pcmhacking.net

i have just converted my VU SS from auto to manual, and kept the auto 3.07 diff and my speedo now won't read over 30kph after hours of scouring the net looking anything to help with working out the correct PPK i found this so i thought it would be a good idea to put it up here incase anyone else needs it, its meant for changing diff ratios but i figured i could work it for changing the box because the PPK is the same between them but they have different diff ratios

LS1 Auto 3.07 : 1
LS1 T56 3.46 : 1

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CurrentPPK / OldDiffRatio = Lambda

Lambda * New DiffRatio = NewPPK
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What i worked out for my car

6301 / 3.46 = 1821.0982685

1821.0982685 * 3.07 = 5590.77167

Thanks for posting

I just go though what ever tune has the same diff ratio and copy the changes over.

Or you can if the same VSS and drive/drive gears are used as would if the box is the same but only the diff is changed.

For example.

Old diff = 3.08
New = 3.23

Old PPK for 3.08 = 1250

New/old

3.23/3.08 = 1.0487012987012987012987012987013

multiply result by old PPK

1.0487012987012987012987012987013 * 1250

New PPK = 1310.8766233..

Round off decimal 1310.9


For a laugh, what's sad is new cars in accordance to ADR can be almost 3 times this difference in the example and be in spec lol

speedo output pulse comes from ecu, going from auto to manual your pulses frrom ecu will be a lot lower because the manual pulses 17ppk vs 40ppk from the auto.

you need to modify the ecu tune.