OK you  convinced me.  In light of what you just said what merit would
smaller  plugs have?
I was only interested in them because they would fit better in  a dual
plug insert.
Obviously a smaller plug means a smaller cavity in  the area near the
inner liner.  Is that such a
big deal.  For  instance when the leading apex seal crosses that hole is
there a transfer  of gases   from the presiding exhaust cycle?

Doug in  Japan



Doug,
The smaller cavity does both. It marginally improves compression and the
smaller opening has less gasses bypassing through it. A smaller plug gets the
actual spark closer to the combustion chamber as well.
Bill Jepson


Bill,

Thanks for your clarity and info.  I'll see what is availible in the
motorcycle world. I guess the Y type connection  you mentioned of
ignition implies two coils, and two ignitors for each plug and no wasted
spark.   Perhaps not needed for the trailing plugs.  That implies six
coils. I am wondering if one of the coils could be driven by a magneto
and the other by a CD system, or two CD systems to increase reliablity
since I have come to believe that the plug is not the weakest link. Your
thoughts are always welcome.

Doug in Japan