Resistance in spark plugs was originally added to control electromagnetic interferance, EMI. With the introduction of television, there was a continual disturbance of television reception with vehicles producing EMI from the sparking of the spark plugs. To reduce EMI, spark plug wires went resistive, and resistance was inserted in the spark plug construction. To the automotive connoiseur, this was interpreted to produce a weaker spark, and a decrease in power.
However, being that the average person has not studied electrical theory, the spark plug resistance effect is not well understood. Firstly, the current through the spark plug is small, in the order of micro amperes in today’s engines. What must be considered is the effect of the spark plug ignition coil. Spark Plug Ignition Coils are high voltage transformers which contain thousands of turns of wire with very high resistance coil wire. In its connection to a spark plug with no resistance, and low resistance in the connecting ignition wire, when the spark plug is sparked, the effective resistance across the spark plug gap is zero. And the spark power is primarily lost in the high resistance of the coil. Also, this can result in a burn out of the ignition coil. With resistance added to the spark plug, there is protection of the ignition coil from burn out.
For optimum power delivered to the spark plug, there should be a balance of resistance between the spark plug coil, and the spark plug resistance, In practice, the resistance should be approximately 5,000 ohms. The resistance is not super critical. But, spark plug resistances will vary, Greater than 10,000 ohms, the effect can result in effective power loss to the spark plug. The point is that the power to the spark plug consists of two components namely voltage and current. The voltage arrives first, and then is followed by the current. Excessive resistance will delay the arival of the current. Technically, this is a phase delay which decreases the effective spark power.
Posts