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Discussion Starter #1
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 (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. The rich condition can NOT be eliminated by engine management or tuning.


Links for BOV info:

Wikipedia

Unabomber on Nasioc

http://forums.nasioc.com/forums/showthread.php?t=1602235"]Davenow on Nasioc[/URL]






 

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Good Job on the Post TheJ!
 

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Discussion Starter #7
Is there a safe BOV to put on that will be noise wise different?
I guess that depends on what you mean by "safe"...

BOVs that vent 100% to the atmosphere on a stock WRX, really are not typically "THAT harmful".  Plenty of people drive 10s of thousands of miles and never suffer any noticeable problems (like blowing up), other than some hesitation/bucking on throttle lift or some extra popping/back fire  in exhaust.  Many people are really bothered though, by anything that inhibits the cars ability to run smoothly.  Some find less noticeable issues with a BOV that vents 50/50 (atmosphere/recirc).  Still others find that using an after market intake and leaving the stock BVP in place provides enough sound for them.

I guess it mostly comes down to a personal decision of what is more important to you.
1) The blow off sound that some find cool but others find cheesy?
2) Your car running as smoothly as possible and not negatively effecting your MPG while getting no power gain?
3) The money that could be spent on other mods that have more of a positive effect on power, handling, etc..?

If you do decide to go with an after market BOV, just make sure you keep your OEM BPV to put back before you try to trade/sell your car.  You will have much better luck trading/reselling the car later, if it does not seem to have been riced out.  Whether it logically follows or not, many people will assume that because of the BOV it was probably abused in some way.
 

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Is there a safe BOV to put on that will be noise wise different?
I guess that depends on what you mean by "safe"...

BOVs that vent 100% to the atmosphere on a stock WRX, really are not typically "THAT harmful". Plenty of people drive 10s of thousands of miles and never suffer any noticeable problems (like blowing up), other than some hesitation/bucking on throttle lift or some extra popping/back fire in exhaust. Many people are really bothered though, by anything that inhibits the cars ability to run smoothly. Some find less noticeable issues with a BOV that vents 50/50 (atmosphere/recirc). Still others find that using an after market intake and leaving the stock BVP in place provides enough sound for them.

I guess it mostly comes down to a personal decision of what is more important to you.
1) The blow off sound that some find cool but others find cheesy?
2) Your car running as smoothly as possible and not negatively effecting your MPG while getting no power gain?
3) The money that could be spent on other mods that have more of a positive effect on power, handling, etc..?

If you do decide to go with an after market BOV, just make sure you keep your OEM BPV to put back before you try to trade/sell your car. You will have much better luck trading/reselling the car later, if it does not seem to have been riced out. Whether it logically follows or not, many people will assume that because of the BOV it was probably abused in some way.
Thanks that helps a lot, if you get one that is a recirculating bov is that potentially harmful also? I like the the sound, I can see why some ppl find it cheesy though.

how about this one? http://www.rallitek.com/gfbblvalegth.html
 

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Discussion Starter #9
Thanks that helps a lot, if you get one that is a recirculating bov is that potentially harmful also? I like the the sound, I can see why some ppl find it cheesy though.

how about this one? http://www.rallitek.com/gfbblvalegth.html
I don't believe you will find a noticeable sound difference if you go with a full recirc (like the OEM BPV). The "hybrid" you are looking at there on a 50/50 setting will probably give you the best compromise. I can not personally attest to GFB BOV quality but to my knowledge GFB items are generally considered to be quality products.

Good luck!
 

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Well ill definitely be one to say replaces the air box with a cone filter made my BPV loud not as loud as some of those BOV's out there but you can definitely hear it inside and outside even with the music on
 

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it should be noted that bov's do serve a useful purpose high boost applications, it prevents the compressor wheel from coming to a screeching halt between shifts. Bov that vent to atmosphere are ok but recirculating it can help your turbo spool quicker. The stock bpv leaks badly when you start turning up the boost or so I've heard. Just my .02
 

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it should be noted that bov's do serve a useful purpose high boost applications, it prevents the compressor wheel from coming to a screeching halt between shifts. Bov that vent to atmosphere are ok but recirculating it can help your turbo spool quicker. The stock bpv leaks badly when you start turning up the boost or so I've heard. Just my .02
+1 agreed
 

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GFB makes pretty good stuff....it wasn't stupid loud and I never had any problems with the car acting up. Quite enjoyable!
 

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So if I install a new BOV, let's say the perrin one. I would have to have the AP in order for it to run right. ???
 

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It's up to you. If you get a BOV I would make sure to get a recirculating one. You really don't want to run a vent-to-atmosphere BOV, cuz that causes your engine to run rich and poorly. There are a few topics around discussing this more. But basically if you just buy another recirculating one you could just swap out the stock one for it w/o any problems, no need for an AP or tune. Only if you are venting to atmosphere(to get the loud sound) you will run into problems.
 
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