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

[EYY]

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.

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:

if you want an easy painless method of having everything work correctly, then leave the pcm alone, you dont really need to touch the ppk or shift points in the pcm. just install jaycar corrector between the pcm and speedo in your dash and adjust it up. all shifts will be perfect and dash will read correctly

Yoda69:

Speedo into PCM is back of gearbox, what happens after this the ECU doesn'r care about, ie. the diff ratio and tyre size.
If the PCM was using the ABS wheels speed sensors for vehicle speed, then would need to redo all thye gear change setting as this is taken post diff.

Both in same thread: https://pcmhacking.net/forums/viewtopic.php?f=7&t=1607

I think speed sensors are very misunderstood.

 

[Immortality]

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.

If you change the diff ratio from a 3.08 to a 3.45 this is a 12% reduction so speedo will read 12% higher than true speed. ie. 100km/h vehicle speed wil show 112km/h on the speedo.
From an ECU point of view, the engine speed into the transmission to the output speed of the transmission stays the same, although the data in the ALDL will read 12% out. This data is then outputted to the speedo and the error remains which is why the speedo is wrong.
If you fix it on the ECU by correcting PPK from speedo input, you will then need to update every table/scalar that references vehicle speed, 1-2, 2-3, 3-4 up/down shifts, power/normal/cruise, TCC lock/unlock max speed in gears, etc to correct them, easiest way would be to multiply the whole table by 0.88 to lower all the speeds by 12%, but typically not all tables/scalars are in the xdf, so you may have now created a new problem. Looking at the $11 XDF which is well defined for the trans, with a quick look there nearly 50 Tables that would need to be adjusted.

yoda69

Taken from the same thread you linked above (the $11 tune is for the VR V8 with 4l60e)

 

[Stock AFM SS Wagon]

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

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

 

[EYY]

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)

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.

 

[Immortality]

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.

 

[EYY]

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.
View attachment 205098

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

 

[Immortality]

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

It does, until you change the ppk number.

 

[EYY]

It does, until you change the ppk number.

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

 

[Cuzzy69]

fixed!!!!! 60 is close, 80 is 80 and 100 is 100. under 60 its under reading but who cares lol. take off the needle and move it downward about 10mm. i put a new srcew to hold the needle at 0. i changed from a 3.08 to 3.89 diff. you may need to play abit with the needle location using gps to chk it out.. marks 4wd adaptors sell a correction kit for about $250 that is gardened to work.

 

[losh1971]

fixed!!!!! 60 is close, 80 is 80 and 100 is 100. under 60 its under reading but who cares lol. take off the needle and move it downward about 10mm. i put a new srcew to hold the needle at 0. i changed from a 3.08 to 3.89 diff. you may need to play abit with the needle location using gps to chk it out.. marks 4wd adaptors sell a correction kit for about $250 that is gardened to work.

Interesting, I can't in my head see how moving the needing can make it accurate? I have 3.45s and mine reads out by 10%. If I was to move the needle 10% it might be accurate at one speed but it's still going to be out at another speed. See mine is out by 10kph at 100kph, however if I was to drive at 70kph on the speedo I am still speeding in a 60kph zone by 4kph. Therefore I am surprised that altering a needle position can make it accurate at anymore than one speed.