A non-wasted spark system only provides a spark on the compression cycle of each cylinder of a four-stroke engine. Each cylinder requires an ignition coil, and the timing disk for the ignition system needs to rotate at half engine speed (cam shaft speed).
A wasted spark system produces a spark for the compression and exhaust stroke of each cylinder in a four-stroke engine. The reason this system is called wasted spark is that only the spark on the compression cycle is useful, the spark on the exhaust stroke is ‘wasted' as there is no combustible mixture in the cylinder.
Depending on the engine configuration it may be possible to use one dual-output ignition coil to operate two cylinders in wasted spark mode. A benefit of wasted spark systems is that the timing disk is attached to the crankshaft, which is generally more accessible.
Wasted spark ignition systems are commonly found in motorcycles but are not recommended for use in industrial or alternative fuelled applications.
