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Internal wastegate spring pressure

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    Internal wastegate spring pressure

    I've been working on my s15 with efr7163 turbo and have for a long time been plagued with boost holding issues.
    I ended up going with a 4 port mac valve and have 22psi of springs in the gate and it seems to hold around 24-26psi ok with the EBC.
    The thing I find strange is with the EBC off, It only seems to pull 13psi of boost in 3rd gear.
    Am I not loading up the car enough (need a dyno) to get more boost or am I really seeing a pressure differential of about 9 psi ?
    I always thought the wastegate spring pressure is what you should roughly see with EBC off.
    Learned folk, please learn me up.

    #2
    how much preload do you have on the actuator?

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      #3
      I've put in 2 turns as per the Turbosmart manual. If I put more it will take more boost before blowing open, but for some reason they really stress the point in the manual that its 2 turns.

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        #4
        Unfortunately (and also fortunately) EFR's have a large well designed internal gate that flows very well.

        The large diameter of the gate flapper is influenced by the exhaust back pressure with the small A/R turbine housing and the low waste gate actuator to gate head diameter ratio means that a higher than normal spring pressure is needed, and causes the boost to drop off with increased RPM and back pressure.

        I have the same turbo on a 1JZ and have the same issue. I have changed to the the dual port turbosmart IWG-75 and a 4 port MAC valve and it was holding boost pressure. It is very sensitive though.

        I'd like to try a electronic actuator like on the VW's and Audi's, or one of the new electronic gates from Turbosmart.

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          #5
          Originally posted by the big fist View Post
          I've put in 2 turns as per the Turbosmart manual. If I put more it will take more boost before blowing open, but for some reason they really stress the point in the manual that its 2 turns.
          Any more than two turns effectively shortens the stroke of the actuator, so you reduce the ability to flow as much through the gate. It will increase the cracking point of the gate, but it will still drop with RPM and back pressure.

          Essentially the 38mm gate head has 9psi worth of force (exhaust gas) trying to push it open and a 22psi spring trying to close it and you end up with 13psi.
          Last edited by taijohnsen; 10-11-19, 08:48 PM.

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            #6
            Thanks taijohnsen.
            The turbo comes on pretty hard when I have enough preload wound in to stop the boost drop.
            Ideally I would like to run around the 18 to 26psi (gear selected) range and am thinking of dropping the springs back to a lower pressure and trying to control with the 4 port.
            Do you think that is worthwhile or stick with the 22psi springs to battle the back pressure ?
            Cheers,

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              #7
              The twin port IWG-75 is a bit leaky on the bottom port when compared to an external gate, I think they have a new one which has a ball joint to allow for the gate arm to swing without moving the shaft out of the bottom of the actuator to get a better seal (more authority)

              What I plan on doing is dropping the the spring pressure (boost per gear also) and see if the 4 port can hold the desired boost. Ideally a well setup closed loop too.

              With is the way is was before (essentially that same spring pressure as you) very small % difference in duty cycle would cause over boost and it would just chase it's tail.

              Hopefully this will make it a bit more controllable. I dropped the frequency of the solenoid to get a bit more range too.

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