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Thread: Dyno sais 12.85 AFR. Is it really that?

  1. #1
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    Dyno sais 12.85 AFR. Is it really that?

    If the dyno has a stoich of 14.67 and I have a stoich of 14.19 for E10 is the 12.85 AFR really about a 12.4 AFR?

    14.19/14.67 x 12.85 is around 12.4

    Or is afr just that?
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  2. #2
    Tuning Addict 5FDP's Avatar
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    Hopefully I don't confuse myself here but stoich is stoich and for your case it's E10/14.13ish or so. So then you'd just still commanded whatever AFR you want to run based off the stoich/fuel you are using.

    Are you saying the dyno place runs E0 fuel??
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  3. #3
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    Quote Originally Posted by 5FDP View Post
    Hopefully I don't confuse myself here but stoich is stoich and for your case it's E10/14.13ish or so. So then you'd just still commanded whatever AFR you want to run based off the stoich/fuel you are using.

    Are you saying the dyno place runs E0 fuel??


    I thought as part of the dyno they enter in their own stoich value. I was told they have theirs dialed in as 14.67. I have mine at 14.13. You are correct. Not 14.19.

    Knowing nothing about dynos is it then true they have to plug in a stoich or is there no such item?
    2016 Hellcat Challenger, automatic, black on black with brass monkey wheels

    10.13@ 140 DA 5000 feet
    2.75 pulley, tune, drag radials. 10 percent lower od crank pulley, 1050 ix. off road mid pipe. tune

  4. #4
    Senior Tuner Higgs Boson's Avatar
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    have to think in terms of lambda. AFR is a conversion.

    if stoich in the tank is 14.2 and stoich on the dyno is 14.7 then both = lambda 1.0

    target the lambda for whats in the tank and multiply it by the dyno stoich afr and you will have your dyno afr target.

    or just set everything up for lambda and stop converting.

  5. #5
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    Quote Originally Posted by Higgs Boson View Post
    have to think in terms of lambda. AFR is a conversion.

    if stoich in the tank is 14.2 and stoich on the dyno is 14.7 then both = lambda 1.0

    target the lambda for whats in the tank and multiply it by the dyno stoich afr and you will have your dyno afr target.

    or just set everything up for lambda and stop converting.

    So this has already happened where the stoich on the dyno was 14.67 and my stoich was 14.13.

    The p.e. was set to 1.17. That gives a lambda of a little over .85

    14.67/1.17 is 12.53

    The dyno read 12.85.

    12.53/12.85 is around .975

    It seems to me that I should enrichen the maf calibration by 2.5% upwards to attain the 12.53 on the dyno. (theoretically)

    And then we would get 14.13/1.17 = 12.07 on E10. (what I have in my tank and it has been tested)

    Is that correct or did I make it too complicated. I cannot get back on the dyno for a while.
    2016 Hellcat Challenger, automatic, black on black with brass monkey wheels

    10.13@ 140 DA 5000 feet
    2.75 pulley, tune, drag radials. 10 percent lower od crank pulley, 1050 ix. off road mid pipe. tune

  6. #6
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    If the dyno thinks stoich is 14.67, and it's reading 12.85, then it's reading Lambda 0.876.

    If you're commanding PE to 1.17, then that's Lambda 0.855.

    100*(actual - commanded)/commanded = % error.

    100*(0.876-0.855)/0.855=2.46% error.

    This means you're 2.46% lean.
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  7. #7
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    Quote Originally Posted by MikeOD View Post
    If the dyno thinks stoich is 14.67, and it's reading 12.85, then it's reading Lambda 0.876.

    If you're commanding PE to 1.17, then that's Lambda 0.855.

    100*(actual - commanded)/commanded = % error.

    100*(0.876-0.855)/0.855=2.46% error.

    This means you're 2.46% lean.


    I appreciate the help Mike. That is what I thought.
    2016 Hellcat Challenger, automatic, black on black with brass monkey wheels

    10.13@ 140 DA 5000 feet
    2.75 pulley, tune, drag radials. 10 percent lower od crank pulley, 1050 ix. off road mid pipe. tune