Indexing spark plugs is a fairly simple way to increase your vehicle’s power and performance. For years, race car drivers have been using the technique to gain optimal efficiency from each cylinder, as well as sustaining consistent combustion throughout. The main goal of indexing is to ensure that each spark plug’s ground electrode is correctly positioned so that it’s not blocking any portion of the spark as it moves from the plug into the chamber. One of the pitfalls of mass-produced parts like plugs and cylinder heads is that there’s no absolute guarantee of the perfect fit. Plug in and jam
So, how should spark plugs be positioned? The plug’s gap should be facing towards the valves so that the spark has full access to—and is aimed towards—the center of the combustion chamber.
Have pen will travel
Indexing your plugs is easy, just grab a felt-tip marker and mark the exact location of the gap on the corresponding part of the outside plug. When you install it, make note of the direction the mark faces. If you need to further adjust, you can also add an appropriate-sized indexing washer (copper is best) to change the orientation of the plug, so that when tightened, the mark you’ve made is facing in the correct position, in conjunction with the combustion chamber.
Onward we go
Indexing will only work on conventional gapped plugs with a grounding that extends from the threaded area. There are newer styles that are self-indexing, with either multiple electrodes, or no exterior grounding electrode extending from the threaded bushing at all. The cost of these more highly evolved spark plugs is substantially higher than standard plugs.As you explore ways to maximize performance, check out these different spark plug options.