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Thread: Ford Trans Tuning Tip - N/V Base

  1. #1
    HPT Employee Eric@HPTuners's Avatar
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    Ford Trans Tuning Tip - N/V Base

    I've been getting quite a few questions from people that are having issues with getting the transmission to shift at the correct time.

    Ford PCMs calculate a value called N/V (N over V).

    N = Engine Speed
    V = Vehicle Speed



    In the screenshot above is the starting value for N/V. This is the N/V the stock shift schedule was calibrated for. If there were axle ratio changes, or tire size changes, this value is wrong.

    The PCM can learn the N/V somewhat, but there are clips for how far it can go. If the PCM ends up clipping the N/V value, you will run into issues getting the transmission to shift on time.

    The Base N/V value is divided by the N/V it comes up with (clipped or not) and the resulting value is a correction factor. This correction factor is used to adjust the vehicle speed coming from the VSS.

    Bottom line is the Base N/V needs to be pretty close to accurate.

    I've found the easiest way to determine what value to use is to run the car on a dyno, in the 1:1 gear ratio with the converter locked, and look at the calculated gear ratio. (See Below).

    Eric Brooks
    HP Tuners, LLC

  2. #2
    It looks to be the same for every auto vehicle i have the stock file for no matter what gears or tire size. Wouldn't it be different for a mustang vs a f150?

  3. #3
    Advanced Tuner Witt's Avatar
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    A formula you can use if you don't have a dyno handy after a gear or tire change is:

    (rear gear ratio*tire rev per mile)/60

  4. #4
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    I'm having this issue now with my 2013 GT. It should be shifting at 6800 but hitting a limiter at 7200 then shifts. So in my case I would use 3.15*707/60 = 37 for the N/V Base?
    Should I keep "Use VID" enabled or disabled?
    2013 Mustang 5.0 A6
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    HPT Employee Eric@HPTuners's Avatar
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    Quote Originally Posted by imsuperman View Post
    I'm having this issue now with my 2013 GT. It should be shifting at 6800 but hitting a limiter at 7200 then shifts. So in my case I would use 3.15*707/60 = 37 for the N/V Base?
    Should I keep "Use VID" enabled or disabled?
    Use VID = Disabled, else the changes you make will not take effect.
    Eric Brooks
    HP Tuners, LLC

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    Quote Originally Posted by Eric@HPTuners View Post
    Use VID = Disabled, else the changes you make will not take effect.
    What about the "VSS P/REV - Trans" and "N/V Min Learned", leave those at default?
    2013 Mustang 5.0 A6
    Procharger P1SC1 STGII w/4" pulley = 10lbs
    DW 95lb Injectors
    Lethal Performance O/R X-PIPE
    Borla S-Type
    -----------------------------------------------------
    2016 Ford F250 6.7L
    Stock

  7. #7
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    I following this post: And almost correct all my shift commanded issues. The car is a 2013 Mustang GT with A6. Is shifting as comanded (7000 rpms) in 2,3,4 gears. But in the 1st gears and the car is accelerated from a full stop is commanded to 7000K but shifts 6200K rpm. But is the car is rolling at 5 mph the car shifts as commanded.

    The car has hoosier drag radials and i not see any spin issues.

    What can be?

  8. #8
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    Use VID = Disabled...????.. sorry if this is a dumb question but what is VID and where is it located. I just swapped from stock 3.15 to 3.73 and was looking on the forum for all the changes that I need to make and that kinda stumped me. I looked everywhere and have not seen "Use VID" I have a 2012 Mustang GT.

  9. #9
    Advanced Tuner 96gt4.6's Avatar
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    I'm needing some expert help on this as well....

    I corrected my N/V values as per the recommendation, which changed it from 40 to 43.

