Spark Plug Indexing

In attempting to squeeze out that last bit of potential output from the Ford Y-Block (and other engines), there are those items that can be applied that may not be immediately measurable but they will be done because they will not be detrimental to the power output.  One of these items is spark plug indexing which tends to vary in its benefit depending upon the application it is being applied.  Indexing the spark plugs simply insures that the spark plug ground electrode is in a specific orientation within the cylinder to promote a more beneficial flame front when the fuel is ignited.  In those cases where detonation is a risk, spark plug indexing is of a proven benefit in that the flame front will not be split by a worst case scenario of the spark plug electrode being in a position to divide the flame path.  Indexing also allows the ground electrode or strap to be intentionally positioned away from the higher heat areas it would be subjected to if randomly placed closer to the piston and/or exhaust valve which can increase the propensity for pre-ignition.  In a normal situation where a set of spark plugs are randomly installed, the spark plug straps end up running at a variety of temperatures simply from the random placements of the straps.  In this case, indexing would provide a more accurate visual means towards optimizing jetting and ignition timing by eliminating potential variances in the spark plug readings themselves.  And if running a domed piston that’s marginally close to the spark plug, then indexing also helps in preventing the ground electrode from contacting the piston and potentially closing the gap.
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