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What's the go with these turbo car BOV's ?

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  • What's the go with these turbo car BOV's ?

    The other night I rode along Leach highway at a nice easy pace and there was a couple of guys in a WRX keeping pace for a few sets of lights.

    The driver was taking it easy, using just a light throttle and wouldn't have gone over about 2500rpm I s'pose.
    His blow off valve must have been set for like 1psi or something because every time he changed gears, the thing gave a loud PSHHHH !

    Now I know these guys do it because they think the noise is cool, but my question is...

    If the blow off valve is set at a very low pressure like this one obviously was, doesn't that mean that when you put the boot into it that it will lose boost pressure as the BOV will open and bleed some/all your boost off ?
    Or am I missing something here?
    CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

  • #2
    Not a turbo wizard, but as long as the throttle is open, there's effectively no pressure on the show off valve. When you back off, pressure builds up and busts it open for the lay-deez.

    People that actually know what they're talking about, please correct me, I am very likely completely wrong on this one.
    such comment
    wow
    many post

    Comment


    • #3
      Rocket: when under boost and with the throttle body open, the boost pressure actually helps keep the BOV closed.

      The opening is caused by the pressure differential between your intercooler piping and inlet manifold (after t/b - the BOV runs a vacuum line to your inlet manifold for this purpose).




      If the pressure *difference* between the inlet manifold and the cooler piping is greater than the spring tension, it will go off... when you close the throttle under boost, the inlet manifold pressure goes to vacuum, the cooler piping is still pressurized... hence... bov...


      Really, you just need enough spring tension to take into account pressure drop between where your BOV is mounted (often on the hot side of the cooler plumbing), and your inlet manifold (so it stays closed with the throttle open or partially open) - any more spring tension is a waste....
      Last edited by thro; 30-12-2007, 10:50 PM.
      “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

      Comment


      • #4
        WRX owners Rocket, you summed it up.

        It was probably a GFB, or Turbosmart one, they are designed to flow as much as a Maccas straw, but they have a 12" fuel funnel off the end so people three streets away know its a turbo.

        Some call it "bling", i call it "i am gay".

        Anyways, can they if set too low, yes and they do. But soon as he hits full vac it will open, as i said the reason you heard it so loudly cause of probable design. I run the big GReddy Type R units, because they flow, and they are a valve, not piston design like the cheaper ones, and will not open unless there is a good amount of boost on de-cell.

        Comment


        • #5
          *EDIT* question answered by people who know shit.



          Well that's the thing Cam, BOV's are there for the safety of your engine.
          From what I understand, you only really need them when running high boost as when you shut the throttle as the engine is boosting, the pressure waves reverse back to the turbo compressor wheel and try to stop it spinning. At high boost, it apparently can break a shaft.
          But a lot of guys set the BOV at low psi so they get the noise to impress the chicks at the milkbar.

          But surely shutting the throttle and building pressure in the link pipe from turbo to throttle body is the same as building boost in the link pipe.
          So to my thinking, if you've got your BOV set at 8psi and your waste gate set at 10psi, then surely the BOV will relieve pressure before you get to full boost.

          Where's Thro when I need him ?
          CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

          Comment


          • #6
            ^^ see my above post

            Your wastegate will stop the turbo building more pressure, but it won't release the pressure that's already there.


            As far as BOVs being "needed", well that's open to debate. I haven't seen/heard of anyone (first hand) who's killed a turbo from not running one.

            As I understand it, they're more about keeping the turbo spooled up - rather than the compressor wheel stalling and trying to pressurize a closed system, the BOV just vents so that it can work with less resistance until you open the throttle again...


            Again... as I understand it....


            edit:
            To clarify... you don't generally control boost with a BOV. You don't set one to X psi and that's when it opens... you can set the spring pressure to say 4psi (just for the sake of example), and run 25 psi of boost - while the throttle body is open, you'll have 25psi in the inlet manifold and ~25psi (+ pressure drop through the cooler /open throttle of X psi) in the cooler pipes ... if the difference between the 2 areas is less than 4 psi (which it most likely will be when the throttle is open) then the BOV will stay shut...

