nj02vette

iTrader: (2)

Just spent last night helping a friend install 3.91's in his 06 GTO, replacing the 3.46's.

He took off and called me on the way home telling me his speedometer was off.

I thought manual cars didn't need any sort of programming plus I thought the VSS on GTO's were on the output shafts like the vettes, so no changes necessary.

Someone tell me why I'm wrong.

PS: I have HP Tuners so it's not a big deal to reprogram. Just curious as to why.

adam1803

iTrader: (65)

The ECM still needs to know the ratio so that it can convert the VSS signal to the correct speed. AFAIK you have to calibrate for gear swaps on every car either through speedo gears or the ECM.

nj02vette

iTrader: (2)

Thanks for the reply.
On Corvettes, you absolutely do not have to do this, since the pulse on the output shaft will only vary as the shaft is rotated (aka MPH), the only thing that affects speedometer would be tire diameter size (after the VSS). The ratio doesn't need to be updated since it never changes.

On F-bodies, the VSS is in the transmission, so everything after will affect it including gears and tire sizes.

On the GTO, which I'm not to familiar with, I thought the VSS were on the output shafts, similar to the corvette speed sensors, but maybe those were just sensors for ABS/TC.

Just curious.

nj02vette

iTrader: (2)

Bump.

Anyone???