RacingTach is a tachometer using the sound or any periodic signal coming from engines. It can measure precisely the RPM up to 100 000 of race cars, motorbikes, trucks, motorboats, R/C models but it can also use the sound of plane's propeller, helicopter's blades etc... The signal is analyzed in real time using a proprietary FFT algorithm which is one of the fastest implementations.

Settings of the application

    ‘Events per revolution'

    It is the number of pulses seen by the software when the crankshaft of the engine performs one revolution. You need to know that if your combustion engine is a four-stroke engine : there are two crankshaft rotations per working cycle or if it is a two-stroke engine : there is one crankshaft rotation.

    So with the microphone or with a cigarette lighter RPM pickup, the formula for determining how many times your engine fires per revolution is :

    • 0.5 X the number of cylinders for a four-stroke engine
    • 1 X the number of cylinders for a two-stroke engine.

    Examples :

    • Four-stroke & 4 cylinders engine => 0.5 * 4 = 2 sparks per revolution (the common value for a car)
    • Four-stroke & 6 cylinders engine => 0.5 * 6 = 3 sparks per revolution
    • Two-stroke & 2 cylinders engine => 1 * 2 = 2 sparks per revolution

    If you use an inductive clamp around one spark plug wire, the application sees only the pulse from this wire therefore the ‘Events per revolution’ parameter is 0.5 for a four-stroke and 1 for a two-stroke engine.

    'Min RPM' and 'Max RPM'

    You can adjust these settings according to your engine capacity in order to improve the reliability of the RPM.

    'Peak threshold research (%)'

    Use this parameter to adjust the threshold of the tracking of the RPM frequency peak. Try to keep the value as high as possible but decrease it if one of the harmonic peak of the RPM signal is often higher than his fundamental frequency.

    'Shift light alarm (RPM)'

    It is the minimum value of the RPM before the alarm occurs (ie the background screen of the tachometer blinks). For example, in a race car with manual transmission a driver can use it to know when he needs to shift up a gear.

    'Shift light sound'

    Set to ON only if you have an external microphone far from your iphone / ipod speaker or if you have inductive / cigarette lighter RPM pickup otherwise the alarm sound may disturb the RPM measurement.

For advanced users

    If the sound of the engine is too masked by other noises or if you want to get a more reliable measure you can use :

    • An external microphone around the cat back exhaust of your car or motorbike
    • An inductive clamp (pickup) around one of the spark plug wires. It is the best solution for gasoline engine. You can buy one here
    • A cigarette lighter RPM pickup which extracts engine RPM from inductive (“ignition noise”) pulses induced into the vehicle’s 12-volt wiring by the spark-plug coil’s firing (Warning : it can be affected by radiator cooling fan, air-conditioner, car radio, car navigation ...)

      Here you will find an electronic circuit diagram :

      You will need a 4 Conductor 3.5mm Plug like this. It would be useful to build a splitter Adapter Mic/Headphone Converter Cable like this or this


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