The Mystery of the Eager BOV!

Discussion in 'The Garage' started by mcglsr2, May 5, 2015.

  1. mcglsr2

    mcglsr2 Well-Known Member SN95 Supporter

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    Zoinks! Alright, I have a mystery for you guys. Let's see if you can solve it! (By the way, I don't know the answer!)

    The Story:

    I was at the gas station the other night, filling up my Fiance's car. There was a car at the pump next to me, A VW. Maybe a Jetta? Not sure. It had rims, painted brake calipers (red) and was lowered. When the owner got in the car and started up, I immediately heard the characteristic "ppssshhh" of a BOV - in this case quite loud. He then drives away, going pretty slow, maybe like 10 feet, and then a very loud "psssshhhhhh" - either he shifted or let of the gas to slow down in the parking lot. As he drove out of the parking lot, again going slow, I heard a couple more loud sound-offs from the BOV.

    And The Mystery:

    Alright. So the question is: how in the world was his BOV sounding off? I've got a gen 1 Mistu BOV on one of my cars (and a stock STI BPV on the...STI). I'm pretty versed in how turbos work, the concepts and practical applications. The point of a BOV is to release pressure in the pipes when the throttle body closes, in theory (and in real-life, for the most part) in an effort to prevent pressure backing up against the compressor. For it to function, it must have pressure in the pipes - as in the turbo is producing boost. Atmosphere does not count as pressure, as the outside air is at atmosphere. Sooooo. The BOV should not sound while under vacuum or at atmosphere. And in my experience, the loudness is often driven by the amount of pressure being vented.

    So. How was his BOV doing that? Was it fake? Was it designed specifically to make noise (and how, assuming it has to use built-up pressure)? It's not very likely that as he was slowly leaving the lot he was building up boost. Unless his timing was wicked retarded or something? Someone, solve this mystery!
     
  2. Wichers123

    Wichers123 Well-Known Member

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    Vw's and srt4 are bad about that. So let me explain. They use a small turbo with small piping that it in fact creates pressure along with a small bov/dv the rush of air coming out sounds like something wild. The bigger the bov/dv the less you hear it unless you are using a huge turbo that creates a lot of cfm's
     
  3. duh09

    duh09 Legend

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    My buddy's A3 with the 2.0L turbo was the exact same way with an aftermarket diverter valve. If it made ANY boost (2-3psi) it would make noise when letting off. Kinda cool, mostly annoying just because of how he drove just to make it CONSTANTLY make noise. Ended up causing a lot of issues with it running right and he took it off.

    My SRT4 would build boost quick enough to be able to make SOME noise but not very much just putting around, had to be giving it a little more than usual to get it to psh at a gas station.
     
  4. torch318

    torch318 Active Member

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    He could of been running a procharger big red race valve instead of a bov.
     
  5. JerZeyStangz

    JerZeyStangz Well-Known Member

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    I agree with all the comments because I own a 01 Audi A4 1.8T, the turbo is small and it doesn't take much to make it vent to atmosphere. Fortunately my Forge Diverter valve on my car doesn't make any noise which I like that previous owner put on.
     
  6. rz5.0

    rz5.0 Legend

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    Very soft spring on the bov..