How much of a dissertation do you want about the EGT? The instrument was developed by Al Hundre (? sp) of Alcor who make very good EGT instruments. It was made to solve a problem which showed up in the first turboprop engines. When a turboprop flames out the prop begins trying to motor the engine creating lots of drag in the process. This drag can be catastrophic to flight if it happens at a critical point in the flight. The purpose of the EGT was to sense the flameout and force the prop into feather without the pilots efforts.
The EGT used on a small Continental engine serves two purposes. It is very useful for diagnosing engine problems and it is a little bit useful for setting the mixture with the mixture control. When wired to all four cylinders the gauge will identify problem cylinders and settle your nerves on long flights when nothing is wrong. Mixture control works like this: At full power you want to be about 100 degrees richer than peak which is 25 to 50 degrees richer than best power. When the engine is working harder it is possible to cool it by using excess fuel which reduces combustion temperatures and improves the resistance to detonation. Best power which gives maximum speed is about 50 degrees richer than peak. You might think that maximum power would coincide with an ideal mixture but you get some more power from the expansion of the liquid fuel so a little extra is better. An ideal mixture should result in peak temperature because all the fuel is being converted to heat and for the most part this works out to be true with a few exceptions. Best economy is found on the lean side of peak but you do not have to be concerned about this in an Ercoupe as you will see. Operation of your engine is simple. Take-and climb below 5000' use a full rich mixture. Cruise below 5000' and above 60% power also use full rich. Below 60% power lean as you like. Cruise above 5000' can be as you like. In an unsupercharged engine the limit is set by the exhaust valves which don't like anything above 1600 degrees and prefer a 1500 degree limit. It is very difficult to reach these temperatures in the small Continental. Now for the gotchas. 1. The Stromberg works very well below 5000' . Leave it full rich and enjoy. 2. This will upset some on the list but here goes. When it comes to leaning the small Continentals you can do as well by ear and feel as you can by the gauge. These engines have a very poor mixture distribution so you are limited to leaning for the leanest cylinder and letting the rest run rich. You can do as well by pulling out the mixture control until the engine starts to run rough and push it back in to restore the smoothness. The larger fuel injected engines have better mixture distribution and can benefit from the gauge. A bit of trivia here: The reason you no longer see inline six cylinder engines in cars is that it is not possible to balance the distribution between the end and middle cylinders using one carburetor. There is no reasonable way to get them to pass the EPA requirements. 3. You cannot compare your results with anyone else's. Each installation is different as is each day with your engine. The gauge is wonderful for identifying problems and letting you know when there aren't any but it really isn't that effective on the Coupe engine for leaning. Bob Condon --------------------------------- to unsubscribe send mailto:[EMAIL PROTECTED] _____________________________________________________________ Check out the new and improved Topica site! http://www.topica.com/t/13
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