CHT vs EGT

[BearP]

I have a Lycomming 360 M1-A and cannot find what the EGT settings would be relative to the CHT settings.

So my question is: When leaning an engine out my CHT is about 400 and my EGT is about 1500. Where can I find the correlations & Mid/Max's for a variety of settings

Thanks

 

[Ted]

There is no such curve. EGT is primarily a function of your manifold pressure, RPM, and mixture setting. CHT is a function of those, but also of cooling. As the cooling over your engine is variable dependent on a number of factors (altitude, airspeed, outside air temperature, cowl flap setting, etc.).

Lycoming Service Instruction 1094D provides a bit more information on leaning procedures, and additionally states:

For maximum service life, maintain the following recommended limits for continuous cruise operation:

Cylinder Head Temperature: 400F or less

http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1094D.pdf

 

[Bob Noel]

EGT is also a function of where the probe is, that is, how far down the pipe the probe is installed.

 

[Ted]

EGT is also a function of where the probe is, that is, how far down the pipe the probe is installed.

Also true, as well as depth of the probe in the exhaust pipe.

 

[John Collins]

In a sense, EGT is not the real temperature of the exhaust gases that come out of the cylinder, they are much higher. Assuming a probe a few inches down the exhaust pipe, the gasses have had ample time to cool. Further more, the exhaust gasses only pass the probe while the exhaust valve is open, so much of the time, the probe is cooling itself. What you see is an average temperature of the probe, with the probe cooling during most of the engine cycle. In most instances, the actual value of the EGT is not relevant. What is relevant, is the temperature measured differentially with respect to the peak temperature of the probe.

 

[Ted]

In most instances, the actual value of the EGT is not relevant. What is relevant, is the temperature measured differentially with respect to the peak temperature of the probe.

This varies heavily from engine to engine. On most naturally aspirated aircraft (especially training aircraft), that is correct. However EGT/TIT raw values are quite important on higher powered engines, especially turbocharged. The temperature that the metal sees (and heats up to) is important.

 

[John Collins]

This varies heavily from engine to engine. On most naturally aspirated aircraft (especially training aircraft), that is correct. However EGT/TIT raw values are quite important on higher powered engines, especially turbocharged. The temperature that the metal sees (and heats up to) is important.

I have seen operating limits on TIT for turbocharged engines, but have not come across any operating limits for EGT. Do you have an engine and a EGT limit in mind?

 

[Ted]

I have seen operating limits on TIT for turbocharged engines, but have not come across any operating limits for EGT. Do you have an engine and a EGT limit in mind?

That part is true, I can't think of any naturally aspirated engines that have an EGT limit. In that case, I typically look at TIT limits for most turbo engines and figure that if a turbocharged engine shouldn't operate there (granted, that is a turbocharger limit), the exhaust system on my naturally aspirated engine probably won't like it, either. The 520s on the 310 will get pretty hot at 2500 RPM (over 1600F).

 

[gismo]

I have a Lycomming 360 M1-A and cannot find what the EGT settings would be relative to the CHT settings.

So my question is: When leaning an engine out my CHT is about 400 and my EGT is about 1500. Where can I find the correlations & Mid/Max's for a variety of settings

Thanks

I sense a serious lack of engine management knowledge here (not knocking you personally, a significant portion of otherwise good pilots have that shortcoming). I strongly recommend you read John Deakin's old Pelican Post articles on the subject for a decent introduction. For a graduate course try the APS either online or in person. You will learn a lot.

John Deakin: www.avweb.com/news/pelican/182544-1.html

APS: www.advancedpilot.com