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

[EYY]

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.

 

[Immortality]

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

 

[Stock AFM SS Wagon]

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.

 

[Immortality]

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%

 

[EYY]

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.

 

[Immortality]

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

 

[EYY]

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

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

 

[Immortality]

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.

 

[Stock AFM SS Wagon]

VT V6 onward you can just change the dash and the speedo is correct.

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

 

[Immortality]

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