    I have the trans shift values set to 6800 RPM, with all the limiters at 7200 RPM. I'm getting some shift inconsistencies, primarily on the 1-2 shift. It always wants to shift early, usually around 6500 give/take. I've logged the event, and i'm not hitting the 1-2 MPH shift table which is set at 40 mph (shift is happening around 38 mph). I've also moved the vehicle max accel to double the factory value for the RPM anticipated shift.

    This is in a 2003 Marauder swap.

    Can I get someone to double check my values? I have attached a tune and log. In this tune, the N/V is set to 45 (I had calculated 43) as I was just guessing to see if that changed it. The 1-2 is still early, but the 2-3 seems right.

    1-2 Shift Point:



    Tune Values:



    My current gear ratio is 3.55, running 245/55/18's for rear tires.


    Any help appreciated guys, thank you in advance!

    Here's the Tune and Log:



    6800 Shifts, Final Tune (CURRENT TUNE).hptLow Shift Log 1.hpl
    Last edited by 96gt4.6; 09-16-2015 at 03:02 PM.
    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

  10. #10
    Advanced Tuner 96gt4.6's Avatar
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    Quote Originally Posted by just2012gt View Post
    Use VID = Disabled...????.. sorry if this is a dumb question but what is VID and where is it located. I just swapped from stock 3.15 to 3.73 and was looking on the forum for all the changes that I need to make and that kinda stumped me. I looked everywhere and have not seen "Use VID" I have a 2012 Mustang GT.
    VID is your Vehicle Identification Data block. There should be a drop down box that will allow you to Enable or Disable it. Drop that down to Disabled, then populate your values for your tire rev/mile and gear ratio, that will let the PCM use your values, and not the ones stored in the VID block. Otherwise, as Eric stated, whatever is put in those tables the ECU will not use.
    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

  11. #11
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    96gt4.6, could you try trans/general/normal RPM limit all cells down to 5000 RPM please?
    Last edited by kdanner; 09-18-2015 at 08:00 AM.

  12. #12
    Advanced Tuner 96gt4.6's Avatar
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    Quote Originally Posted by kdanner View Post
    96gt4.6, could you try trans/general/normal RPM limit all cells down to 5000 RPM please?
    I just realized that I had missed this reply, sorry about that! I will try and pay closer attention to my InBox.

    What is your question/request pertaining to? If i'm reading correctly, moving those tables down to 5,000 rpm will result in hitting the RPM limiter set by the trans. This had to actually be raised to shift above 6k, for me, originally, as i'm using a truck PCM/base tune.
    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

  13. #13
    Advanced Tuner 96gt4.6's Avatar
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    There is also an easier way to calculate the N/V, at least for me. All you need is driveshaft speed in RPM, which can be obtained with the following information.

    Values needed:

    Tire Diameter (Pi x measured diameter)
    Tire Rev/Mile (63360 - inches in a mile / Tire Diameter from step above)
    Gear Ratio
    Calculated Driveshaft Speed (Tire rev per mile x gear ratio)

    Take your calculated driveshaft RPM from the formula above. Once you have the driveshaft RPM calculated, you now know engine RPM, as in your 1:1 gear, driveshaft RPM equals engine RPM. Us 6R80 guys have no 1:1 gear, so this method is how I had to obtain this. Being as we've converted to Rounds Per Minute, you can now use 60 MPH as your speed which makes the math easy. Take your calculated driveshaft (engine) speed and divide it by 60. This is your N/V value, and will be percise as long as your tire diameter and gear ratio are accurate. No dyno or actual measurements of vehicle speed or RPM needed.
    Last edited by 96gt4.6; 11-19-2015 at 08:11 AM.
    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

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    Quote Originally Posted by 96gt4.6 View Post
    I just realized that I had missed this reply, sorry about that! I will try and pay closer attention to my InBox.

    What is your question/request pertaining to? If i'm reading correctly, moving those tables down to 5,000 rpm will result in hitting the RPM limiter set by the trans. This had to actually be raised to shift above 6k, for me, originally, as i'm using a truck PCM/base tune.
    I experienced some early shifts as you have, lowering this corrected them.

