I currently have an open diff which I think is a 3.23. I rotated one wheel and counted exactly 21 shaft revs to exactly 13 wheel revs. If I change to a 3.27 will I need a new speed sensor to keep the engine running correctly or is the ratio close enough to not need it? I calculate the 3.27 will turn the wheel 12.84 revs instead of 13. Doesn't seem like a lot but I've never done it before with computer control. How much can you change before needing to swap the VSS?

 

Won't affect much in the ECM, not enough of a change. 3.27 / 3.23 = 1.2% difference. The ECM will think that the car is moving 1.2% faster then it really is. So the speed limiter will kick in at 114 MPH instead of 115 MPH. TCC will lock up a smidge sooner, and so on.

In the stickys of the transmission board should be a thread on the transmission driven and drive gears. Along with how to calculate which ones are required. It isn't the VSS that gets changed, just a gear or two that drives the VSS.

RBob.