I have been reading the ignition information with some interest.
   The Plasma system didn't surprise me any with melting/burning off
   the tip, the insulator, etc.

   When the Toyota Tercel first came out (1979?), about half-way
   through that first the model year they had to change to use a
   dual gap plug. If one didn't use a dual gap plug, it would burn
   the adjustable electrode off (the one that is bent to allow an
   adjustable gap for "gapping" a plug for those who wondered what I
   was getting at).

   I believe it was Mazda had a 4 gap plug back in those days (we
   are talking 1979-83 or so).

   Given that the intake flow is at such a volume and velocity that
   we are seriously dealing with fluid dynamics, would having a
   "high energy" ignition with a dual gap plug work? And as I think
   about this, I think I understand why Mazda used a 4 gap plug --
   because one can't guarantee that the gaps would be placed
   correctly given the threads and torquing of the plug for sealing.
   So a 4 gap plug would possibly do better for that situation.

   Years earlier, Kawasaki used a plug with a center electrode and a
   concave metal plate that would allow the spark to jump around
   from point to point on the face. This was used in two-cycle
   185cc(?) dirt bike as I recall. It didn't like regular plugs
   (would burn off the electrode just like my Tercel did).

   Just trying to figure out how to get better performance with the
   rotary engine, possibly with off the shelf parts.

   Regards,
   Steve Thompson

   We use a single gap in the TTC set to .025 inches. No trouble at all.
   5 or 6 flights so far. It is a very cold racing plug.

   Paul Lamar


More likely Toyota changed heat range on the plug tip and the dual ground electrode was a bonus play.
Where combustion events are well controlled, plug tips do not tend to foul. So, extremely hot plugs are not required. Cooler plugs may be in an engine for many years causing no problems at all.
The four ground (Stock) Mazda plugs are a bit hot, so as to stay clean even at low speed but the four wide ground electrodes shield the insulator from direct contact with combustion temps and gasses at high throttle settings.  So in effect, two spark plug heat ranges in one plug.

In olden times, we used Champion N-57G gapped at .012". Thin wire center electrode in Gold Paladium.
Slightly hotter and cheaper was the Autolite AR-2592 with a cut back ground electrode. This is a cold NASCAR racing plug. Must order from any National auto parts store for overnight delivery. Works fine, very cheap. Once provided to racers by Mazda, NGK-R6725-11.5..........fine wire, retracted gap, Ice cold heat range. Will work with any ignition even the early points style Kettering system, but shine with killer ignition systems like the Mallory Hi fire or MSD. Gapped at .010"   Sadly about $30.00 each.

Lynn E. Hanover



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