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What is a spark plug? It is simply a means of providing an electrical spark inside the combustion chamber. The plug however must seal against combustion chamber pressures, withstand contamination from fuels and oils and survive in an environment of extremes in temperature.

What does it do? Simply "lights the fire"

What does it need? Every spark plug must be surrounded by good compression; good air fuel mixture and good ignition or the plug will fail.

What is heat range?

It is the spark plugs ability to dissipate the combustion heat away from the centre electrode at the correct rate so that the electrode and insulator nose do not melt under extreme loads, while also retaining enough heat to burn off deposits at low speeds, idling or light throttle.

How is this done?

Heat range is designed into each spark plug by varying the length of the insulator nose. The longer the "nose" the more time it takes for combustion heat to travel up the insulator nose and out into the steel shell and cylinder head. Hence this is a "hot" plug - short insulator nose is a "cold" plug. Hot or cold plugs do not affect combustion temperatures.

If a spark plug shows signs of overheating (provided all other engine components are right) you would fit a "colder" plug - one with a shorter insulator nose which dissipates the heat more quickly. In NGK terminology low numbers (8) are "Hot", high numbers (10) are "Cold".

Hot Type

It has a larger surface exposed to the combustion gases. It dissipates heat slowly. Its firing end heats up quickly.

Cold Type

It has a smaller surface exposed to the combustion gases. It dissipates heat quickly. Its firing end does not heat up quickly.


These plugs have a very small centre electrode with a platinum tip. Platinum is a very hard material that can withstand extremely high temperatures and can dissipate the heat rapidly. These plugs offer the following advantages:

  • The very fine centre electrode allows the flame core to grow rapidly.
  • Has excellent ignition ability.
  • Fine electrode concentrates the electrostatic field resulting in lower voltage requirements.

Note: Can only be used with high quality unleaded fuels. Any trace of lead attacks the platinum resulting in shortened plug life.


Originally designed for two stroke motorcycles these plugs work exceptionally well. Palladium is a relatively soft material, but has excellent thermal characteristics advantages are:

  • High heat dissipation - ideal for race engines.
  • Ionise the immediate area requiring less ignition voltage.
  • Performs equally on any type of fuel.

Can withstand high thermal shock and has very good anti - fouling characteristics.

Note: B9EGV type plugs have a Gold Palladium Electrode and unfortunately they are being phased out. The suggested replacement type is B9EVX which has the Platinum Centre Electrode, this plug is more suited to Unleaded fuels