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  1. #1

    RXPX motors and the sweet spot RPM

    Since the release of the latest release of MegaLogViewer HD and the Table Generator, I have moved over to autotuning these motors. In simple terms, I use the imbedded capability of the software to use statistics to calculate the next VE (or Engine Efficiency in the Motec world) The good news is that you do not need to understand statistics to see the tuning results.

    The first bit of EFI tuning that helps to get your head around is horsepower and airflow is driven by MAPxRPM. Increase either one and HP gennerally goes up. The thing that gets involved in this is Volumetric Efficiency and the HP formula is really MAP x RPM x VE.

    So as long as your VE stays up, all you need to do is increase RPM or MAP.

    Now that I am using the Autotune in MLV HD an interesting thing popped to light. These motors (at least the one I am tuning has a huge dip in VE right at 8300 RPM. No wonder people all say that these motors feel best at 8900-9000 RPM. These motors peak VE at 7500 RPM, plunge to a hole in efficiency at 8200 –8300 and then come ripping back at about 8900 RPM

    See the plot below.

    http://www.nbs-stl.com/RxpxTuning/En...gine%20Eff.png

    Way cool stuff. All we need to do is have data and be willing to look at it.

    The same autotune works fine on VTech and CMD. The math changes a bit but I can help anyone thru that part.

    I did a little video of MegaLogViewer HD, the tuning/log viewing software that I am using.



    Have fun tuning whatever you ride.

    Andy
    Last edited by whittlebeast; 02-06-2015 at 10:42 AM.


  2. #2
    Here is the AFR plot for the same data log.

    http://www.nbs-stl.com/RxpxTuning/Race%20AFR%20Plot.png

    And the average AFR grouped for the Motec Tuning SW

    http://www.nbs-stl.com/RxpxTuning/ML...gram%20AFR.PNG

    Andy

  3. #3
    800AMSOIL4U's Avatar
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    Thanks for the great information.

  4. #4
    Branden's Avatar
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    im curious as to why there is a dip in efficiency around 8300, i wonder if it could be contributed to the cam profile? These motors seem to really wake up when a bigger cam is put in place of the stocker. Maybe chamber design? Either way, that is cool info.

  5. #5

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    thank you for sharing

  6. #6
    I would need more Motec data to see if the pattern repeats or is unique to this ski.

  7. #7
    Branden's Avatar
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    Quote Originally Posted by whittlebeast View Post
    I would need more Motec data to see if the pattern repeats or is unique to this ski.
    that just seems like an odd place to have a dip. has anyone seen a dyno graph of one of these motors? I would be curious to see if that graph shows something similar around the 8300 area.

  8. #8
    800AMSOIL4U's Avatar
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    What mods are done to this motor? Aftermarket Cam, springs, intake manifold etc?
    Last edited by 800AMSOIL4U; 02-06-2015 at 01:30 PM.

  9. #9
    Moderator beerdart's Avatar
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    Interesting its right at/around the factory rev limit.

  10. #10
    Martin RXT-X's Avatar
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    Andy,
    Where did you find the MAP X RPM channel

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