"The BIG BOV thread" (Where all bov question threads get merged) - Page 50
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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; At the expense of sounding like a real idiot and being too lazy to read the other threads, I have ...

  1. #736
    Registered User phast's Avatar
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    yet another mbc question.. likely undiscussed

    At the expense of sounding like a real idiot and being too lazy to read the other threads, I have an MBC problem.

    I have been using an MBC similar in build and operation to the Joe P and Hallman for several years on two different cars. It has served me well on the WRX thus far.

    Tonite, I installed a rather largish Garrett turbo and the boost controller doesn't seem to agree much with it. No matter how much I cranked down on the spring, I couldn't get more than wastegate boost or maybe a couple pounds over that. I pulled the hose off the WG actuator and voila, boost for days.

    It's worth noting that I had to use a larger hose from the compressor outlet to the inlet of the MBC in order to accomodate the larger nipple on the compressor. Is this the cause for not making any boost?

    Any ideas?
    -jay
    i drive a jeep n stuff.

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  3. #737
    Registered User is2scooby's Avatar
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    I'm running a VDO guage and gauge cup and have received many comments on it's stock-appearing good looks. It's very functional, not *bling bling* at all (which I didn't want) and was around $65 total from www.summitracing.com
    Aloha, Richard...
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  4. #738
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    mmmm, garrett turbo...

    sorry, back to reality. my answer is "i have no clue" but you get a bump.

  5. #739
    Registered User thechickencow's Avatar
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    Can't your link control boost? I would think that running a bigger turbo would mean that you want to spend more than ~$50 on a boost controller.

    But...I don't have an answer either.

    Jay

  6. #740
    Registered User bcblues's Avatar
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    My guess is that the MBC itself is the bottleneck. The MBC internal circuits probably will not flow enough air to allow the WG to operate freely. Just a guess. It could also be the remainder of the tubing creating a flow restriction on the opposite side of the MBC. Try running the same size tubing on both sides first. If that fails, you may need a different MBC?? What brand MBC are you running?

  7. #741
    tan
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    Thinking Man's Engine tan's Avatar
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    Pssch.....Pssch.....Pssch.....Pssch

    it makes a cool sound though, when you vent it to the atmosphere.

  8. #742
    Registered User VetteVert's Avatar
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    The original hose off of the compressor outlet has a restrictor in it. This restrictor is very small. I know for a fact that the stock turbo won't boost worth diddly without the restrictor in place. See if it will fit the new hose, or make a new restrictor. The hole is merely a pinhole...very small.

    VV

  9. #743
    Registered User JTREX's Avatar
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    Originally posted by tan
    Pssch.....Pssch.....Pssch.....Pssch

    it makes a cool sound though, when you vent it to the atmosphere.
    I vent to atmosphere after to much mexican, does that make it a cool sound as well?
    Drag racing? I like my racing to last longer than the average orgasm...

  10. #744
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    pssh pssh pssh... sounds more like some kind of subaru-water-torture to me.

    jb

  11. #745
    Registered User phast's Avatar
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    Originally posted by bcblues
    My guess is that the MBC itself is the bottleneck. The MBC internal circuits probably will not flow enough air to allow the WG to operate freely. Just a guess. It could also be the remainder of the tubing creating a flow restriction on the opposite side of the MBC. Try running the same size tubing on both sides first. If that fails, you may need a different MBC?? What brand MBC are you running?
    That's the thing though. There is obviously plenty of "signal" getting thru the valve to the wastegate. I doubt the valve is a restriction. The MBC was purchased from http://www.ffwdconnection.com.


    posted by VV
    The original hose off of the compressor outlet has a restrictor in it. This restrictor is very small. I know for a fact that the stock turbo won't boost worth diddly without the restrictor in place. See if it will fit the new hose, or make a new restrictor. The hole is merely a pinhole...very small.
    I haven't used any of the stock boost control hoses since the 2nd week I had my car. This MBC went on and all the stock boost control hoses and solenoid came out.

    After churning through this in my head all night, I wonder if the extra hose volume, might be too much for the hose on the other side. When the valve opens, all that air is stuffed into a tinier volume and more pressure is seen on the wg actuator causing it to open early. Sound feasible?

    I'm also going to try and get a pressure source from the intake manifold instead of the compressore housing and see what happens.
    -jay
    i drive a jeep n stuff.

  12. #746
    Registered User pace's Avatar
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    Re: yet another mbc question.. likely undiscussed

    Originally posted by phast

    ..
    Tonite, I installed a rather largish Garrett turbo
    ..
    *Cough* *cough* understatement of the 21st century.

    On topic: Weird! From your description it seems that your MBC cannot be adjusted to an entirely 'closed' position? Since that should have the same effect as disconnecting the WG signal hose entirely.

    The only thought that came to mind was to ask what the WG spring is rated at. If it's real light duty then I guess it's feasible that your MBC cannot be 'tightened' down enough to allow a small enough signal. Beyond that; yes definitely try matching the hose ID as it would seem possible that could cause problems. If that fails, you could always try one of the hose restrictors that the stock setup uses.

    Good luck.

    -Pace

  13. #747
    Registered User phast's Avatar
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    Update.. I tore the damn thing apart this afternoon, cleaned it, and low and behold it works again. Guess the ball must have gotten stuck in there somehow.
    -jay
    i drive a jeep n stuff.

  14. #748
    Registered User Quantum-Racing.com's Avatar
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    I didn't get any photo instructions other than a schematic (I bought the universal). Usually you just loosen the screw until you feel it isn't pushing against the diaphragm and then turn the car on and tighten it back down until you don't feel any air at idle sucking in.
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  15. #749
    Registered User WRXin''s Avatar
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    Re: Installing Blitz DD BOV...

    BozzWRX -- Let me know how it sounds...I love BOV's. BTW the Blitz is a 100% atmosphere, right?
    Fahd

    Floats like a butterfly and stings like when I pee!

  16. #750
    Moderator TypeC's Avatar
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    Originally posted by bcblues
    My guess is that the MBC itself is the bottleneck. The MBC internal circuits probably will not flow enough air to allow the WG to operate freely. Just a guess. It could also be the remainder of the tubing creating a flow restriction on the opposite side of the MBC. Try running the same size tubing on both sides first. If that fails, you may need a different MBC?? What brand MBC are you running?
    It works the other way around. If the mbc can't flow enough to send the boost signal to the WG you'll overboost.

    I too had this problem (underboosting). I installed a VF turbo, put in the mbc and it wouldn't get more than wg pressure (even at the setting for 17psi for stock turbo). I swapped my AVC-R in and it works fine. It really annoyed the hell out of me. I never figured it out, just let it be.
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