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Thread: boost bypass control??

  1. #1
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    boost bypass control??

    so i have been tuning my 2012 audi a7 since around november. car runs consistently 7.4s in 1/8 and 11.4-11.5s in 1/4. but i can not for the life of me figure out which table or tables control the boost bypass exactly. most times the bypass only closes (o%) when it shifts into 5th gear at top of pull. most of the pass it is around 5-15% open. commanded tq is around 750nm. if i change the airflow table to lets say 850. car just goes into limp mode and basically shuts down. any insight into this would be greatly appreciated. i just changed a bunch of stuff on the car and will need to redo the entire tune, so having a solid knowledge of this is a must at this point. i have added the tune and a 1/8 mile and 1/4 mile pull. as you can see, on this 1/4 mile pull the bypass opened alot causing boost to drop and my meth to turn off completely. thats why the lean issue and knock came in. thank you for your help
    Last edited by Hemithis01; 1 Week Ago at 10:11 AM.

  2. #2
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    So 22 people have looked at this and not one contribution? Has no one figured out full control of this system yet?

  3. #3
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    Cant tell you which table to adjust but if it is the same as the N75 on the Turbo cars 0% is wide open 100% is closed.

  4. #4
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    Ok so thanks to tyler coming to the rescue again!!! He has helped me a lot over the last few days. So there is not one single table that controls the boost bypass. It is controlled by the amount of torque requested vs actual torque. The ecu regulates the bypass to hit requested torque. So if your actual tq is higher than your requested tq. The ecu opens the bypass to try and lower actual tq output. If your not hitting the requested tq limit, then the ecu closes bypass in attempt to hit requested tq. If your actual tq is much higher than requested, the car will go into limp mode.

  5. #5
    Quote Originally Posted by Hemithis01 View Post
    Ok so thanks to tyler coming to the rescue again!!! He has helped me a lot over the last few days. So there is not one single table that controls the boost bypass. It is controlled by the amount of torque requested vs actual torque. The ecu regulates the bypass to hit requested torque. So if your actual tq is higher than your requested tq. The ecu opens the bypass to try and lower actual tq output. If your not hitting the requested tq limit, then the ecu closes bypass in attempt to hit requested tq. If your actual tq is much higher than requested, the car will go into limp mode.
    Technically the effective area and predicted angle have direct control, but you shouldnt modify those unless you change the bypass out.
    Air control ultimately comes from torque control, and thats the best way to tune it.

    What the ECU is doing is controlling the bypass as a second throttle, designed to control the manifold pressure directly by venting excess out.
    So the best way to control it, is to control what it desires as manifold pressure, which is all via torque control
    If its not broke, just give it time.

  6. #6
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    Quote Originally Posted by Steven@HPTuners View Post
    Technically the effective area and predicted angle have direct control, but you shouldnt modify those unless you change the bypass out.
    Air control ultimately comes from torque control, and thats the best way to tune it.

    What the ECU is doing is controlling the bypass as a second throttle, designed to control the manifold pressure directly by venting excess out.
    So the best way to control it, is to control what it desires as manifold pressure, which is all via torque control
    so am i right in thinking the torque model maps are actual and requested tq? aircharge to tq table would be actual tq and tq to aircharge table would be requested tq? if i look at that way, the number seems to make more sense.

  7. #7
    Quote Originally Posted by Hemithis01 View Post
    so am i right in thinking the torque model maps are actual and requested tq? aircharge to tq table would be actual tq and tq to aircharge table would be requested tq? if i look at that way, the number seems to make more sense.
    Yessir.
    Almost all modern torque based ECUs function similarly! You get a torque request, its converted to an aircharge request, which is converted to a MAP request, which becomes the driving force behind throttle/bypass/wastegate controls. Of course thats grossly simplified because they all do it slightly differently, but in this case, you're dead on.

    The Actual Torque is estimated based on what it believes the aircharge to be using that table. This aircharge can be from a MAP sensor (via speed density), MAF sensor, or some combination. The Requested Torque is what is fed into the Tq to Aircharge table to get a desired aircharge. This then goes through an "inverse" speed density equation to get a desired MAP used to control the the necessary actuators.
    If its not broke, just give it time.

  8. #8
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    Quote Originally Posted by Steven@HPTuners View Post
    Yessir.
    Almost all modern torque based ECUs function similarly! You get a torque request, its converted to an aircharge request, which is converted to a MAP request, which becomes the driving force behind throttle/bypass/wastegate controls. Of course thats grossly simplified because they all do it slightly differently, but in this case, you're dead on.

    The Actual Torque is estimated based on what it believes the aircharge to be using that table. This aircharge can be from a MAP sensor (via speed density), MAF sensor, or some combination. The Requested Torque is what is fed into the Tq to Aircharge table to get a desired aircharge. This then goes through an "inverse" speed density equation to get a desired MAP used to control the the necessary actuators.
    Thank you for the simplifying that for me. Lol do you know exactly what the supercharger airflow table co trol and how to dial it in? What pids would you datalog for that table? I have tried adjusting it up and down but i can not figure out exactly what it controls. Thanks

  9. #9
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    Hemithis your tune is labeled new throttle body . Did you put a 80mm body on your car? I?m currently running an S5 with 3.33 ratio pullies. At 4500 feet elevation I can?t get more than about 195kpa absolute manifold pressure with 0 opening on the bypass valve. I?m also struggling to get the tune to give the car any ignition timing. How did you get so much advance on your tune