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The Proper Spark Plug Gap

Spark Plugs Fire

For the better part of a century, automotive manufacturers have been transforming chemical and electrical energy into kinetic activity or motion. Your vehicle’s spark plugs supply the electrical energy. They typically fire thousands of times per minute, with x-millisecond bursts of energy. Arcs of sparks release between 20,000 and 50,000 volts of electricity, depending upon the design. The sparks rip apart compressed fuel molecules inside the cylinders. The expansions of the molecules power the motion and mechanical activities of your vehicle.

How is the Spark Generated?

An automotive ignition coil (or coils) is placed between the vehicle’s battery and spark plugs. The coil (or coils) take roughly 12 DC volts of electricity and transform it into tens of thousands of DC volts, as required by your vehicle’s specifications. The science behind the voltage increase and distribution is called electromagnetic induction, independently discovered in the first half of the nineteenth century by Michael Faraday and Joseph Henry. Simply illustrated:

  • An ignition coil is composed of ferrous plates wrapped by two sets of coiled conductors (copper wire), the primary and secondary windings.
  • The primary winding wraps around the ferrous plates. One side of the winding is connected to an interrupting switch that regulates the on/off flow of electrons from the battery to the coil. The opposite side of the winding is connected to ground.
  •  The opposite side of the winding is connected to ground. 
  • The secondary winding is wrapped around the primary winding. It can have as many as 100 wraps for every single wrap of the primary winding.
  • One side of the secondary is connected to ground, while the other eventually leads to the core conductor of your spark plug or plugs.

When the switch is closed on the primary conductor the coil creates a magnetic field. The electrons from the magnetic field encase both sets of windings. When the switch opens, or cycles to the off position, the magnetic field collapses and soaks the secondary winding with high voltage electrons. The electrons travel from the secondary winding through the spark plug core to the spark plug tip, where it arcs through the spark plug gap to the grounded side of the plug. This creates the desired electric spark of known duration and intensity.

Spark Plug Composition 

When it comes to constructing spark plugs - copper, platinum and iridium are the three metals of choice. Copper is a good conductor and many fine spark plug manufacturers use copper for the core conductor and ground elements. Copper, however, is the softest of the three, the most vulnerable to high pressure heat and the most susceptible to pitting, deformity and a decrease in longevity of performance. It’s also the least expensive. Platinum and iridium, on the other hand are one of the hardest and least corrosive metals mined and manufactured. 

Platinum and iridium are excellent conductors of electricity. Platinum can withstand 3,000 degrees of heat, plus, it’s a noble metal which means it’s resistant to change by other natural elements. Iridium, a derivative of platinum, is formed by treating platinum with nitric acid or hydrochloric acid. It too is among the most corrosive resistant conductors on the planet. It can withstand temperatures of 4,000 degrees Fahrenheit. Both platinum and iridium are a bit more expensive than the copper spark plugs, but under extreme conditions platinum and iridium hold up and perform better.

How Important is the Proper Spark Plug Gap?

It stands to reason that vehicles designed, engineered and manufactured to specifications require specific… well, specifications to operate at peak performance. Like the computer controlled timing and fuel mixture, or the pressure sensitive air flow, the spark plug gap between the conductor and ground is formulated for overall operating efficiency and effectiveness at varying degrees of temperature and specific pounds per square inch of compression. The angle at which the spark plug ground faces the conductor will influence the purity of the arc, the uniformity of wear and the resistance / susceptibility of carbon deposits. For these reasons - the next time you replace your spark plugs, check the alignment and space the gap according to the specifications with the proper spark plug gapping tool for the job.


The next time you replace your spark plugs, check the alignment and space the gap according to the specifications with the proper spark plug gapping tool for the job.

The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician. We encourage you to consult with a certified technician if you have specific questions or concerns relating to any of the topics covered herein.

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