Twin-cylinder four-stroke air-cooled rebirth of a Ducati 500SL







At the moment the spark jumps the Gap it causes a high frequency burst of energy, known as RFI (radio frequency interference). RFI, as its name suggests, creates static on your radio and interference with other electronic equipment, including the vehicle’s on-board electronic control units (ECUs).


Resistor plugs were developed in the 1960s to suppress some of the spark energy, thus lowering RFI to an acceptable level.  Most Resistorspark plugs use a monolithic Resistor, generally made of graphite and
glass materials, to filter the electrical voltage as it passes through theCenter Electrode.


Since Resistor type plugs actually “resist” some of the spark energy, non-Resistor type plugs actually deliver a more powerful spark.  It is for this reason that most racing plugs are non-Resistor types.  However, in most automotive applications, a Resistor plug is required for proper vehicle operation.  Use of non-Resistor plugs in
vehicles that call for a Resistor type can result in rough idling, high-rpm misfire, and abnormal combustion.