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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





 
#32 ·
Turbo XS BOV

Does anybody fid this BOV to really make shifting a chore? It seems that there is a reall fall in RPM so you have to really think to give it some more gas befreo you shift to the next gear otherwise you get lag...


Seems like it makes shifting harder...

Also it makes my muffler all dirty with the dripping unburned gas...
 
#36 · (Edited)
Yes. The car already has a bypass valve which can be replaced with an aftermarket valve (either bypass or blowoff type).

The differences are bypass vents back to intake and is generally pretty quiet. Blowoff vents to atmosphere and is generally louder.

BPV keeps stock design. BOV isn't like stock. Word is some BOVs can cause CEL. BPVs will not.

I have the Forge BPV.
 
#10,946 ·
I just bought my car and it happened to come with the Forge BPV as well. The thing is, you mentioned that some BOV's can cause the CEL to appear. Could this also be the case for BPV's as well? Just a random question. Because whenever I get on it a little, and by little I mean to 5K RPM average, the CEL comes on with a blinking cruise control light. It's confusing. I'm going to run a diagnostic scan to see what code it could be but for craps and giggles, I figured I might as well ask.
 
#38 ·
CEL = check engine light. Just tells you somethings not right.

My understanding is that the BPV vents air back in that the MAF told the ECU is already there. So no problem. BPVs are also claimed to reduce lag when getting back on the throttle after shifts and such due to air being put back before the turbo.

However with a BOV, the air is no longer vented back to the intake and instead out to the open. So it can confuse the ECU. I'm not sure what exactly the code is people are getting. BOVs usually sound better.
 
#39 ·
Si2WRX said:
BPV keeps stock design. BOV isn't like stock. Word is some BOVs can cause CEL. BPVs will not.

I have the Forge BPV.
This is completely incorrect. I know of no BOV on the market that will cause any CE lights unless it was installed improperly. I am using the Blitz BOV and it works flawlessly.
 
#40 ·
Thanx SiR And God...
God you are using it on the stock turbo right?...and does anyone have ne links for where i can parts for my 02 WRX? Such as a blow off valve...sorry...i am a real real big newbie with cars..haha..just happy to have such a great one.. :) thanx..

BlaZiaNWrX
 
#42 ·
If there is no CEL issues, then I stand corrected. But I wouldn't say such if there were for no reason. Users on i-club have had such experiences. But as you said they could or could not be due to installation.

God sells parts. Vividracing.com sells parts.
 
#51 ·
Forge BOV noise???

I recently installed a Forge atmospheric BOV. When I'm driving the car and let off the throttle I hear a stuttering, multiple "psst, psst, psst, psst" instead of one quick "psst". I assume this means I have the wrong spring in the valve. Does this mean the spring is too strong or too weak? I was told the valve had the blue spring. Has anyone experienced this noise and if so, what spring/spacer combo have you had to use to fix this?

thanks,

Punk
 
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