While no two installations are identical, here some ideas that have worked for me and my thinking on why.

 

EGT (Exhaust Gas Temperature) is a view inside the combustion chamber with an eye toward performance.

 

EGT probes go in the header pipe 3" out from the port face. If the pipe is curving this close to the engine, the probe goes on the outside of the curve. Exhaust gasses are passing over the probe above the speed of sound. How hot or cold the pipe is will be of no matter.  There is no time for cooling losses.

 

The idea of the EGT monitoring is to keep the mixture well rich of PEAK EGT. Because you can melt important pieces at 1900 Degrees. So we run the engine rich of best power and well rich of peak EGT.

 

The muffler and Apex seals will thank you.

 

At best power the EGT is just a blink rich of peak EGT. So the story about the engine running real strong just before it melted a piston, is accurate. It was running at best power and melted a piston.

 

Another old saw is: I leaned it out just one jet size and it melted a piston. Again accurate. The engine was running just rich enough to stay alive (just rich of best power) and leaning the engine took it to best power or just a bit worse (Peak EGT). 

 

The cast iron rotor will not melt but the apex seals can warp from overheated centers passing over the exhaust port.

 

So shoot for About 12.5:1 on the A/F meter or 1600 degrees or less on the EGT for take off, climb and accelerate to cruise speed. Then quickly lean past peak EGT to lean stumble, then back rich just enough for smooth operation. Check the EGT now. If you want even more range add a monster ignition system and you can hold off lean stumble while going even leaner. Control power with fuel flow. Leave the throttle wide open.

 

 The EGT gage only works for loaded wide open throttle operation. It is useless otherwise. A heated O2 sensor for other work.

 

In the search for more power we often leave out oil cooling. More important on Pported engines than side ported. The poorly cooled rotor (Oil cooled) can see the inlet tract in Infr-red. In the Pport nearly all of it can be seen. So the inlet charge is heated before it gets into the engine. Remember pulling on the carb heat on the Cub and looking for a 150 RPM drop? Same idea. Charge expands so less fuel and air per cubic foot so less power. Simple. In the side port engine not much of the inlet can be "seen" by the rotor, so a bit less effect.

 

This applies to older side port and Pport engines. Renesis and turbocharged engines are completely different and require different support.

 

Mistral was probably running as lean as is possible without damage. That would be rich of peak for full throttle, and less rich for cruise. They had to stay on the safe side of everything, as they had no control of the installations (I was offered a job inspecting Mistral customer installations) and no control of fuel octane or quality. No doubt there are knock sensors in their system, but I know nothing of how it works.

 

There is much more......................

 

Lynn E. Hanover