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You can install the Spark Plugs while making sure the electrode is pointing a certain direction, and pickup up fractional HP.
Overview
The idea of indexing is to direct the spark towards the inlet of air/fuel this can create a better fire in the chamber. If plugs are not indexed the electrode can theoretically shield the spark as a worst case scenario.
Indexing is not a problem with the A-series combustion chamber. Still, every bit helps, right?
Draw a line on the hex visible to the outside, in line with the electrode. Use different thicknesses of seals if it doesn't line up.
Install them so that the open area of the spark gap, not shrouded by the ground electrode, faces the center of the combustion chamber, towards the intake valve, rather than the wall.
After installing a plug, note the direction in which the mark faces. If needed remove the plug and fit additional washers so as 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.