"The BIG BOV thread" (Where all bov question threads get merged) - Page 311

This is a discussion on "The BIG BOV thread" (Where all bov question threads get merged) within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; what do you do about the tube that normally runs from the BOV back to the intake?...

  1. #4651
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    For those of you with aftermarket BOV

    what do you do about the tube that normally runs from the BOV back to the intake?
    It is better to have others think that you are a fool than to open your mouth and remove all doubt


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  3. #4652
    Registered User Wrinkleboi's Avatar
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    if the bov doesnt recirculate, then you need to plug the recirc tube. you're car will run like crap if you dont seal off the tube.
    all blow off valves should come with a plug for this, but if they dont you can go to home depot and get a 1 3/8" white rubber sink drain plug for $1.39 plus tax and it works like a charm .
    bryan

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  4. #4653
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    is there any truth to the rumor that a fully vented BOV on a stock car can actually hurt performance or in some way damage the engine?
    It is better to have others think that you are a fool than to open your mouth and remove all doubt


    02 WRX 44k - sold 2/28/5
    96 Corolla 128k
    92 Corolla 160k
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  5. #4654
    Registered User hellafastWRX's Avatar
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    Quote Originally Posted by Wrinkleboi
    if the bov doesnt recirculate, then you need to plug the recirc tube. you're car will run like crap if you dont seal off the tube.
    all blow off valves should come with a plug for this, but if they dont you can go to home depot and get a 1 3/8" white rubber sink drain plug for $1.39 plus tax and it works like a charm .
    bryan

    Good improv idea. Do you have the chain attached to it to?
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  6. #4655
    Registered User hellafastWRX's Avatar
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    Quote Originally Posted by JeremyL
    is there any truth to the rumor that a fully vented BOV on a stock car can actually hurt performance or in some way damage the engine?

    Over time the rich conditions will break down the cat in the uppipe. This will send pieces of metal into your turbo. = very very bad. Get a catless uppipe just to be safe but you dont have to worry about that for a while .

    Enjoy the bov. I like to scare people jogging with mine.
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  7. #4656
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    is that the only thing to really worry about? why would a BOV make the car run rich?
    It is better to have others think that you are a fool than to open your mouth and remove all doubt


    02 WRX 44k - sold 2/28/5
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  8. #4657
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    well it just makes the car rich in between shifts, because thats the time it is releasing air into the atmosphere that would normally be recirculated into the intake and then into the engine. basically every time the bov is releasing, your engine is getting a little less air than it expects, so it throws the AFR off a bit. the only difference i notice is a little afterfire now and then. if you have a straight through exhaust without any restrictions you may find that you're shooting flames too because of this
    bryan

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  9. #4658
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    could any type of reflash or tuning cure that? so what kind of effect could that have on the longevity of the motor?
    It is better to have others think that you are a fool than to open your mouth and remove all doubt


    02 WRX 44k - sold 2/28/5
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  10. #4659
    Registered User Wrinkleboi's Avatar
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    well i'm certainly not the final word when it comes to technical engine questions, but in my understanding it wont really have a negative affect on your engine's well-being, but it may slow you down .1 in the 1/4 mile.
    bryan

    -2003 Blue WRX, complete 2007 STi Engine/Drivetrain transplant - Pic 1 | Pic 2 | Pic 3 | Pic 4 (new!)
    -1994 Black Supra TT 6MT - Pic | Build/Restoration Thread: 67mm, Fuel, Painted Engine Bay, Fuse Box Relocation, Wire Tuck, etc.

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  11. #4660
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    Hey Jeremy,
    I'm pretty sure it's just like the situation on our MR2's. (I'm archiemr2 on mr2oc)

    Because the WRX has an AFM, let's say that "A" amount of fuel goes into the car. The AFM puts "F" amount of fuel in the mixture because the ECU has looked in its electronic tables how much fuel to put into the mixture when you have "A" amount of air.

    Well, when you vent your BOV to atmosphere instead of back into the system, you lose "x" amount of air to the outside world. You no longer have "A" amount of air in your motor...you have "A" - "x" air in your motor. Yet...the ECU doesn't know that you lost some air and still thinks you have "A" amount of air in your motor, so it's putting in enough fuel for "A" amount of air...not "A" - "x" amount of air. So you've got too much fuel, and it runs rich.

    It's only doing this abnormally when the BOV is open...ie between shifts if you're revving the car hard. There aren't really too many adverse affects on our MR2's for this...the biggest things are less smoothness betweeen shifts and with a downpipe and open exhaust you might make fire. Apparently on the WRX there is a cat in the up pipe. I'm not sure if the rich condition like hellafastWRX said will actually break down the cat faster or not. Seems more like a theory to me. Please feel free to give more info on that one.

    But overall, that's why you run rich with a BOV vented to atmosphere and in general the effect is just slightly less smooth transition between shifts. Does running rich damage the motor? Not at all. But if there are side effects like pieces of the cat going into the turbo...then that's not good. I'm still not sure whether that idea has any merit to it yet or not though.

    HTH

  12. #4661
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    Oh, and I'm not sure about a reflash, but..

    You can supposably tune to compensate for it with devices like the S-AFC. I could never seem to figure it out with mine when I had it.

    If you run a standalone EMS, you can remove the AFM altogether since the EMS will measure the air volume with a temperature sensor and a MAP sensor instead. These sensors monitor the air after the intercooler so it doesn't matter if you're throwing air out before it gets there. So with an EMS, you also won't have the rich condition problem when shifting with a BOV vented to atmosphere.

  13. #4662
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    Quote Originally Posted by MiStiC NiNja
    worx says 50% for daily driving should workout fine (at least for my WRX) might be different for the STi, but def. don't DD w/ 100% you'll fry your cats.

    it says 50/50 in the directions. thats what i currently have it set on. drives fine.
    05 Black STi

  14. #4663
    Registered User MiStiC NiNja's Avatar
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    Quote Originally Posted by 5spdfrk
    Unless you dont have any cats!
    hahaha! do you ever shoot off an occasional fireball?

  15. #4664
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    what about a 50/50 BOV ? would you just cut the rich between shifts condition in half? if its only in between shifts when youre boosting hard i mean that doesnt make up very much of your driving time. we had a used STi on our lot that had an aftermarket BOV and while it was kinda annoying (and i know im gonna get flamed for it) but it sounded really cool
    It is better to have others think that you are a fool than to open your mouth and remove all doubt


    02 WRX 44k - sold 2/28/5
    96 Corolla 128k
    92 Corolla 160k
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  16. #4665
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    Quote Originally Posted by MiStiC NiNja
    hahaha! do you ever shoot off an occasional fireball?
    I hope so! I dont know for sure because no one I know has ever been behind me. I do get afterfire a lot and when it happens the people behind me back off, so I dont know if it is because of the sound, the fireball, or both!
    '02 WRB WRX
    '92 Civic Si

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