The Modular ECUs have a dedicated tacho output pin. This pin is intended for use only as a tachometer function, and can’t be used for generic outputs or engine synchronous functions.



There is a small inductor built into the ECU to generate a small amount of flyback voltage to simulate an ignition coil, for factory tachometers that require such a signal. So the output is internally pull-ed up to 12V and no external pullup resistor is required.

The only setting that’s required, and this can be found in the functions -> Tacho part in the software, is the output frequency. In the cast majority of cars, the tacho output frequency is the same as the ignition frequency, for example on a 4 cylinder or a 2-rotor engine, the tacho will have two pulses per crank revolution, and an 8 cylinder will have 4 pulses per crank revolution. We give the option in the software to select a different output frequency for cars where this is not the case, and the case of engine conversions.

If you leave this setting set to “standard”, then it will calculate the frequency based on the ignition output frequency (ie, based on the RPM, the number of cylinders and the firing frequency, ie every 360 or every 720 degrees). Otherwise you can choose the number of cylinders to simulate. For example if you choose a 2 cylinder engine, you will have a tacho pulse every 360 degrees.

So, if you were installing a JZ or an RB engine into a Silvia chassis and retaining the factory instrument cluster, you could set the tacho frequency to be 4 cylinder and it would read correctly.

Again note that the tacho output is a variable frequency, and it’s not phase locked to the engine’s rotation.

	3000 RPM	6000 RPM	9000 RPM
1 cylinder	25 Hz	50 Hz	75 Hz
2 cylinder	50 Hz	100 Hz	150 Hz
3 cylinder	75 Hz	150 Hz	225 Hz
4 cylinder	100 Hz	200 Hz	300 Hz
5 cylinder	125 Hz	250 Hz	375 Hz
6 cylinder	150 Hz	300 Hz	450 Hz
7 cylinder	175 Hz	350 Hz	525 Hz
8 cylinder	200 Hz	400 Hz	600 Hz
9 cylinder	225 Hz	450 Hz	675 Hz
10 cylinder	250 Hz	500 Hz	750 Hz
11 cylinder	275 Hz	550 Hz	825 Hz
12 cylinder	300 Hz	600 Hz	900 Hz
13 cylinder	325 Hz	650 Hz	975 Hz
14 cylinder	350 Hz	700 Hz	1050 Hz
15 cylinder	375 Hz	750 Hz	1125 Hz
16 cylinder	400 Hz	800 Hz	1200 Hz

Thanks and happy learning!