dr_gallup said:
Every once in a while I have found an engine that hated a particular style of plug but I have never found a magic plug that performed way better than anything else.
I have, but it is not available in a 10mm thread - only 14mm. Bosch makes a modified surface gap racing plug that has made more power in every engine I have tested them in, from 540ci Chevies, to two-stroke engines. They are commonly used in F1, NASCAR, and several other forms of racing - all with very good results. You ought to see the way it acts in a pressure chamber, and the burn patern results on the top of pistons - very impressive spark kernal that initiates a much larger burn pattern.
On your old Rickman, did you ever try the Champion "power gap" plugs? Magnetos seem to love them, too bad they are no longer available.
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Bosch F09DER modified surface gap.
Notice hand cut threads and side/surface gap electrodes.
Don't bother trying to ask the local plug supplier about them, "they don't exist" is the normal reply.