1998 Camaro speedometer reads way high with correct speedo section

[slarsen47]

It has been an interesting task going from a 98 Camaro roller to a running driving car.

Only issue before the turbo install is the 98 speedo reading way high with correct speedo section.

GPS reads 80 kph, HP Scanner reads 80 kph and speedo reads 100 kph (50, 50 and 62.5 in mph).

Car is 1998 Camaro, stock dash/engine harness, repinned 411 pcm with RTT, 2 bar and 4L80e segment swap.

Using 3219 for trans revs per mile which is correct for 25.7 stock tire.

And 128,766 for VSS pulses per mile. 4.1 gears Moser diff (to be changed to 3.25/3.50 with turbo).

I was originally stumped with the large ID1000 injectors and the VE table not responding low down, but a 0.028 transient was the key.

So now driving around and getting a decent SD open loop tune...........cars starts/runs/shifts great...........only issue is the 98 dash cluster speedo.

I am aware 98 cluster is different than 99-02 cluster and wiring.

Is this a known issue with 98 or am I missing something?

[2xLS1]

All P01 F-body calibrations use 24.91 for the stock tire height so if you are using 25.7 it is going to be off. This is what I get when just changing the gear to 4.10 on a stock 02 F-body A4 calibration using both older and newer software.

[slarsen47]

Thanks for that info.

Will try it tomorrow, storm clouds rolling in....lol

Edit: Just realized my HP Scanner speed matched the GPS, so the data end of things is correct.

Not sure how the dash reading can be so different then, but will try those numbers.

[slarsen47]

Below is my speedo setup for my original post where the scanner speed matches GPS but the speedo is 25 percent high.

Screenshot 2025-06-03 223102.png


Below is my speedo setup for 60 kph GPS perfectly matches the speedometer BUT the scanner shows 50 kph.

Screenshot 2025-06-03 222900.png


So increasing the VSS pulses by 25 percent fixed the speedometer error.

But also caused the scanner speed to NOT match the GPS.


I suppose the next step is to edit the trans revs per mile and leave the VSS pulses per mile alone.