200 Quattro Wagon L5-2226cc 2.22L SOHC Turbo (MC) (1989)
Spark Plug: Description and Operation
The spark plugs protrude into the combustion chambers and provide the spark that ignites the compressed air/fuel mixture. There are many different
types of spark plugs for the many different applications and each type has specific advantages for its applications. Different features include:
Typical Spark Plug Construction
1.
THREAD SIZE - The diameter and pitch of the threaded portion of the spark plug.
2.
REACH - The length of the threaded portion and how far the electrode protrudes into the combustion chamber.
Spark Plug Heat Range Illustrated
3.
HEAT RANGE - The ability of the spark plug to cool its electrodes.
a. Hot plugs have longer insulators around the center electrode and less cross-sectional area for heat to transfer from the electrode to the
cylinder head. Heat is conducted away from the center electrode more slowly and the electrode tip stays at a higher operating temperature.
b. Cold plugs have shorter insulators around the center electrode and a larger cross-sectional area for heat to transfer to the cylinder head. Heat
is conducted away from the center electrode quickly and the electrode remains at a cooler operating temperature.
4.
RESISTOR TYPE - Most spark plugs are resistor type plugs. These have a carbon resistor or auxiliary air gap built into them to provide radio
static suppression and to ensure a higher sparking voltage is reached in the secondary ignition circuit before the spark occurs. Resistor type spark
plugs are always used with high energy electronic ignition systems.