As I recall people say loss of the top plug has little effect
 on power. IMHO it was done for emissions primarily.

 The dual side by side plugs have little effect on the BSFC
 as those that have them show no advantage. On the other hand they are
 either air cooled rotors or charged cooled rotor engines so it is not
 a real back to back test.

 Paul Lamar

 Paul,
 I would logically conclude the twined leading plugs are simply for standard
 redundancy.BTW Mazda terms, lower plug LEADING, higher plug TRAILING. This was a
 bit confusing to me at first. To answer Skip, I wouldn't want either plug failing
 since you lose power either way.One answer for that is redundant COILS on the
 same plug.You can get a'Y' to tee two coils into one plug. Electronics is the
 likely failure, so I would feel safe with a single leading plug personally.I
 will have 3 rotors though soI could probably limp home on2+20%. The single
 rotor guys might have more to say about this. We aren't drag racers here
 though. Once run for a while, say 20 hours, you have passed infant mortality
 and if your temps are under control you will probably run for years. That is
 why the FAA has the 40 hour fly off mark to begin with. Most of us won't even be
 asking our engines to develop full automotive level HP! My 20B will be loafing to
 produce the 250-260 HP max recommended for my RV-10. The twin turbo cosmo made 345
 HP stock. I am not going out on a limb thinking that factors other than the
 engine itself will be my likely failure modes. Paul has beating this into the
 ground but it is true none the less, design your external systems carefully and
 the rotary won't let you down.
 Bill Jepson


 If you fired the plug with 4 sparks .2 ms long 1 ms apart might be the same
 effect on the plugs as one inductive spark 1 ms long.

 I re read K.Y.'s book on the subject and there is little advantage to the
 upper plug. What they published was BMEP data at only several lean mixture
 settings. No BSFC data.

 I think two lower plugs side by side are not worth it. Too risky! Could damage
 the rotor housing but I have no objection to it if you are going
 to carefully measure the BSFC change (if any) on a good dyno.

 IMHO your better off spending your time and money on TC.
 BTW how is that coming

 Paul Lamar

   The top (trailing) plug does actually have an effect on power, a negative one.
 The top plug was installed from the factory in order to reduce BSFC but at the
 cost of charge efficiency (HP) due to increased blow back. Looking at the
 graphs that are posted in the 1981 K.Y. Rotary Engine book, both HC and NOx
 emissions where increased when the top (trailing) plug was added so I conclude
 that it was NOT added for emissions reasons. As far as actual change, the 1981
 book shows ~10 g/ps-h decrease of BSFC. I know I'm a day late and a dollar
 short, but whatever. Thought I'd add some fuel to the fire. Cheers.
 Vlad


OK, now I'm totally lost.  The top plug reduces power and increases
emissions.  So what does it do!  In other words, what positive effect
caused Mazda to put it in.

Bob W.