            As to bovs... i have a sard R2D2...which I think needs adjusting
            Last edited by thro; 30-12-2007, 11:04 PM.
            “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

            Comment


            • #7
              Originally posted by Foofie Foofie View Post

              Some call it "bling", i call it "i am gay".
              Yes Saf, yes indeed.
              CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

              Comment


              • #8
                Originally posted by thro View Post
                As far as BOVs being "needed", well that's open to debate. I haven't seen/heard of anyone (first hand) who's killed a turbo from not running one.

                As I understand it, they're more about keeping the turbo spooled up - rather than the compressor wheel stalling and trying to pressurize a closed system, the BOV just vents so that it can work with less resistance until you open the throttle again...
                Thro, Nissan rear wheels fall off , the ceramic ones that are glued on .... this is common from the twist, and i know for a fact with higher boost Toyota's CT20's that run on the 3S-GTE like to snap as they made a thin shaft to avoid lag. When it grenades it kills the WHOLE engine

                As far as the spooled up part, its a gimmick they sell em for. At motorplex i have run 2 customers cars, consistent cars, with and blocked ... no diff.

                I only use them for safety.

                I do like the turbo surge / chatter tho ... driving my 180 in Euro couple weeks ago, makes such a glorious sound when your givin it some and then changing up a gear.

                Comment


                • #9
                  Originally posted by Foofie Foofie View Post
                  I do like the turbo surge / chatter tho ...
                  My bike does this, it makes my pants tight every time.
                  It's one of the reasons I wouldn't fit a BOV to it.
                  That and the fact that I don't want people to think I'm a WRX :mellow:

                  I didn't know the BOV was tied to inlet manifold pressure after the T/B. That makes sense.
                  CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

                  Comment


                  • #10
                    No mate before the TB. It goes in the tract between the turbo and the TB.

                    I hear you on the pants thing !. It always reminds me of the high HP JDM D1 cars .... as they get on and off around a corner .... sounds so so sexy.

                    Comment


                    • #11
                      Fair enough, i thought the skyline ceramic turbo failure thing was due to simple overboosting.

                      To be honest i noticed no difference with BOV or none when I had none for a while *shrug*.

                      To highlight what i mean about the two pressure areas, I just drew a schematic





                      edit:
                      the bov uses pressure from both before AND after the throttle body. the vacuum line runs to the inlet manifold after the t/b (this is what helps keep it closed under boost with open throttle), but it vents pressure that is trapped before it....


                      I still get chatter or "flutter" on teh cage a bit if i'm not really hurting it, even with the BOV. Was quite funny when I had no BOV for a while actually... the cops pulled me over and were looking for the BOV... i'm like "it doesn't have one, that's flutter". They didn't know what I was talking about. Then again, they pointed at my strut brace and asked what that was, so no surprises there...
                      Last edited by thro; 30-12-2007, 11:25 PM.
                      “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

                      Comment


                      • #12
                        Originally posted by Foofie Foofie View Post
                        No mate before the TB. It goes in the tract between the turbo and the TB.

                        high HP JDM D1 cars ....
                        Yeah Saf, I was referring to the vacuum line to the inlet manifold as per Thro's drawing.

                        I have no idea what a JDM D1 is but I always think of rally cars when they are getting on and off the throttle.
                        CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

                        Comment


                        • #13
                          Fave D1GP car

                          [ame="http://www.youtube.com/watch?v=PxDmIkqR4M0"]YouTube - Ken Nomura drifting 4th gear in his Blitz Uras ER34 Skyline[/ame]


                          edit:
                          If you've only seen the aussie drifting scene... the japs have guys over there who actually know how to do it
                          “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

                          Comment


                          • #14
                            Ahhhh D1 ! Now I know what you mean.

                            Cool vid !!

                            I want to ride my bike now, but it's dark and I need the headlight pointing at the ground
                            CAUTION: ATTEMPTING TO OVERTAKE THIS VEHICLE MAY RESULT IN A HIGH SPEED WHEELIE

                            Comment


                            • #15
                              Another vid with more smoke, more power... angry supra

                              [ame=http://www.youtube.com/watch?v=jpPKL80XUYg]YouTube - JUN Supra Famous Drift[/ame]
                              “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

                              Comment

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