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  • Blow off operation

    hi.im just wondering how is our OE blow off valves operating?
    i mean,is the boos forcing the valve shut and then with foot off the throttle,vacuum will lift valve open or can the boost overcome the spring tension and force the valve open causing unwanted boost level drop (for example if the valve is 22years old :-)

  • #2
    First off we have by-pass or recirculation valves, not blow-off valves.

    Read this: By-pass valve info:

    http://forums.quattroworld.com/s4s6/msgs/20994.phtml

    RS2'd 93 UrS4 5 spd sedan
    94 UrS4 V8 6 spd manual avant

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    • #3
      Sorry-I ment recirculation valve
      so it looks like pressure from Turbo could actually work against weak spring causing problems .
      i wonder if people with 400+BHP are fitting upgrated valves?

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      • #4
        Use the one for 225 HP AUDI TT MK1 , it is OEM with the hardest spring, and holds 1.9 bar no problem , should last a few years . I am considering the Forge recirc Valve with vent to atmoshpere option , but the cost is ....

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        • #5
          Originally posted by Cordoba16vt View Post
          Use the one for 225 HP AUDI TT MK1 , it is OEM with the hardest spring, and holds 1.9 bar no problem , should last a few years . I am considering the Forge recirc Valve with vent to atmoshpere option , but the cost is ....
          Good info buddy.If you will fit the one that is venting to atmosphere you will have to move MAF isn't it?

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          • #6
            I use Forge type get a nice little woosh on gear changes and doesn't affect the air maf situation as far as I know

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            • #7
              If you think about it, the boost pressure is present on both sides of the diaphragm. The spring is just strong enough to hold it shut when idling.

              S2 Coupe 3B Project


              Ur quattro restoration

              S2 Avant

              Boost is the new rock and roll!
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              • #8
                Originally posted by piotr View Post
                Sorry-I ment recirculation valve
                so it looks like pressure from Turbo could actually work against weak spring causing problems .
                i wonder if people with 400+BHP are fitting upgrated valves?
                If the valve is installed correctly, when on boost the boost pressure acts against the side of the sprung part of the valve so it's not being forced open. Boost pressure also acts on the vacuum nipple which is holding the valve shut. If the valve is installed the wrong way around (very easy to do) the boost pressure acts against the diaphragm forcing the valve open at higher boost levels. The diaphragm is a point of failure and the valve is easily tested. Once removed push on the spring and before releasing it put a finger/thumb over the nipple. It should hold vacuum when you release the spring. If not the diaphragm may be leaking. You can also blow on the boost side of the valve (pipe at 90 degrees to the diaphragm) and it should be sealed. If it leaks (i.e. you can get some air through) then it's no good. I use the 710N OE valves in my cars and they are reliable. My RS4 is at around 440hp on 21psi of boost pressure.

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                • #9
                  Hi guys,so I tested the valve like Le Mans advised and it turned to be faulty,Looks like it was leaking.I have installed the new one (genuine stock one)and the problem is fixed
                  This thing is flying now.Also noticed that it sounds different.Before it was more like flattering sound on the gear change,now it sounds like blow off.Anyway-thank you boys for your input

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                  • #10

                    S2 Coupe 3B Project


                    Ur quattro restoration

                    S2 Avant

                    Boost is the new rock and roll!
                    sigpic

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