The timing problem is no problem at all. All references to timing are in crankshaft degrees and the crankshaft is turning  three times faster than the rotor. So start thinking in terms of 1/3 of whatever timing is recommended for a rotary. Then compare that to your automotive experience. The engine will start and run just fine on nearly any timing number you can think of. For emissions control the rotary has come with timing like 5 BTDC and a split of 8 ATDC. A very modest 20 BTDC both is what was used for years in racing and off road and good up to 9,000 RPM. The lower the fuel octane the better the engine runs.

 

For using avgas with slightly lower flame front speeds a bit more timing should be dialed in for good milage.

For constant RPM operation 24 -28 degrees would work well. Even then the timing at the rotor face is a very mild 8 degrees BTDC. 

 

The secondary (high voltage) ignition breakdown was for more typical of points ignitions in the past. Points open slowly and with much electrical noise. Each cycle is different from the last. Slow switching a Kettering system allows slow voltage build up on the plug. So a number of viable paths may charge up before the primary collapse is complete. This flow is subtracted from the maximum secondary voltage expected at the plug gap. Later, electronic switching of Kettering systems eliminates this problem.

 

So we are left with the "SAG" being caused by plug fouling providing dual paths for secondary flow, the lead fowling or the electrode gap. Voltage demand at the gap goes up with cylinder pressure. High cylinder pressure occurs at full throttle. So, if a slight throttle reduction (lowers cylinder pressure) eliminates the problem, it is likely that fouling is the culprit. If caught away from support, a reduction in plug gap will perk things up for a while. In the race car I use two MSD 6ALs with rev limiter chips for 9,800 RPM and NGK R6725-115 gapped at .010". Too cold a range for aircraft use and very expensive, but the gap is about right for very high RPM use.

 

Lynn E. Hanover 

 

 

 

 

 

In a message dated 4/28/2008 5:07:59 AM Pacific Daylight Time, eanderson@carolina.rr.com writes: