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"The BIG BOV thread" (Where all bov question threads get merged)

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#1 · (Edited by Moderator)
This is the big BOV thread. If you didn't find this thread, you didn't search.

This thread is where all BOV question threads get merged into.

The quote below in this first post is from our BOV info sticky and contains links to some very explanatory BOV information. Please take the time to explore the links before you ask repeated questions.

Thanks!


A stock WRX/STi comes with a BPV (Bypass valve) which is a vacuum-actuated valve designed to release pressure in the intake system when the throttle is lifted or closed. This air pressure is re-circulated back into the non-pressurized end of the intake before the turbo.

An after market blowoff valve (VTA) does basically the same thing BUT unlike the stock unit it releases air to the atmosphere (giving you the loud sound). Some people see an after market BOV on a stock WRX as being in poor taste (probably due to the fact that it is basically a noise maker that really as no other benefit), while others simply find the sound very attractive.

Proponent opinions notwithstanding, there is a small mechanical downside to having an after market BOV (VTA) on a stock WRX. The problem comes when releasing air to the atmosphere that has already been metered by the mass airflow sensor. When the BOV releases (blows off), the ECU will be injecting the wrong amount of fuel into the cylinders. The engine temporarily runs too rich (meaning too much fuel is injected into the cylinders). This temporary rich condition isn’t typically THAT harmful, but it may cause bucking or hesitation on lift-throttle as well as some other concerns outlined in the links below.


Links for BOV info:

Sinister's BOV FAQ

Wikipedia

Unabomber on Nasioc

Davenow on Nasioc





 
#2,712 ·
While some people claim to have experienced problems, most of the world is just fine w/a 100% atmo BOV. Basically the worst thing that should happen is that you'll shoot more flames out if you're catless. As long as the BOV isn't leaking air at idle or under boost, there is absolutely no reason it should affect MAF readings anytime but between shifts...

-Michael
 
#2,724 ·
The fluttering and chirping sound on the WRC cars in the ALS -- Anti-lag system. I am not going to go into ALS in detail, but it uses the ECU (exhaust valve timing IIRC) to keep the turbo spooled. Generally a turbo will not last very long with an ALS system running -- therefore it is not so good to run on the street.

-joe
 
#2,725 ·
NJwrbT-WRX said:
The fluttering and chirping sound on the WRC cars in the ALS -- Anti-lag system. I am not going to go into ALS in detail, but it uses the ECU (exhaust valve timing IIRC) to keep the turbo spooled. Generally a turbo will not last very long with an ALS system running -- therefore it is not so good to run on the street.

-joe
Yeah, ALS are the shiznit.
 
#2,726 ·
Cross-threaded BOV bolt = no more threads!

ummm whoops!

So im putting my IC back on, and was kind of in a rush to get it done. I ended up crossthreading one of the BOV bolts. :mad: I backed it out, and ended up with a handful of aluminum threads. :rolleyes:

The other BOV bolt is holding the BOV down for now. It seems to be sealing. I was thinking about drilling out the hole, re-tapping it for a larger bolt, and putting a larger bolt in. Good idea?
 
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