Lynn would be the one to address what -  if any -  effects opening up the trailing spark plug hole would have.  I must admit I would be a bit concerned about flash over into the next rotor face as its coming up on its compression stroke, but that is purely speculation on my part - don't know if it even could happen.. 

 

Ed

The trailing (little hole) is there for two reasons. It helps the very long combustion chamber and allows for a very long period to burn close to all of the mixture. There are folks who drill out the trailing hole to get a faster burn going.

 

Probably never a problem so long as the timing is moderate and idle speed is high enough. Should burning mixture cross over that drilled out hole and ignite the next chamber, the engine will not survive the event.

(it shears off the top dowel) The little hole also allows for a shielded plug to survive a flooding situation, and still start the engine.

 

The Aussies drill that hole slightly bigger, and machine a lateral groove, about 3/4" across the hole. It is alleged that this would get the better burn of the big hole without the pre-ignition danger.

 

I can see the loss of the trailing ignition system in the lap times. The driver cannot feel the difference. The driver reporting a soft engine should he ever look at a gage, would mean a leading ignition failure, or about a 5% loss of power. The EGT goes up because slightly less fuel is burning inside the chamber, and more is burning around the probes.

 

In either case, the loss of one system is a non event. Just like a real airplane engine but better.

 

At aircraft RPM, the burn rates are plenty fast enough to get it all done on one plug, so the power difference for ignition problems is minimal. The bigger the timing split, the more obvious will be the loss of the leading system. None is used in racing. After about 2500 RPM, it is of little value except for emissions.

 

 

Lynn E. Hanover