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.
ok...so i finally go my Forge 100% atm BOV today and installed it....
the install was pretty easy...even in 20 degree weather...
so i took it out for a drive and it really is just like everyone says....
when sitting at idle there are no problems what so ever...runs just like stock...
when you are into boost it lets off a nice solid pssshhhhh....very nice...though i think i am going to go the route that aussieinstlouis went and get a stiffer spring so that it is not letting off as easily...
to give you an idea of how loud it is...when i had a cd playing at vol level 6 you could just hear it over the music...when i turned it up to 9 you really had to listen for it....
i am very pleased...when i get my ecutek in a month or so i will be sure to flash the ecu with 100% atm bov and there should be no worries...
so now everyone should run out and buy one
it runs just like stock....if not a little better...
The colour is the way they differentiate the 'stiffness' of the spring. I found it was opening venting too easily for my tastes and called them - they said 'no worries' you need a stronger spring - call George at Forge Motorsports USA and he sent it to me the next day.
I have had my car for almost a year and made a few mods. The thing is now that i hear a new loud noise when I start boosting over 5psi. i took the car to the dealership and they thought it was an exhaust leak, my intake or boost gauge, but billed me for disconnecting my boost gauge, stating that was makin the noise and the problem. they also did a diagnostics on my engine the day before. Only mass air flow showed up.So i left the dealership and the noise was still there. i got my money back and they hooked the gauge back up, but they were pissed about doin that. I know it is not my intake since that was my first mod 9 months agoand familiar with the noise it makes. The dealership said i modded my car too much for them to work on. The noise starts when i accel rapidly in 1st and 2nd from 5 psi on and from 9psi in 3rd to 5th. I am hoping it is my BOV since it is comin from that area as far as I can hear. I have never heard my BOV and it is the stock one. Am I right that its causing the noise or is it somethin else. It sounds like a shoosh with a whistle to it. Please help
the noise is there whether cold or hot. If I drive normally and let it boost slowly there is no noise. Only when I hard accel. i installed my uppipe 2 months ago and the noise wsn't there after I installed it. just the CEl for mass air flow. i thought it was from the AEM Alternator pulley, the sound wasn't present after I installed the pulley either, but I took that off and the noise is still there.
there is no way thats an uppipe leak, if it was leaking for that long, the gasket would be destroyed and it would be leaking all the time. An uppipe leak of that magnitude sounds almost like an bird squaking or somthing annoyingly loud. the swoosh with whistle is not your bov, it is your nice little turbo, the sound is being amplified by that injen intake you are running. dont worry about it, just enjoy the sound of power.
I installed the HKS SSQV 100% atm valve several weeks ago and boy did it make my car run like absolute CRAP. I took it off the following day. There was less throttle response, and 2nd gear felt like I was towing a 1000lb weight behind the car... it sounded cool, but d@mn!
I then bought a GFB BOV and installed it 50/50. The car runs better than it did with the stock one. I have no explanation for this, and I have already taken crap for the statement so dont bother. My throttle response has improved with the GFB and boost seems to hold better between shifts. Actually, GFB makes these claims in the instructions that came with the valve and I cannot dispute them. I'm also not one of those people who is overly optimistic about this sort of thing. I always assume nothing is going to work... I am VERY pleased with the GFB in 50/50. It doesn't make noise unless you get into the throttle. I think when shifting very gently it vents little or nothing at all. The valve is actually 60/40 by the way. GFB also says the valve flows 54% more air than the stock bypass... for whatever thats worth.
Are you sure it is the turbo. I have had the car with the mods I have listed below for the last 2 months and the noise just appeared a week ago. One thing i forgot to mention was that the mechanic said it might be my wastegate not opening up or stayin open..I can't remember. But he stated this before even lookin at my car. i just don't want to hurt her..she is all I got. if it is just the turbo handeling her business then I am all smiles, but if not then I am one unlucky WRX owner
okay i just picked up my Forge BOV from UPS and installed it at my work's parking lot. Now I don't know too much about BOVs' so here are some questions for you all. For some reason I can only hear the "sound" when I shift 1-2 & 2-3 @ high rpms >4. When I shift from 3-4 & 4-5 I don't hear a thing. Also, I don't hear the sound everytime I shift including downshifting. Is this normal or do I have a lemon? I don't have an aftermarket intake and I didn't do the intake silencer removal mod. I heard that the BOV "sound" would be louder if I did either one of those 2 mods. Lastly, there were 2 additional springs included, one red and one blue, and also a silver thin circular plate. Are these needed for the BOV or are they for modding the BOV to do something else?
The blue and red springs are the main spring options - I will bet that it is fitted with a yellow. You only need to change if you are having problems with venting. I know the blue is stiffer than yellow, but do not know where the red fits in the series -call George at Forge, he'll know.
This is where you need to understand what the BOV is doing.
You will not get 'the sound' on downshifts because you are not making boost.
The BOV relieves the pressure between the throttle and the turbo when the throttle plate closes.
When you are at WOT and full boost the turbo is making 15psi or more boost and flowing a lot of air. You take your foot off the gas and there is a lot of air that runs into the now closed throttle plate - if that does not escape your turbo can compressor stall due to the high pressure build-up.
The BOV sound is that air escaping. If you are not making large boost or none at all there is no reason for the BOV to open - hence NO sound!