I received this from Dennis Hayes of Hayes Rotary in regards to
enlarging the trailing spark plug holes:

R.E. Enlarging Trailing Spark Plug Hole

I have 27 years experience working with the rotary engine, including
full dynamometer facilities in-house.  I am the largest remanufacturing
facility for rotary engines in the United States.  I have worked with
NASA, US Energy Dept., US Coast Guard.  I developed single rotary
applications for pumps and generators and I have worked extensively in
alternate fuel for the rotary engine which includes natural gas.
Over the past two decades for experimental aircraft only, I have
successfully opened up the trailing spark plug hole to allow for a TRUE
dual ignition system.  Dr. Michael Seals of Western Washington
University, who heads up the Vehicle Research Development Program for
the last three decades, and myself collaborated and developed the best
running and reliability redundancies of a TRUE dual ignition for
experimental aircraft.  We have built over 100 engines with this
modification.  We have disassembled and inspected engines after actual
aircraft usage and found no cracks in the spark plug holes, no pre
ignition, nor destruction of rotor housings.

Our findings were conclusive that there is certainly additional blow by
when the trailing spark plug hole is enlarged, specifically at idle and
low speeds.  Understandably aircraft application does not rely on idle
and low speeds for extended periods of time.  Dr. Michael Seals and
myself did not find any pre ignition conditions when running at higher
RPM.  After two decades of building experimental aircraft engine we have
not seen any destruction to a rotor housing.

The importance of this procedure is to have TRUE dual ignition systems,
allowing for enough engine power if  either the ignitions were to fail
to be able to land the vehicle safely.

Dr. Michael Seals and myself would recommend that if there is any
concern about enlarging the trailing spark plug hole, we suggest to have
a switch that if primary (leading) ignition were to fail you can turn on
the trailing ignition.

Without enlarging the trailing hole there will likely not be enough
power to land the vehicle safely.  We are troubled with the idea of
someone using dual ignition on the leading plugs only.  If a spark plug
fouls then there is no TRUE dual ignition.

Thank you
Dennis Hayes
Owner – Hayes Rotary Engineering