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diff ratio change. speedo correct! yer i know pls read

Discussion in 'Mace Engineering' started by Cuzzy69, Nov 1, 2018.

  1. EYY

    EYY Well-Known Member

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    Only real issue with doing it that way is the torque converter lockup speeds are all messed up. Trans shifts themselves aren’t effected in my experience.
     
  2. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    And still does not fix the speedo issue as the PCM does not modify the signal to the dash for anything from VN - VS.
     
  3. Stock AFM SS Wagon

    Stock AFM SS Wagon New Member

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    Torque converter locks up will be messed up yes, I just lived with it, did it to a VS V6 auto and a VX V6 auto, 3.23 on the VS & 3.46 (V8 manual diff) on the VX, to be honest the box's took a few days to learn to change at red line but soon adapted, from memory the PPM change can be done on VS, definatley VX, to make speedo run true, BUT, I am getting older and memory a little fuzzy lol, pretty sure it worked but.
     
  4. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    VT V6 onward you can just change the dash and the speedo is correct. VS and earlier is a different kettle of fish. Torque converter lock up and shift points all work off TPS Vs road speed, if you alter the PPM in the tune all of these will be stuffed up unless all of these years I've been tuning these wrong?

    3.08 to 3.23 is **** all change, just 5% and would barely make a change to the shift points or the speedo which from the factory read fast about 4% (reading about 104km when doing 100), even 3.08 to 3.46 is only 11%
     
  5. EYY

    EYY Well-Known Member

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    I did my vx ss - 3.07 to 3.91. Still drove nicely without issue, but lockup was the only thing effected as it locks up earlier because the computer thinks that roadspeed is higher. This is no issue though due to the increased mechanical advantage of shorter gears, and rpm for lockup remains the same.

    Really, the pcm gets all info from the transmission extension housing forwards, so it doesn't know or care what the actual roadspeed is for most parameters. Some (if not all) pcm's have roadspeed as a trigger for converter lockup and lean cruise but that's it from memory - may be more parameters that i'm not aware of though. Changing just the cluster ppk isn't perfect, but it's good enough for most situations it seems.

    Shift points are mainly effected on models where the pcm takes readings of axle speed, not output shaft speed.
     
  6. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    The PCM calculates road speed based on the ppk value. LS is a bit different, different PCM.
     
  7. EYY

    EYY Well-Known Member

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    Yes different pcm, but i would expect it would use ppk data in the same way?
     
  8. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    Yes and no, totally different operating systems and different communications etc. LS type pcm's uses adaptive shift I believe where the earlier stuff didn't although it was in the software.
     
  9. Stock AFM SS Wagon

    Stock AFM SS Wagon New Member

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    Are you saying there is something behind the cluster that's can be adjusted?
     
  10. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    No, you have to reprogram the cluster. There is software available to do so.
     
  11. EYY

    EYY Well-Known Member

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    Adaptive shift shouldn't matter imo. I think the only reason they do the ratio corrector for these is that the cluster cannot be programmed for tech 2 to a high enough ppk... I have a feeling that Tazzl's software overcomes this limitation. I've been able to adjust a number of different clusters from vz-vz for different ratios without issue. @Sandman has found the limitations of the tech 2 in this regard.

    Just did a little more reading on pcmhacking.
    Jayme:
    Yoda69:
    Both in same thread: https://pcmhacking.net/forums/viewtopic.php?f=7&t=1607

    I think speed sensors are very misunderstood.
     
  12. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    There are conflicting answers, my original reply to the OP was to use a corrector box and this is the best answer for anything VN-VS. VT onward can be reprogrammed as you mentioned by Tazzi's software. I don't think the VSS is misunderstood, you just need to understand what it measures and what effect it has on the tune. Yes the VSS does not care about what happens after the gearbox (diff ratio and wheel size). All the shift speeds in the tune are set based on road speed and are worked out so the engine shifts at the correct rpm (calculated with the stock diff ratio/wheel size), change the ppk value and all these parameters get screwed up which is why it easier to just correct the speedo signal (to the dash) and leave everything else alone.

    There are a fair few parameters that are effected by road speed but most wouldn't care if it's a few km slower or faster as it effect things behind the scenes the driver is never aware off. In a manual car it's important as it controls when the PCM goes into idle mode. It also gets interesting when you start playing with cams because all the shift speeds are based off road speed so to make use of a cam all the shift points need to be moved up to get the engine to rev and make use of new power band.

    Taken from the same thread you linked above (the $11 tune is for the VR V8 with 4l60e)
     
    Last edited: May 13, 2019
  13. Stock AFM SS Wagon

    Stock AFM SS Wagon New Member

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    Ok cool, when I was doing all this it was 16 years ago and at the time this was the only way to do it or so i was told, so agreed easier/better to do what you have said :)
     
  14. EYY

    EYY Well-Known Member

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    Yes, tuning is definitely the best option for VN-VS and isn't difficult or expensive to do. Changing a cam you'd naturally alter 'roadspeed' anyway so that you're in the realm of the cam's operating rpm - it doesn't necessarily care what roadspeed is; just raise the number according to how hard you want it to rev. Either way, the pcm measures pulses, and no of pulses will be the same for upshift and downshift regardless of what the axles are doing.

    Eg. with 3.07 gears you'll upshift at a calculated roadspeed of 65kmph at 5500 rpm with a specified pulse count. With 3.91 gears, it may upshift at 55kmph because the pulse count is still the same at 5500rpm. Roadspeed is just a derived figure and doesn't effect trans shifts from everything I've read.

    Everybody that says it effects transmission shifts can't back it up at all with either first hand experience or documentation from what I've read - that's what I mean when I say the VSS is understood. I spent hours and hours reading about it all before I changed the diff in my ss but couldn't find any rock solid answers.

    Anyway all I'm trying to say is I can't understand why people say they need to be tuned to alter shift points, when the shift points effectively don't change from what I can gather for vr-vz for all engine variants. Of course if you're going to have the car tuned anyway, it's definitely worth setting the ppk correctly to begin with.
     
  15. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    I can. Tuned a mates VS L67 with diff change, I think it now has 3.89 when he had 3.45's before and to make it all the more fun he added an XP hot cam. We had lots of fun playing with shift points :) As you can imagine, I had to alter a LOT of tables to make it all happy. Didn't fix the speedo though, still needed a speedo corrector box for that.

    This is a screen shot from a VX L67, check out the 1-2-3-4 upshift table, it's all calculated on road speed. Check out all the other tables on the LH side for the auto, everything uses road speed.
    Shift tables.jpg
     
    EYY, 07GTS and Stock AFM SS Wagon like this.
  16. EYY

    EYY Well-Known Member

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    Roadspeed changes in proportion with your diff ratio change. So all stays in check. That’s my whole point.
     
  17. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    It does, until you change the ppk number.
     
  18. EYY

    EYY Well-Known Member

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    Yeah looks like we’ve been in agreement then lol, I just didn’t realise it :p
     

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