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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





 
#7,901 ·
Nobody actually has anything to point to the long term affects but having A/F ratio messed up.

Im still not convinced its that detrimental to the engine, maybe your cats but thats all.

BOV has a real good purpose, rather then recirculating warm air back into the intake thus reducing the temperature you vent it to the atmosphere and use fresh intake air only.
 
#7,902 ·
if you have an aftermarket exhaust.....put a BOV on your car and you will be spitting flames and making noise. Then put back your stock BPV and you will not have that whoooosh noise but with the silencer delete it will take car of that, but anyways the stocker will not make your car pop or spit flames.
 
#7,913 ·
What blow off valve to get ???

I want to make it so that when i shift my blow off valve is a little louder. So the pppssshh sound is alot louder. To make that louder would i need a new BOV ?? Some people tell me not to put an aftermarket BOV on a stock STI and then some people tell me if i want it to be louder than to put a cone filter on it ??? What should i do ??? Is it true that aftermarket BOV's arent good for our cars ???
 
#7,915 ·
In a nutshell, yes, aftermarket BOV are bad for subarus. I would reccomend the intake silencer delete, which is also known as the snorkus delete. It makes the stock bypass valve much more aduible and does not sacrafice driveability. If you search about BOVs or the intake silencer delete, you will find very valuable information on both.
 
#7,918 ·
I'm wanting to remove my recirc hose and plug up the hole in the intake. I'm wondering if this is a good or bad idea and if it will hurt anything because a friend with a 90 something talon said his stock recirc was in the same basic place and he had a/f problems.
 
#7,931 ·
yes this is true, you will run lean when you shift. You will get more performance if you keep the recirc hose, less spool up time every time you shift, rather than vent to atmo. The only benefit to taking it off is that you will hear that famous "Fast & Furious" WHOOOS every time you shift. Just get a short ram intake, or do the silencer delete mod.
 
#7,924 ·
I just installed the Perrin turbo inlet and my stock bov is very very loud now. I recomened just doing this + the snorkus delete, It will actually add power an sounds great too. Get the Samco turbo inlet though, older model perrins may collapse after 22psi, not to mention it is a harder install due to fitement issues. But if you are dead set on a BOV turbo smart has a 100% recirculatory bov that sounds great and won't drastically effect you negativly, it is pricy though ~ $300, but it is the best, absolutely no leaking like turbo xs and hks.
 
#7,937 ·
you could get an intake, but that could possibly cause problems with your air/fuel ratio and make the car run crappy. I would remove the intake silencer. It is free and it will give you the bov sound that you so desperately desire. You can even add a pannel (sp?) filter, not a cone filter, such as a K&N. That supposedly makes the stock bypass valve more aduible as well.
 
#7,938 ·
Well that flaming wasn't a bad as I thought it might be :rotfl:

If you're desd set on getting a BOV then check these out

http://www.gofastbits.com/index.php...cts&sub_option=bovs&sub_sub_option=stealth_fx

The Stealth FX or Deceptor will both vent to atmo and recirc the air. You can set it to any ratio in between. Have it recircluating enough to appease the ECU but still have enough venting to please your rice requirements.

Best part is that it will bolt straight onto the factory TMIC
 
#7,940 ·
Can anyone enlighten me on why the SSQV BOV is bad for WRXs?
They don't recirculate without the recirculation kit...which in turn screws up the ECU because the MAF isn't reading the amount of air coming into the intake that its supposed to...etc etc etc...makes you run rich between shifts which in turn can harm an engine in the long run, etc etc etc...run a search. You will get TONS of info there...you don't need a vent to atmosphere BOV unless you are running at least 300+ HP to the wheels, when you really start accruing some boost. The stock BPVs are good up until about 20-22psi's of boost...which unless you upgrade your turbo...you shouldn't see.
 
#7,948 ·
i guess i have been bamboozled. At my local tuning shop, ( i won't mention any names) one of their techs assured me that the HKS SSQV is the absolute best BOV that i can get for my WRX. he said that it would only prolong the the life of the engine and give me that great sound (that part is true though). so how long do you guys think before i see any adverse affects if i keep the HKS BOV on my car? (in terms of miles, years, whatever)
 
#7,949 ·
I would call them on it. Either tell them you have done a lot of research (printout relevant statements) or ask them to prove why the HKS is the best - aside from the best one that makes them $ that is. Ask them to "trade" the HKS on something more useful. The Subaru BOV really is the best choice.
 
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