Innovate Motorsports LM-1 RPM Converter (Aux. Input Cable 2) - Manual (Page 4)

2.2 Two-Stroke Engines
On a 2-stroke engine there is a spark for every crank rotation, so the spark frequency doubles
compared to a 4-stroke.Very few multi-cylinder 2-strokes have distributors. For those that do, the
number of ignition pulses per crank rotation is equal to the number of cylinders. Most two-stroke
engines have one coil for every cylinder. The coil fires once for every crank revolution, the same
as on a 4-Stroke Waste Spark system.
2.3 Rotary Engines (Wankel Motors)
A rotary engine consists of a roughly triangle shaped rotor rotating in a roughly elliptical chamber.
The three spaces left between the chamber and the rotor go through the four cycles of a four-
stroke engine for each rotation of the rotor. A single (or dual) spark plug at a fixed position in the
chamber ignites the mixture of each space in sequence. Therefore, a rotary engine requires 3
sparks for every rotation of the rotor. The mechanical power from the rotor is coupled to an
eccentric gear to the output shaft. This gear has a 3:1 gear ratio and the output shaft therefore
rotates 3 times faster than the rotor. The output shaft is the equivalent of the crankshaft on a
piston engine. Because RPMs are measured conventionally as the rotations of the crankshaft,
the rotary engine requires one spark for every 'crankshaft' rotation, the same as a two-stroke
engine.
3. Using the RPM-Converter with the Inductive Clamp
The inductive clamp measures the magnetic field created around a spark plug wire when spark
current flows. If a metallic shield covers the spark plug wire, the inductive clamp may not work
because the shield would short out the magnetic field. Like all inductive clamp rpm pickup
devices, some ignition systems like Capacitive Discharge Ignition (CDI) or multi-spark ignition
systems may not work properly with the inductive clamp pickup because the pulses created may
be too short in duration. Multi-spark systems confuse the ignition timing measurement because
the RPM converter cannot distinguish which ignition pulse belongs to which crank rotation. The
RPM converter will work only on the tach output of the ignition system in this case.
The inductive clamp must be clamped around ONE lead only. Clamping it (for example)
around all wires of a coil-on-plug pack does not allow it to work because the magnetic
fields of the wires most likely cancel each other out.