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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





 
#7,792 ·
:rotfl: :rotfl: :rotfl:

Dang It!! I clicked on that! lol
 
#7,793 ·
Your link doesnt work.....



Seriously though, he didnt ask whether or not a BOV was good he asked where he could get a flange. He already bought the damn thing so if he wants to put it on thats his business. Either help him or leave him alone.

To the OP: He is right though. You probably dont want that BOV on your car. As far as flanges, I could only find weld on flanges for greddy. Sorry.
 
#7,796 ·
For those thinking of a aftermarket BOV!!

I was experimenting with my car again using an aftermarket bov. I have been running a greddy bov atmospheric for a long time now and decided to see if switching to the stock bov would make the car run any better. And guess what, it did. Do not put an aftermarket BOV on your subie if you are running under 22 psi. The stock BOV more than adequate and makes a better pshht than the aftermarket did anyways. My car is tuned with around 240awh and runs about 18psi. With the greddy BOV i was always getting creeps and spikes and ran like ****e and burned way more gas. After switching to the stock the shifts are so smooth and have almost 0 creep and havnt had 1 spike yet. The recirc runs so much better for our cars than an atmospheric until highly tuned. The power pull has never been smoother. So i urge anyone who is thinking about an aftermarket BOV to reconsider and if you have already installed one, reintall the stock one back. if you are looking for an airhorne sound from a bov buy an srt4.
 
#7,798 ·
I was experimenting with my car again using an aftermarket bov. I have been running a greddy bov atmospheric for a long time now and decided to see if switching to the stock bov would make the car run any better. And guess what, it did. Do not put an aftermarket BOV on your subie if you are running under 22 psi. The stock BOV more than adequate and makes a better pshht than the aftermarket did anyways. My car is tuned with around 240awh and runs about 18psi. With the greddy BOV i was always getting creeps and spikes and ran like ****e and burned way more gas. After switching to the stock the shifts are so smooth and have almost 0 creep and havnt had 1 spike yet. The recirc runs so much better for our cars than an atmospheric until highly tuned. The power pull has never been smoother. So i urge anyone who is thinking about an aftermarket BOV to reconsider and if you have already installed one, reintall the stock one back. if you are looking for an airhorne sound from a bov buy an srt4.
Thank you Captain Obvious.

No seriously, Im glad you warned us all about the dangers of BOV's, since this exact subject doesnt come up EVERY SINGLE DAY in this forum, and we all have no clue how horrible they really are..... we owe you a world of thanks.
 
#7,805 ·
BOV dilemma

What's up all... I recently picked up an 02 wrx sedan with some upgrades. I am not really sure what the previous owner has done to it because I bought it from a dealer. From what I can tell it only has a few performance upgrades including a TXS bov and a Blitz nur spec cat-back. I am pretty sure that it has some kind of suspension kit because it looks like it sits a little lower than stock (although it does have RSL 18" elites):thumbup: .

The main question I have for you guys is; is the bov worth keeping or does it do more harm than good? I like the sound, but if it really is hurting the engine then I will just go back to stock for now. I have read through the stickys in the forum, but I would like some opinions on the subject. Please don't bash too hard, it's an honest question.

By the way, I will post pics asap.

Thanks
 
#7,806 ·
Most people on here will tell you that you should go back to the stock bypass valve. If you like the sound of the blow off valve, i would suggest you remove the intake silencer when you re-install the stock bpv. This makes the stock bypass valve more audible. If you search, you will find instructions on how to do remove the intake silencer.
 
#7,809 ·
Like I said in my post, I have read the sticky and was wondering what everybody's opinion was on the subject; Maybe it was you that missed something...:confused:

Although I am no expert on these engines, I do not see how an aftermarket bov would hurt the car. I could see the possible decrease in gas mileage, but to harm the engine by simply depriving the engine of air (richening the mixture) is what I don't understand. Is there something else going on that I am not thinking about?

No offense to Chromatica, but this is an honest question in which I am looking for additional information from what is posted in the short section of the sticky.
 
#7,812 ·
Its not going to blow up your car but 90% of the time it does cause drivability problems due to incorrect adjusment,poor designs,and less than optimal performance.If actually understand how a MAF system works this might be more clear.Why atmosperic BOV cuase less than optimal performance.. http://www.spdusa.com/blow-off_valves.htm
 
#7,810 ·
Like a few guys already said, your best bet would be to go back to the stock BOV until you need a new one. Some people run BOV's without problems, Some have alot of problems, I had the Rfl bov on my WRX when I was stock and I would turn on my car and it would stall right back out sometimes.
 
#7,816 ·
Thank You. That was much more informative than the sticky that is in this forum. I am really not trying to stir up any problems or make enemies around here, so don't take my post the wrong way. I was confused and did not know that the BOV is different from the BPV. Like I said before, I am not an expert by any means with this vehicle and I am only trying to learn. This is the reason why I wanted to post on this subject. I think that anybody needing info about this will get a great deal of help now.:thumbup:
 
#7,818 ·
no offense but your going to get flamed pretty quick here with that question. A BOV is not the best mod at all, it can even hurt performance. try exhaust components first, or even EM. also please read the stickies on the engine forum you will learn a great deal.
 
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