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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





 
#2,377 ·
yeh, but arent 50/50 valves less expensive then 100% atmospheric ones? i totally agree with you on the fact that they dont function quite as they claim, but ask anyone whos had a 50/50, or whos had both...a 50/50 is quieter. so im sure theres some air getting recirculated. some is better then none as far as im concerned. i guess they really are useless on a stock turbo, but they're just cool to have. a lot of people who buy subarus buy them because there not a common car. granted the dynamics of the car (awd, turbo, price) out-weigh that, but the fact still stands that we dont fit in with the honda croud, and all the other common tuners. with that comes attention. if your going to get attention anyway, why not do it with a bang, or a pssssft, or anything else. we stand out no matter what. and no matter what anybody says, when they see a turbo car go by and pssssft as it shifts, i dont care who you are, about 90% of tuners will think thats cool s*** even if they know its sort of a waste. my .02
 
#2,379 ·
" I never recommend 50/50 valves since they do not function as they claim. The air will always go to the path of least resistance which is the atmosphere so in essence they aren't really 50/50 despite the manufacturer claim."

This is NOT true(no offence god). Have you ever examined a gfb 50/50 hybrid bov? If you have, you would notice that the recirc opening is closer to the intercooler then the atmospheric opening. This means that on small amounts of blow off, it might only use the recirc. Also, since the turbo is spinning between gears, there is a vacume in the recirc hose, and that makes it the path of least resistence(I could be wrong though)... I am not saying that a 100% atmospheric bov isn't good for a wrx(and am no expert so I wouldn't), but I know how my bov works, and it does a pretty good job. Maybe since you never put 50/50 bov's on cars, you really don't know if they work the way they claim....... Whatever.

peace
 
#2,382 ·
"I know the GFB screws on the top tend to fall out and cause a boost leak"

What does that mean? The ones with the adjustable sound leak boost? Or the screws fall out of the gfb bov's and then they leak boost? Either way, I wouldn't know cause I have a gfb and no screws have fallen out, and it isn't the adjustable sound one... whatever though:)...
 
#2,383 ·
those of you with a TXS TMIC, what BOV do you use? im having problems..

here is the deal. I have a brand new TXS V2 TMIC. I have a GFB Bov. at first i got some weird sounds. Now with the stock TMIC i never had a leak or anything like that. Im trying to determine whether it is the gasket or the bov itself not being flush with the aftermarket tmic. I tightened the bolts and the sound went away but it sounds like i might get a slight leak at about 3-4psi. how would this effect performance? it seems to pull like crazy and has no problem making boost etc. maybe its just how it sounds with an upgraded tmic? its a very quiet air sound. what would you suggest? its set to 50/50. i dont want to go back to stock + my stocker is broken from tightening. any solutions you can suggest?

thanks for your time
 
#2,384 ·
Worx Tuning BOV flutter...

i put on the worx bov yesterday, and when i boost less than 1.0 bar, once i release the throttle, it makes a fluttering noise. i have a blitz sus, and with the stock bpv, it would just "woosh" even without full boost. i tried a couple different spring settings, but they all have the same flutter. anyone else with this bov have the same problem? im wondering if i just have to let it break in properly or if it needs more lube...:(
 
#2,388 ·
i believe wastegate flutter ususally occurs when you are building boost.

happasaiyan mentioned that he is getting the sound when he releases the throttle. this is usually compressor surge as mentioned in the link thread that i posted above.
 
#2,389 ·
"i believe wastegate flutter ususally occurs when you are building boost."

this is incorrect. the wastegate stays closed while building boost, or the turbo would not build boost. The wastegate opens when the pressure in the vacume line going to the wastegate solenoid gets to a certain point. If you take your foot off the gas with pressure(let's say above 4psi) the ecu will want to lower boost all the way. So the bcs closes and the wastegate opens and closes......this is wastegate flutter. It also happens when the boost peaks and the wastegate has to control the boost. I am not saying that his problem isn't compressor surge, I just don't think it is:). I think he just hears the wastegate....

peace
 
#2,392 ·
"The wastegate opens around 9psi, so it opens while building boost. Just not immediately."

This is not true either(from what I know). I mean certain wastegate actuators open at certain pressures, but depending on the setup, you can be running 17psi without the wastegate being open at all. It all depends on how you tune your car. Ony my car, I can tell when the wastegate opens, and it DOES NOT open anywhere b4 10psi unless I take my foot off the gas.

peace
 
#2,393 ·
its not the wastegate. i know what my wastegate flutter sounds like, and this is not it. you will only hear the wastegate fluttering as your foot is on the throttle, and like wrc_obsessed said, its only when i lift my foot off the throttle. it is being caused by the bov, as i have learned from worx themselves. they said its just a distinct sound that their bov makes. might change as it gets broken in...i guess well just see.
 
#2,396 ·
"you will only hear the wastegate fluttering as your foot is on the throttle, and like wrc_obsessed said, its only when i lift my foot off the throttle."

so you're sayin that if you are at 9psi of boost, and you take your foot off the gas, the wastegate won't open? Also, like I said, depending on the setup, you can make it so the wastegate doesn't open til 30psi if you want.... whatever though:).

peace
 
#2,398 ·
I am not looking for it to be louder, i am having a problem with my boosting. This is the only after market thing I can find on my car. I was told that adjusting it may help with the problem.

Problem: Just say 40mph 2nd gear... I floor it. The boost gauge will go to about .12 bar, drop down to maybe .07 bar then back up to about .11. Basically until it levels off, but it causes power surging that's really annoying. Is that normal?
 
#2,400 ·
Hippy:

The wastegate doesn't open AT ALL when you lift off the throttle. The ECU doesn't try to release boost by opening the wastegate. The car tries to release boost pressure during shifts while maintaining the spool of the turbo so you can get back on boost as soon as possible when you depress the accelerator after the shift. If you opened the wastegate during a shift, you'd have to rebuild all the momentum of the turbine all over again. It is the BOV that releases the boost pressure to avoid compressor stall and potential turbo damage. The wastegate remains closed to keep the turbo spinning.

Also, the stock wastegate opens at around 8psi. That's not to say that you can't change it. A stiffer wastegate spring will keep the gate closed until 15psi, or 17psi, or 30 psi. A boost controller can prevent the wastegate from opening at all.

Please do a bit more reading. I don't like cleaning up after your misinformation.
 
#2,401 ·
Hey happasaiyan

I was looking at the Worx tuning BOV and really like the way it works, and it seems like one of the best working BOV's available. I just would like to know how it sounds, because on their site the sound file is recorded like Inside the engine bay so it sounds really weird. Is it loud? Does it blow off everytime you let off the throttle no matter what boost you are at? Thanks! :)
 
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