Speedometer calibration for 3.90 gears 2008 Corvette

[realspeeddan]

I've got a 2008 Corvette in the shop that I want to calibrate for 3.90 gears.

The Final Drive in the tune is listed as 1.0

Should I adjust:
A) The VSS Pulse Per by the (new ratio/old ratio)

or

B) The VSS Tire Revs Per by (new ratio/old ratio)

or

C) Something else?

[Justinjor]

Interested to know the answer to this question myself. I'm doing 4.10s next month and will need to know what changes in the tune to reflect the different ratio.

[jim2092]

If it is a manual transmission no change is neccessary. Speedometer not based on gearing.

[2xLS1]

Vette VSS reads off the ring gear/axle revolutions. Those revolutions don't change with a gear ratio change for a given mph. Only with a tire size change. If it it an auto trans then you just scale the shift and TCC lock up tables by old ratio/new ratio.

[Justinjor]

So I just got my 3.90s installed and my speedo is now off 4mph. 80mph shows on the odometer but 76mph shows on the gps. I couldn't figure out why I kept getting passed on the highway but now it makes sense.

Nothing else changed except the 3.42 => 3.90 but now the speedo is off.
What can be done to get the calibration correct again? I could lie to the computer and say it has taller tires but I'm not sure that is the correct fix.

[Justinjor]

After thinking about it, the new diff came with an existing VSS and I did not swap them out when I changed diffs.

Is it possible that the new VSS is different even though the cores were both the 2006+ variety? I noticed the part number on the cases were slightly different and didn't think to swap out my VSS at the time.

[Justinjor]

So my rear end core came from a 2007 and according to all the 2006-2010 tunes in the repository, 2007 is the only year with different settings for the VSS. I'll use those and see if it takes care of the issue.

[Justinjor]

Just an update to this thread. Try as I might, I could not figure out what settings the tune needed to see to have the speedometer reflect the correct reading.

I tried the settings from a 2007 stock tune but it made things worse. I ended up multiplying my tire size by .95 and that took care of everything. I tested the speed at 80, 70, 60, 50mph with GPS and it was exactly correct.

[vette_c6]

this should help

http://www.hptuners.com/forum/showthread.php?t=36459

[carlrx7]

dont forget about this!

http://www.hptuners.com/forum/showth...highlight=gear

[realspeeddan]

I've got a 2008 Corvette in the shop that I want to calibrate for 3.90 gears.

The Final Drive in the tune is listed as 1.0

Should I adjust:
A) The VSS Pulse Per by the (new ratio/old ratio)

or

B) The VSS Tire Revs Per by (new ratio/old ratio)

or

C) Something else?

OK, similar question, but this time for a 2010 Camaro with an automatic. The car has 3.55 gears now. When the speedometer says 100mph (on the dyno, not the street) the actual wheel speed is 87 mph. I changes the final drive ratio in the tune from 3.27 to 3.55 it did not change the speedometer, What should I change to fix the speedometer and what should I do with the shift speed tables?