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.
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.
It can also cause problems with catalytic convertors for those that are running them,when the unburned fuel ignites inside them.Also as well when the air is recirculated it keeps the turbo spining by a pinwheel effect and also keeps the chargepipes and intercooler pressurized.http://www.spdusa.com/blow-off_valves.htm same stuff can be found in a book called "Maximum Boost" by Corky Bell.
The running rich caused by a BOV isn't gonna hurt anything. It won't damage your cat, it isn't gonna kill your plugs, etc. However, it does happen. I had a forge BOV on my car for a long time and I absolutely noticed it. Wanna experience it yourself?
Find a nice sweeping offramp and get down it hard. As you're mid corner, lift your foot off the gas to make the BOV open, and then hit the gas again really quickly (you're simulating making an adjustment midcorner with the throttle, but I'm not telling you to go fast enough that you have to). If you're at any decent boost pressure when you lift, you will feel the car hesitate everytime you do this... If you don't feel it, your bov isn't working correctly.
I have a datalog somewhere that shows very clearly the richness when you get off the gas. It's inevitable based on how the car meters air... You can deny all you want and say what ever makes you feel best, but at the end of the day it is what it is...
Trust me I hate BOV's and they make the car run like doo doo. I'm installing my FP18g with Helix 820cc's and a Walbro 255, and last of all my Helix TMIC, within the next week or so. I'm getting it tuned with utec around 20-22psi, and I know the stock one doesn't like anything over 20psi at all, and 20 is pushing it at that. Should I stay with a recirculating valve or would atmospheric be ok with this setup?. I was either thinking a Forge Recirc, Perrin Recirc, or maybe a GFB Hybrid 50/50 to be even louder and more obnoxious. What would be the best/safest/smartest?
or you can search NASIOC for stock BPV mod. It uses a directional control valve to lock the BPV shut during high boost runs. I believe I will do this with the new setup.
21lbs on the stocker but I couldnt run any higher. Find out what boost you are going to run and that will determine if you need to switch. Then again the stock BPV can crack open at 19psi and others can hold till 23psi so Id say get a BPV just to be safe.
APS Dual Port or Turbosmart BOV, the later actually makes it very easy to adjust how much gets vented back to the intake. All you have to do is twist the cap on it as opposed to APS, where you have to take the top part off.
Stock bypass valve is also fine, although, personally I prefer aftermarket parts just because I hate stock.
the APS does not have to be taken apart to be adjusted, it takes only a hex wrench that is supplied. You should only have to adjust it once, during initial installation & thats it. The % of vent is not adjustable.
Can we try a temporary swear filter on the letters BOV? It would be funny as hell and also lessen the amount of BOV, CAI, MBC on my stock WRX threads. They did that to the letter SRT4 on my other site IWSTi.com and it was pretty funny, so whaddaythink?
Im not a fan of Perrin parts. Not worth what you pay for IMO, but Im just going with my experience. APS products, although a little pricey, usually fit perfect and work flawlessly. Sure there are cases where APS products fail, but their fit and quality and second to none.
I was talking to the rep at the local tuner shop and he said that puting a BOV in (to replace the re-circulating valve) would cause the engine to run rich and may lead to quite a few problems down the line. I have a stock WRX and i am buying a cat back exhaust...i was also gonna get the BOV, but now I am not sure...anyone got any advice??
My next step is going to be a mild turbo upgrade (along with pump, injecters) and maybe a CAI. (if any of you have any pointers on this topice please comment)...basically, i want more HP, but do NOT want to fail emmissions. Not sure how much i can do really.
You will tend to run a little rich between shifts with a bov,but i don't see any harm in it. I have a hks ssqv on my car,i had it when i had a tmic now i'm running a fmic with it with a vf-34 with all supporting mods.I will say i have been dyno-tuned on my utec with it,but still i had it on my tmic not tuned with no problems. From what i understand the stock bpv can hold up to 20psi anyway, and a crushed one a little more.For what's it's worth all my buddy's that have wrx's have one with no apparent issues.
i see most hks BOV's have that black knob to adjust with.for some reason mine dont have it.is there any other way to adjust it?my car runs fine so dont bash me on havin one haha..
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