of my 24 tooth wheel i can see crank speed variations as much as close to 500 rpm 3 times pr crank revolution. The crank speeds up every time a cylinder fires and slows down in between. (kinda makes you realize why they make harmonic balancers). Now the ecu average these variations out for its RPM parameter. But im just saying... Im using that to see if all my cylinders are doing its share of work or not.