause a very rich condition for a moment. Thus the bucking and farting.
But there is hope.
option 1: Get rid of the mass air sensor all together. And go with stand alone engine management. This will allow the engine to run with a "air speed density system" or a load type system. It will use a sensor it check the manifold pressure, and adjust accordingly. Plus the tuning can be endless for any setup. Problem is is that setups can be up to the $3000 range. And you better sure as hell better know how to tune a motor,or know someone that does. So option one is not for everyone.

option 2: "this one is my favorite" Install a dual discharge BOV. What this little thing does is release air form two different points at once. So some air will go to the atmosphere, and some will go back into the intake. This will allow just enough air back into the intake to prevent the bucking. Granted, it will still cause a rich condition, but brief enough the motor will not stumble. Companies such as GFB, Turbosmart, and others are out there and well worth the money.

I hope this allows some insight to the problem and allows you all to get what you want form your car....happy boosting

Patrick "The Dr." Riveira
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post #2 of 2 Old 02-03-2005, 04:15 PM
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Just to add something to Patrick's article - this is quite common on turbo cars with MAS systems. Many people want to show off the fact that they have a turbocharged car and don't realize that they're causing a rich condition in between shifts.

When you shift, the BOV releases the excess boost pressure to the atmosphere instead of back into the intake system where the MAS expects it to. You're basically messing up the ECU's calibration of air/fuel ratio when you do this. Is it harmful? Not very, but your car will not be running at an optimum level. It's a trade off. What's more important to you - being flashy and attracting attention or making your car run the best it can? Of course, if you switch to a stand alone ECU, these problems are all erased.

-Chris Founder
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