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

2M views 12K replies 2K participants last post by  WRX-maniac 
#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





 
#7,707 ·
"Im sort of curious to see the ages of the members who post about bov's. Im thinking that if you want the bov sound, you may be somewhere between 16-20 and if you think getting a bov is ricey, you may be in the 21+ age group. I just think that the bov sound is something that seems more appealing to the younger wrx owners out there and that you grow out of it with age. Im just curious thats all."

I'm 18 and I hate BOVs. I have one but it is most definently recirculated. They annoy me because people run around and feel they need them to get people to notice their car. Most of the time if someone has a vented BOV, thats all they have done to their car so there is no reason to show off. my .02
but you are right i would probably say... MOST... people who have vented BOVs are probably younger. They need to be educated.
 
#7,716 ·
a cat back alone adds no power. a turbo back does. most of the wrx's around my area with exhaust have full exhaust. stock exhaust is restrictive. but im getting us off the all important topic of 99% of members being proven wrong about BOVs. please wagon, go on and tell us how the BOV died for our sins but christians couldnt have a savior made of aluminum so they renamed it "jesus".
 
#7,719 ·
You know what I do to get attention? I swing the turn wide when parking and crash into the car next to me. That really makes this awesome metallic scraping noise! And best of all its free!!! If anyones around they all look at you, its a cool way to say "hey look at the cool wrx over here". IMO anyways...
 
#7,721 ·
Go to Nabisco. This website does not need know it all cocky members. There are plenty over there for you to join with. I don't see how you justify coming over here with you forty some posts and try to make people on this board who have thousands of posts sound like idiots. They are smart because they have more experience with wrx's than you ever will.
 
#7,723 ·
i think its the fact that they dont sound like anything else, they are i distinct sound that you easily recognize... no other plain four turbo'd or not has the same growl...
 
#7,724 ·
Great thread!

I don't post a lot .

This is my first turbo car so I am learning.

I'm an "older" guy I guess, and I do like the Psst sound.

Plus I thought it made my car faster:eek:

But after reading all this, my BOV is coming off!

Thanks guys for the info!

WR
 
#7,725 ·
This whole ''CAR SCENE'' is gay. People who try and look cool with there car is gay. When the BOV blows off no one around you thinks your cool. No matter what you do to a WRX it is still ''Rice''. If its not rice then wtf is it? When ppl say: ''Yo dawg i just got my JDM lip in the mail foo". you cant say thats not rice.

I love cars but i hate the people who drive em.
 
#7,730 ·
Oh my Goodness. First off you wrote: ''Im an older guy''. The comment i made was sarcastic because there seems to be alot of totally awesome teens drivin the subies and getting LED's and BOV's. I never attacked you in any way so you need to take a chill pill.
 
#7,740 ·
The reason why our cars do not like them is because we use a bpv to recirculate air instead of venting it to the atmosphere. It already accounts for the recirculated airflow when determining the right amount of fuel to mix with the air. If you vent instead of recirculate, then the mix will be incorrect and that leads to poor performance and possible harm to your engine.
 
#7,742 ·
In the future please use the SEARCH function for these type of questions.

Lets use a simple math problem to explain this.

Intake brings in 10 units of air. MAF sensor tells the ECU that 10 are coming.
BOV releases say 3 units of air.
therefore only 7 units of air are sent into the engine.
ECU sends in 10 units of gasoline thanks to the MAF sensor reading.
There are now 3 units more of gas in the engine.

You are running rich. This causes poor idle, pausing between shifts, etc.
 
#7,744 ·
I think it is interesting that people don't usually talk about the down side to the OEM BPV. When the PBV opens, it is releasing air that has all ready been sent through the turbo and heated up, and puts it right back in front of the turbo to be heated up again.

On older WRX's I don't think a 100% Atmo dump valve is terribly bad. Yes, you are releasing air that has been metered, but how long do you think it takes the computer to catch up? Most likely a second or less I would think.

Now, on the 2006 + WRX, the tuning and fact that they have air injection you have to run 100% recirc. or you will run into idle issues.

I think that you are fine using a 50/50 BPV on the 2.0 liter WRX's. I have been using one for about 10,000 miles with no issues at all with idle, etc.
 
#7,748 ·
I think it is interesting that people don't usually talk about the down side to the OEM BPV. When the PBV opens, it is releasing air that has all ready been sent through the turbo and heated up, and puts it right back in front of the turbo to be heated up again.
That "hot" air is already metered and accounted for as you are closing the throttle plate - this air is not running under a significant load where hotter temps would be considered more of an 'avoidance of knock' issue. The goal here to to be sure that the air/fuel mixture is proper so that it is more completely comsumed in the ignition-combustion process. The goal being to avoid issues such as cylinder wash which lead to increased resistance, temps, and oil consumption.

On older WRX's I don't think a 100% Atmo dump valve is terribly bad. Yes, you are releasing air that has been metered, but how long do you think it takes the computer to catch up? Most likely a second or less I would think.

Now, on the 2006 + WRX, the tuning and fact that they have air injection you have to run 100% recirc. or you will run into idle issues.

I think that you are fine using a 50/50 BPV on the 2.0 liter WRX's. I have been using one for about 10,000 miles with no issues at all with idle, etc.
Do you have an A/F gauge with wideband sensor? If not you cannot make this claim as you have no way to measure the results. If you do though - please let us know what you have seen. I am very curious about the resulting ratios off throttle when the pressure is equalizing.

Everything I have read however with MAF states that BOV's are a bad idea - using a partial mix is simply partially correcting the issue. In real world driving, I'm sure there are plenty of moments where you are going to run a bit richer than you should, the thing is you want to minimize that type of thing. You also certainly don't want this occuring any more because of a BOV - an item which does not add much in the way of performance (vs a BPV) and simply makes noise.
 
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