After spending many years building and tuning air cooled, low rpm, high torque Harley Davidson engines, I am now into experimental air cooled, low rpm, high torque aircraft engines.  I have been watching EAA seminars presented by Mike Bush (Savvy Aviation) on You Tube and he generously is presenting his lifetime knowledge of maintaining and tuning piston engines.  He has a presentation covering EGT and CHT and it has really enlightened me regarding how to interpret the readings for engine operation and maintenance.  The big shocker for me was that EGT measurements are about useless for engine operation but are very useful for diagnosing engine issues.

http://www.youtube.com/watch?v=fqe9j74qMdk

I have attached the link as I think others will find it very informative.  I have noticed that pilots spend a lot of time chasing EGT readings and misinterpreting them ie a high EGT means that the engiine is running to hot (which is usually just the opposite) when in fact, the EGT gauge is displaying only a relative value, not an absolute value.  According to Mike, the CHT needs to be monitored during operation, not the EGT.  Only when the engine is not performing normally can you use the EGT to help diagnose the issue.

I believe he has presented over 150 webinars for EAA regarding piston engines.   

I have a 1st generation Jabiru 3300 which I recently aquired and his videos have really pointed me in the right direction on how to manage this engine. 

I was thinking maybe others would find his information helpful.

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Good timing.  I'm about to dive down that rabbit hole so any information is appreciated.  I'll watch this tonight.

You are spot-on! Years ago, I heard one of Mike's seminars on EGT/CHT and it made sense then and it makes sense now! There are so many variables that affect EGT's that they certainly don't represent absolute values!  I'm much more concerned with CHT's and definitely think you should have 6 probe CHT monitoring on the 3300!

John

N750A

Thanks John,

   I certainly plan to watch all of Mike Bush's webinars.  He has several good ones regarding cylinders and exhaust valves that are real eye opening.  I didn't realize  how nasty the side affects of 100LL fuel are on exhaust valves.  I have read reports that Jabiru exhaust valves stick and can't help but think that 100LL was the sole contributor to the problem.  I know that just like Rotax, Jabiru engines are not designed to use 100LL although they can but user beware.  I don't believe Jabirus have the rotating exhaust valve caps that Lycomings and Continentals have to mitigate the fouling effects of 100LL on exhaust valve stems.  I would love to hear about Jabiru owners experiences using 100LL over several hundred hours of operations. 

I only run 100LL when forced to such as on a long cross-country, otherwise I run 93 unleaded/no ethanol and it works great.  I'm very fortunate to have a gas station nearby that has all grades of "pure" gas/no ethanol!

John

Another Relevent presentation by Mike Bush regarding EGT

"The EGT Myth" webinar for the EAA

https://www.youtube.com/watch?v=VvxeEQC-7p8&t=3077s

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