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