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Thread: Intake Manifold Absolute Pressure (SAE) reading is way way off

  1. #1
    Tuner Turbo6TA's Avatar
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    Intake Manifold Absolute Pressure (SAE) reading is way way off

    2011 Corvette LS3 (Gen 4) with Magnuson 'Heartbeat' supercharger

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    I just started using the HP Tuners and did a log file with the VMC Scanner today.

    I know that my max boost from this supercharger is about 7 PSI, but today, when logging "Intake Manifold Absolute Pressure (SAE)" it showed 22 PSI of manifold pressure when at WOT @ 6,200 RPM.

    Now, I know for a fact that this supercharger don't make anywhere near 22 PSI of boost.

    Any idea as to what is going on here ?

    Thanks,
    Ron

  2. #2
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    I would look at your MAP scaling.

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    Tuner Turbo6TA's Avatar
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    Unfortunately, I don't have a clue as how to re-scale the MAP. The car was professionally dyno tuned after the supercharger was installed.

    The MAP sensor is the standard LS9 sensor that is supplied with the Magnuson supercharger kit.

    The car runs great, but why it don't show the correct boost pressure using HP Tuners had me confused.

    Looking at the file, I see that the Intake Manifold Absolute Pressure (SAE) shows 8.3 PSI during idle ... just ain't right !

  4. #4
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    Absolute pressure means in a perfect vacuum it'll read 0psi. At atmospheric pressure it'll read around 14.7psi +/- a bit depending on weather and altitude.

    You need to create a custom math parameter.
    MAP abs - Baro = Boost

  5. #5
    Tuner Turbo6TA's Avatar
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    I guess I need to figure out how to create a custom math parameter.

    Here is a photo of the log file showing the 22 PSI boost at the top of a WOT acceleration in 3rd gear (A6 trans):
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  6. #6
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    Take the Part number off your map sensor. Search for the data and offset. On your engine> Airflow tab you will have the spots to put that info.

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    Well, I found it for the LS9 . 3-BAR sensor . . P/N: 12592525

    Linear (312.50 kPa)

    Offset (-11.25 kPa)
    ___________________________________

    I am thinking that the "Linear" would go where it says "Slope" in the photo above, and "Offset" would obviously go in the "Offset" photo above ? ?





    Oh Wait ... I see those 312.50 and -11.25 numbers are already included in the "Characteristics MAP Sensor Linear and Offset" sections of the photo I posted above.
    Last edited by Turbo6TA; 12-10-2021 at 04:53 PM.

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    yes if thats the sensor you have

  9. #9
    Tuning Addict 5FDP's Avatar
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    No, the linear and offset setting are already in there for the MAP sensor. You don't touch the BARO settings.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  10. #10
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    So, how would I get the it to read my correct 7 PSI (give or take) boost at WOT ?

  11. #11
    Tuning Addict 5FDP's Avatar
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    Post #4 told you what you gotta do. Make a custom math channel for boost and then that channel will read what you want.

    Or just learn to read MAP kpa in the logs to determine boost. That's what I do anyway for most things.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  12. #12
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    Quote Originally Posted by 5FDP View Post
    Post #4 told you what you gotta do. Make a custom math channel for boost and then that channel will read what you want.

    Or just learn to read MAP kpa in the logs to determine boost. That's what I do anyway for most things.
    Well, that's what I need to do ... Unfortunately I don't have a clue how to even start making a 'custom math channel' (sounds like Rocket Science to me)

    Please excuse my ignorance

  13. #13
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    I tried to post a copy of my tune here ... I right clicked the tune and then copied it ... then tried posting it here, but it never showed up in my post to you.

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    Thanks hjtrbo ...

    It now shows up in the Math Parameters Manager .. under 'Maths-User' .. with the name 'Boost'

    So, the next time I log a run, I will get the correct boost pressure value next to Intake Manifold Absolute Pressure (SAE) ???

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    just add it to your chart v time with min/max values and it should work fine, just make sure in the maths when selected that the pids are not red where hjturbo showed ID box

  17. #17
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    In my Math Parameters Manager . . ID 6100 . . Name: Boost



    The ID 50030 > Manifold Absolute Pressure [Sensor] is not red

    The ID 50032 > Barometric Pressure [Sensor] is red


    Last edited by Turbo6TA; 12-10-2021 at 07:48 PM.

  18. #18
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    u need to add that baro to the channels list, press the gear with the green + on it and u get the list of pids then u can type in the 50032 to find the baro then add it in the list and it should remove the red next time u connect the vehicle and log, then that boost pid will work

  19. #19
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    You guys 'down under' have been a great help !

    Ok, the red color disappeared ... It's nighttime here right now. I will do a log in the morning and see if this works.

    Thanks a bunch for you and everyone else that has helped me through all this.

    I just got this HP Tuners about a week ago, and I feel like a real idiot trying to explain all this to you folks that obviously know a hell of a lot more about HP Tuners than I will probably ever know.

    Again, thanks ...

    This will more than likely not be the last time you hear from me and my silly questions.

    Ron,

  20. #20
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    BTW ... Here is the Corvette ...





    Last edited by Turbo6TA; 12-11-2021 at 07:52 AM.