Originally Posted by ppayer38
RomRaider lags back around 150-200 rpm as you have to give time for the data to transfer from ECU to laptop. This has been focussed before if you would have searched. The tach is a calculated measurment made by the ECU, etc.
Electrons do not work that way!
The O2 sensors lag slightly depending on position because it takes a little bit for the exhaust gasses to move. The crank trigger has to be extremely precise to deliver fuel and spark on time and that is where RPM comes from. The data to romraider is just a snapshot taken of the values several times per second.
The tach is just an approximation for the driver to use, DO NOT trust it over the values you are programming into the ECU.