The Mazda rotary runs very well on the leading ignition only.
The engine makes far more torque without the trailing ignition.
For years I sold a aluminum plug that went into the trailing
spark plug hole. It was to eliminate detonation. This worked
perfectly to do that. This also made it possible to run 87 octane
fuel on turbo RX7's. Still sell the device today for auto use.
Most of the rotary auto shops incorporate this method when dyno
tuning turbo rotary cars. The mazda engine will not keep the
airplane flying on just the trailing ignition.The engine will
stay running but not make the power to maintain flight. The
trailing ignition is for automobile emissions only.

What I have done for aircraft is modify the rotor housing by
welding up the trailing spark plug hole and the leading hole.
Then machine two side by side spark plug holes below the minor
axis. Now you have a true back up ignition. There is a 50 rpm
drop on preflight run up test at idle but no drop in rpm at
full and cruise power settings.

Skip Gorman

Do you have any dyno curves or pictures of your modifications
to prove these contentions? These results are at odds with
Kenichi Yamamoto's book Rotary Engine. See the attached
screen capture. An increase in Mean effective
Pressure is an increase in torque and HP.


Paul Lamar

What is "excess air ratio"?

It seems to be implying there is more "excess air" when the combustion
is better.

Bob W.