Editing Spark plug (section)

==Indexing spark plugs==
"Indexing" of plugs upon installation involves installing the spark plug so that the open area of its gap, not shrouded by the ground electrode, faces the center of the combustion chamber rather than one of its walls. The theory holds that this will maximize the exposure of the fuel-air mixture to the spark, also ensuring that every combustion chamber is even in layout and therefore resulting in better ignition. Indexing is accomplished by marking the location of the gap on the outside of the plug, installing it, and noting the direction in which the mark faces. Then the plug is removed and washers are added to change the orientation of the tightened plug. This must be done individually for each plug, as the orientation of the gap with respect to the threads of the shell is [[random]]. Some plugs are made with a non-random orientation of the gap and are usually marked as such by a suffix to the model number; typically these are specified by manufacturers of very small engines where the spark plug tip and electrodes form a significantly large part of the shape of the combustion chamber. The [[Honda Insight]] has indexed spark plugs from factory, with four different part numbers available corresponding to the different degrees of indexing to achieve most efficient combustion and maximal fuel efficiency.{{CN|date=September 2017}}