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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





 
#7,527 ·
Until you're pushing big numbers, I would pass on the BOV and CAI for now.

Put your money towards better use: Catless uppipe + downpipe + exhaust + engine management. :thumbup:

Here are some tasty links for you to devour:
The "Good first mods" sticky
And here's great coverage of FAQs from NASIOC.
 
#7,528 ·
BOV - no, there are NO positive effects besides sound. Even over 20psi it is better to have a recirculating valve. You will run rich w/ a BOV.

I run the stock valve w/ 19psi and I have a VF-34 Turbo

CAI - no, there are NO positive effects besides sound compared to the stocker (you pay for sound more than the few HP that you gain from the lean condition it creates). Also, most intakes for the WRX are harmful b/c of the bend that effects where the MAF is located and will give the ECU incorrect readings. The only time you need a Short Ram Intake for the WRX is w/ a Front Mount Intercooler b/c it wont fit any other way.
 
#7,529 ·
i got an adjustment knob for ya, it involves two 12mm bolts and a recirculation hose.

Anywho, no, thats pretty much the only way. Why urs doesnt have it? no clue. But the stocker doesnt need to be adjusted. :thumbup: :thumbup:

Although its probably just a screw, ghetto rig it, your motor wont like you soon anyway.
 
#7,532 ·
armysti said:
i had a hks bov on my stage 2 wrx, and i had no problems with it.... do u ever wonder that the reason people have problems with it is because they some how dont install it right? i dont know to each his own....
Theres also diffrent sized ones. Some put a BOV on a car not knowing how much PSi the car is pushing. The UNIVERSAL BOV's is where I can see there being a problem aswell, in this case adding spacers and stonger springs to the BOV is needed to work well with the car all round, and this is where things go wrong alot.
 
#7,534 ·
BOV for stock 06 wrx

do i need a bov for a stock wrx? i dont drive it hard on the street but i do bracket race it at the drag strip. i come out of the hole walking it out at about 2 grand (2.0) 60 foot, and shift at 5500 rpm the rest of the way down the track for a 14.3 et at about 96 mph. since im doing this to the car do i need a bov? let me know...thanks
 
#7,536 ·
I'd say you definately need a BOV...and probably a CAI if you are bracket racing it at those times. The BOV would work best with a MBC (manual boost controller), but a BOV and CAI is fine at this point. In order of mods you need from most important down it would be: 1. BOV 2. CAI 3. MBC......glad I could help!
 
#7,537 ·
speedDman1 said:
I'd say you definately need a BOV...and probably a CAI if you are bracket racing it at those times. The BOV would work best with a MBC (manual boost controller), but a BOV and CAI is fine at this point. In order of mods you need from most important down it would be: 1. BOV 2. CAI 3. MBC......glad I could help!
:rotfl: That was harsh, but it was a good point. Try to do a search before you post a thread. There are lots of threads that talk about how bad all of the mods mentioned above are. BTW a blowoff valve makes you engine run rich between shifts, and can lead to a crappy idle. There is no performance advantage of a blow off valve as opposed to the stock by pass valve
 
#7,538 ·
yes don't listen to these people! BOV are the shizzle! the rich conditions they create between shifts give you an extra 40hp at least! and that hissing sound every time you shift is even better!!!


waahhhhhhhhhhhhhhhhhhhhhhhhhh pppttttssssssssst wahhhhhhhhhhhhhhhhh pptttssssst wahhhhhhhh!

11 second car, get a K&N cold air intake, they are the best out there, and manual boost controler and then you'll be beating everythign on the street.:thumbup:
 
#7,546 ·
my car came with a really cheap BOV... and its pretty much awful..... but i don't have a recirc valve to replace it.. so if you're gonna buy one.. the ssqv is actually one of the best ones you can buy... i have a couple buddies with dsms that use them, and it doesn't hurt anything.. but its mostly for the sound,.. alot of the cheaper ones leak, and don't have any purpose beside making you run richer.. so if you like one, i'd say buy it, but make sure its not a cheap, badly manufactured one.. i know mine leaks.. :(
 
#7,547 ·
negative, the APS 50/50 recirc valve is the absolute best aftermarket bov hybrid on the market. It recircs 50 percent into the system again and blows off 50 percent to atmosphere...its the safest for our cars due to this. You can get this part from rallysportdirect.com or pretty much any tuner site dedicated to subarus.

Its also completly tune friendly...it doesnt have to be 50/50...i believe you can make it any ratio you want...60/40 perhaps...depends on your setup and needs.
 
#7,549 ·
Touge Daimao said:
Over the weekend, I bought the Apexi Twin chamber adjustable BOV...i believe it is 100% atmospheric...will this one be bad for my suby?
Yes. Did you not read the links I posted and the advice everyone gave you? Why bother asking a question if you're just gonna do it anyway?
 
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