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Help tuning out boost spike - Subaru WRX - External WG with three port solenoid

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  • Help tuning out boost spike - Subaru WRX - External WG with three port solenoid

    I am having issue with boost control with my Autronic SM4 powered WRX. This is not my first build, I've been running the Autronic for years but this is the first time I have swapped over to using the Autronic boost controller. I will be honest, after 6 hours on the dyno I cannot tune out this boost spike. I either seem to have a boost spike then great flat boost or no spike and boot hunting, as in wavy boost with as much as 4-5 psi difference. this is a track car so it sees a lot of 5th/6th gear long pulls so boost spikes and hunting is bad.

    I have inserted my CAL file and a log from one of the dyno sessions.

    I'd love some input and help.

    I have played with almost everything (including HZ) and nothing seems to dial in the boost. I will say that other than the spike the control is great.

    WG boost (mechanical) is ~15 psi

    WG is attached to a three port boost control solenoid, see picture.

    I know boost control is somewhat working as I can see the solenoid duty cycle doing it's thing. What I cannot do is setup setting that either remove the spike or result in wavy boost hunting.

    I'd really like to understand the relationship between the setting.

    Spike seems to get bigger with the greater boost range. However too low of a setting on boost range results in hunting

    Dynamic comp, high seems to result in wavy boost hunting but no spike. Seems counter intuitive.

    Offset works as expected.

    No modifier set.

    I've tried 20Hz for OP control and the boost hunts like crazy.

    I see similar results in the track.

    I'd love some pointers. I kind exhausted my understanding. thanks - Mick

    Attached Files

  • #2
    I would try the following; Boost Range = 150kpa (you might need to adjust the Offset after this), Dynamic comp = 10.

    I would also make the hose connections slightly different to the diagram. Feed the solenoid and wastegate bottom from different pressure sources. The wastegate bottom can be fed from the compressor cover but try to feed the solenoid from pressure after the intercooler (so the o-ring in the solenoid gets somewhat cooler air flowing over it). Having different pressure sources means the solenoid can't bleed any air from the hose which would otherwise be pressurising the opening side of the wastegate.

    I would have also thought 20Hz should have been reasonable. As the engine does not seem to have variable cam timing you could maybe also try connecting to one of the hardware PWM cam outputs (they will have different flyback voltage circuitry so might control the solenoid better).
    Last edited by Ian; September 12th, 2017, 12:16 PM. Reason: Edit, to put the line spacing back in

    Comment


    • #3
      Seems weird that you are seeing a larger spike with higher boost range, that`s usually the other way around.
      If i where to try and fix this, i would start with a really high range ( something like 230,) and about 8-10 in dynamic comp.
      My guess is that the spike should be smaller then.
      And when you get it ironed out, i would decrease boost range as much as you could before the spike came back ( for a more aggressive boost rampe)

      Comment


      • #4
        Originally posted by Ian View Post
        I would try the following; Boost Range = 150kpa (you might need to adjust the Offset after this), Dynamic comp = 10.

        I would also make the hose connections slightly different to the diagram. Feed the solenoid and wastegate bottom from different pressure sources. The wastegate bottom can be fed from the compressor cover but try to feed the solenoid from pressure after the intercooler (so the o-ring in the solenoid gets somewhat cooler air flowing over it). Having different pressure sources means the solenoid can't bleed any air from the hose which would otherwise be pressurising the opening side of the wastegate.

        I would have also thought 20Hz should have been reasonable. As the engine does not seem to have variable cam timing you could maybe also try connecting to one of the hardware PWM cam outputs (they will have different flyback voltage circuitry so might control the solenoid better).
        I'll try this on Thursday at my track day.

        It's clear though that I don't understand Boost Range or the effect the Dynamic Comp has. Would you mind explaining what these variables do exactly?

        Thanks!

        Comment


        • #5
          The Boost Range is (approximately) telling the ECU how much authority the wastegate / turbo combination has. Imagine the two extremities of control, 0% and 100% applied to the solenoid. In the case of 0% you will get wastegate pressure while 100% will get you how much boost the wastegate / turbo is capable of (allowing for things like exhaust back pressure and the side connection operating on the wastgate to open it, and the top connection and the spring trying to close it). In reality, the solenoid flow won't be linear near the 0% or 100% duty cycles and the turbo doesn't have equal efficiency across its operating range, and you are probably not after the absolute maximum flow of the turbo.

          A range of 150 kpa is telling the ECU that the combo is capable of about another 150kpa of boost on top of the wastegate spring pressure. If you under-do the range then the ECU (in the open loop component of the control) will most likely overshoot the target (because it is anticipating that the turbo cannot make as much boost as it really can and so will apply too much duty cycle to the solenoid). Similarly, the Dynamic Comp is telling the ECU how agressively to chase the target. Too much and it will overshoot the target if increasing boost and undershoot if decreasing boost.

          Comment


          • #6
            Great. Thanks. At track now going to test and tune

            Comment


            • #7
              Hi. For some reason I cannot upload my track dat .DAT files, the forum upload says they are too large. I'll have to explain the results.

              My first session using the post dyno CAL file settings, 110 Boost Range and 15 as dynamic comp resulted in exactly what I saw on the dyno, spike with a couple of waves.

              Session two I used the forum recommended settings, boost Range to 150 and dynamic comp 10. MUCH BETTER, thanks. Target was 240 and system hit 250 but was far more stable. Still a slight spike

              Third session I adjusted offset only, boost range was still 150 with dynamic comp 10. Now target was 240 and the controller hit 240-243 so very smooth. However I still saw a slight spike.

              Session 4 I increased the boost range to 160 but thanks to a Miata dropping it's entire oil pan contents onto the track across 3 corners the session was red flagged. I only got into boost heavy once so not a big enough sample to tell how much of a difference this made. I did still see a spike.

              Question now is if I should raise boost range more? Say to 180?

              Comment


              • #8
                I would reduce the Dynamic Comp to 8 or maybe 7. You can send the log/s to customers@autronic.com.au if you want me to have a look at them.

                Comment

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