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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





 
#2,280 ·
In the instructions it said that the BOV was pre-set right out of the box. But the instructions also have a picture of a BOV being installed in an STi(the TMIC has the logo on it). Did any of you guys adjust you BOV, and if so please tell me by how much and the affect it had on your WRX. I've had mine for about a week and my gas mileage really sucks! Thanx:)
 
#2,281 ·
YeloFvr said:
In the instructions it said that the BOV was pre-set right out of the box. But the instructions also have a picture of a BOV being installed in an STi(the TMIC has the logo on it). Did any of you guys adjust you BOV, and if so please tell me by how much and the affect it had on your WRX. I've had mine for about a week and my gas mileage really sucks! Thanx:)
Don't adjust it. It's preset, just like you said. The reason your gas milage sucks is because you keep punching the gas so you can hear the BOV :D Stop doing that, and you'll notice that your milage didn't change...that's what I did :)
 
#2,287 ·
Quick question... I am installing my Bosal DP this week, and i am curious whether i have to worry about the 02 sensor. The third cat will stay, so that means i dont have to worry about relocation right??

Also i searched CEL eliminator and came up empty, any advice where to go? , i may have to tolerate a CEL for 2-3 weeks before my ECU is sent to Cobb
 
#2,288 ·
The rear 02 goes into the midpipe. So you don't have to worry about relocating.

Ya, just tolerate the CEL for a couple of weeks. But, make sure and tell Trey or Josh that you want that light gone. They only do it on request.
 
#2,289 ·
Did any of you guys replace the stock gaskets with new ones? I'm getting ScoobySport Uppipe, Downpipe, and Muffler in the mail this week and want to know if I should go get new gaskets (it's not coming with any)

Anyone have any idea WHAT gaskets I would need and where to get them? Thanks!
 
#2,291 ·
Where do I get new gaskets? I mean, do I just walk into my local dealer and say, "Hey man, I'm going to be voiding my warranty this weekend, and need a few gaskets. Can you hook me up?"

Any ideas?
 
#2,293 ·
Blow off Valves Worthless under 20PSI?

Guys, I was poking around on the internet and came across this article. Tell me what you think. I know its alot but it's interesting.

Real blow-off valves are used in high boost (20+ psi) to prevent the momentary rise in boost pressure of up to 50 psi from blowing out intercooler side tanks or popping off hoses when the throttle is shut. But at normal boost levels (under 18 psi) we can use the rush of over pressure to prevent our turbocharger from stalling all the time when we lift the throttle. This helps the turbo make better throttle response and boost quicker in real world conditions.

Enter the $35 by-pass (or priority valve) concept first developed on the AUDI rally cars and first introduced in the Audi Quattro Turbo and Porsche 944T. The very first Subaru EJ20 in 1989 also had this type valve. Your WRX has one also and we want you to keep it on your motor, unless there comes a reason to change it out.

The compressor by-pass valve is connected from the turbocharger compressor high pressure side (intercooler) back through to the low pressure side (the intake section) just ahead of the turbo compressor. When you close the throttle to shift gears this valve opens. It makes a loop of air back into the inlet with the boost spike of air pressure in the intercooler. Everyone has probably heard a blow-off valve go 'whoosh'. Well, we want that 'whoosh' to go right back to work keeping the turbo compressor wheel from slowing down. Instead of spending money on an aftermarket blow-off valve just to make noise, we leave the factory priority valve in place. Why?

The loop air flow effectively puts the turbocharger into a no load condition and the wheel keeps spinning. Under this very low load condition the high pressure air in the intercooler blows into the intake via the by-pass valve and pin-wheels compressor impeller. When the throttle is opened again, the turbine wheel is still spinning at a relatively high rpm and will go right back to work putting out boost.

Without this by-pass valve feature the compressor/turbine wheels tend to stall between shifts and it takes longer to build up boost again after each shift. This is also true when the throttle is lifted in a corner for any reason. When you get back in to the gas, the by-pass valve actually is slow in closing and lets the turbine free wheel for an eye blink, bringing the boost on much quicker. Why any driver would spend money and give this throttle response advantage in away for the sake of noise of a blow-off valve is almost funny to think about. Yet, many shops will sell you a blow-off valve with a straight face. But, now you know. This is a classic case of, 'If it ain't broke, don't fix it".
 
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