  15. #15
    Advanced Tuner 96gt4.6's Avatar
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    Quote Originally Posted by kdanner View Post
    I experienced some early shifts as you have, lowering this corrected them.

    Interesting!

    I had to raise this table to get the shift RPM where I had it set in the shift RPM tables. Setting it lower, or close, to my shift rpm results in the logged TQ source changing to 'RPM Limiter' and a delayed shift.

    Are you using a Mustang computer/OS, or F150? Here's my current settings:

    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

  16. #16
    Quote Originally Posted by 96gt4.6 View Post
    There is also an easier way to calculate the N/V, at least for me. All you need is driveshaft speed in RPM, which can be obtained with the following information.

    Values needed:

    Tire Diameter (Pi x measured diameter)
    Tire Rev/Mile (63360 - inches in a mile / Tire Diameter from step above)
    Gear Ratio
    Calculated Driveshaft Speed (Tire rev per mile x gear ratio)

    Take your calculated driveshaft RPM from the formula above. Once you have the driveshaft RPM calculated, you now know engine RPM, as in your 1:1 gear, driveshaft RPM equals engine RPM. Us 6R80 guys have no 1:1 gear, so this method is how I had to obtain this. Being as we've converted to Rounds Per Minute, you can now use 60 MPH as your speed which makes the math easy. Take your calculated driveshaft (engine) speed and divide it by 60. This is your N/V value, and will be percise as long as your tire diameter and gear ratio are accurate. No dyno or actual measurements of vehicle speed or RPM needed.
    Just to confirm, for gear ratio you are referring to axle gear ratio right?

    So if I have a 4.10 rear axle gear, then it becomes (tire rev per mile X 4.10) right?

  17. #17
    Advanced Tuner 96gt4.6's Avatar
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    Quote Originally Posted by dbb2797 View Post
    Just to confirm, for gear ratio you are referring to axle gear ratio right?

    So if I have a 4.10 rear axle gear, then it becomes (tire rev per mile X 4.10) right?
    Correct. (tire rev/mile x 4.10) = Driveshaft speed. Driveshaft speed/60=N/V Value.
    '17 Whipple'd S550
    Too many other projects to list.....see my YouTube channel for more: https://www.youtube.com/channel/UCr7...-XfDG53sCh6tcw

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    Quote Originally Posted by 96gt4.6 View Post
    Are you using a Mustang computer/OS, or F150?
    Mustang. When I had it raised it would shift at only around 6800 no matter how high I had the WOT shift by RPM scalars and/or upshift by MPH functions.

  19. #19
    Sorry to bump an old thread. For whatever reason my car refuses to accept any changes. i only have the 3 tables, final drive, VSS tire speed, and N/V base. i had set revs to 724 as per the tire manf. No change. Speedo reads 5mph slow. then found this thread and did the N/V ratio. 40.3, no change. Went out and changed revs to 633 as per the difference, no change. Am i missing somehting? This is on 3.0.40 for a 14 mustang btw
    Last edited by thegraystang; 03-03-2016 at 09:24 PM.

  20. #20
    Advanced Tuner Witt's Avatar
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    Quote Originally Posted by thegraystang View Post
    Sorry to bump an old thread. For whatever reason my car refuses to accept any changes. i only have the 3 tables, final drive, VSS tire speed, and N/V base. i had set revs to 724 as per the tire manf. No change. Speedo reads 5mph slow. then found this thread and did the N/V ratio. 40.3, no change. Went out and changed revs to 633 as per the difference, no change. Am i missing somehting? This is on 3.0.40 for a 14 mustang btw
    Make sure "Use VID" is disabled.

    Also make sure the "Use Tire Circ. and "Use Final Ratio" are enabled if available, I think only the trucks use this parameter though.
    Last edited by Witt; 03-03-2016 at 10:01 PM.