Direct C51 wrote:Wes, I want to show you a picture of the data log on my engine so that you can really understand that absolute EGT values mean NOTHING.
Going by absolute EGT, you would think my #5 cylinder (Lowest EGT) is really rich, and #3 and #4 (Highest EGTs) are really lean. But that is opposite of true. #5 peaks well before #3 and #4, indicating that it is actually a much leaner cylinder. I have a 72 degree spread between the highest and lowest peak EGT. Do you know what that means? NOTHING! It means absolutely nothing. In fact, I don't even fly around with the actual EGT numbers displayed in cruise. My EFIS has a setting that will show how many degrees from peak you are. See the second picture, this is how I fly. Degrees away from peak means something. Absolute EGT value does not.
By the statements contained above as well as those contained within your earlier messages with regards to absolute EGT values, it appears that you have accepted the Mike Busch concept of "mixture" theory that he applies to Continental and Lycoming engines as being applicable to your Jabiru 3300 engine as well. I'm not convinced that this is a good idea. The Jabiru factory is quite clear in providing absolute EGT values that are not to be exceeded for various power settings. Why? Because running a Jabiru exhaust valve at too high of an absolute EGT value for too long of a period of time has shown to contribute to the developmen of transverse hairline cracks in the valve stems and, ultimately, their failure. Roger Lewis of Power Engineering Consultancy, a prominent Jabiru engine expert in Europe, has in the past verified this phenomenon in the many engines he has torn down. He strongly recommends checking for valve stem cracks whenever an engine is opened up and especially if the engine has been operated with excessively high absolute EGT values in the past.
More than just my opinion,
Art,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,Jabiru 3300 #261