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RS2 turbo wastegate control

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  • RS2 turbo wastegate control

    A couple of mechanics (not Audi experts) have commented to me recently that they are surprised that the watsegate is not pressure controlled via the hose connector as standard. I am running a hybrid K26/27 turbo with 1.9 bar wastegate spring. I wonder if anyone has experience of controlling the wastegate by pressure feedback rather than by a preset spring?
    Cheers
    Don
    ---------------------
    Everything in perfect working order

  • #2
    That Does not sound right..... you can use a manual boost controller over the WFV but generally not recommended on AudiĀ“s as you lose all your safeties controls....
    RS 2 580HP

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    • #3
      All S2 and RS2 are controlled by pressure feedback N75 valve as standard with only a small spring in the wastgate, about 8 psi if I recall.

      A stiffer spring might be required when running higher boost to prevent oscillations but 1.9 bar seems extreme.

      I run a 1.3 bar spring then use the boost frequency valve to take the pressure up to 2 bar.


      Sent from my D5803 using Tapatalk


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      • #4
        1.9 bar absolute or 1.9 bar gauge pressure?
        Panthero CoupƩ quattro 20vt
        Indigo ABY coupƩ
        Imola B6 S4 Avant

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        • #5
          Survey says... X

          ā€‹ā€‹ā€‹ā€‹ā€‹ā€‹What boost does the car run? Does it have a wastegate frequency valve connected to the underside of the wastegate via a hose, which relays pressure...

          Top nipple is not connected as standard.

          ā€‹ā€‹ā€‹ā€‹ā€‹
          Cheers'en, AndyC
          1994 ABY Coupe - Projekt Alpinweiss

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          • #6
            I dont want to hijack the thread, but can someone tell me whats the stock depth of the ABY wastegate screw ?

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            • #7
              As standard, the ECU controls boost to above the waste gate spring pressure by bleeding off air from the lower chamber via the N75 valve. If you are running a 1.9 bar spring without any hose connections then there is no way the ECU can control the boost pressure so it will regulate to the spring preload (1.9 bar). I'm not very good at explaining it, but I found this document very helpful: Boost Control Rev3

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              • #8
                8 turns from flush which is approx 10mm deep. HTH
                Cheers'en, AndyC
                1994 ABY Coupe - Projekt Alpinweiss

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                • #9
                  Basically, the wastegate is a fail UNSAFE design, so even a stock spring can produce enough preload on the wastegate valve to cause over 2 bar of boost. Take the small bore feed off the WG if you don't believe me

                  The pressure from the inlet acts AGAINST the spring preload, so as boost builds, there comes a point where the pressure on the diaphragm results in a force that is equally to or greater than the spring preload. I would call this the 'crack pressure' and this is what is referred to by 1.9 bar above and 0.4 Bar in the case of the stock spring.

                  The reasons for a higher spring preload are response and to prevent creep under high exhaust manifold pressure, where the stock spring isn't manly enough.

                  By diverting boost in some proportion to the inlet and WG, the N75 valve controls the pressure in the lower chamber such that the valve opening distance is controlled and thus turbine speed and thus boost reaches a desired value.

                  If your car only boosts 1.9 Bar absolute (0.9 gauge), then the N75 isn't bleeding any boost; conversely, if you're running more boost, then you have pressure controlled boost.

                  Simply, to prove the point, disconnect the N75 and see what boost you have on both situations.
                  Last edited by Rusty; 20 August 2017, 23:55.
                  Cheers'en, AndyC
                  1994 ABY Coupe - Projekt Alpinweiss

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                  • #10
                    I'm trying to get my head around how this all works at the moment (think my turbo died) but are you saying disconecting n75 or the small feed it has to the wg will leave the turbo constantly spinning with stock spring but make it pressure controlled with the bigger spring above?

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                    • #11
                      The original poster might want to read this:

                      N75 Wastegate Frequency Valve (WGFV) location, function and PN info:

                      http://forums.quattroworld.com/s4s6/msgs/20987.phtml





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

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