ENGINE MANAGEMENT
EGT - How to use the instrument
The EGT guage is installed to enable the aircraft to achieve the best economy in the cruise.
Lycoming manual states :
"Best
economy cruise (approx 75% power and below) - Operate at Peak EGT
or if desired drop 50deg F on the rich side of peak EGT""
The basic procedure is as follows:
1. Establish cruise settings. e.g. 2,200 RPM & 22 inchs manifold.
2. Slowly lean the mixture and monitor the increase in EGT
3. Temp will reach a peak - then as you continue to lean it will start to decrease. (Beware of misfire due to too lean)
4. Note the peak temperature on the EGT guage
5. Richen the mixture slightly to achieve a setting of 50deg F below peak.
Note - always increase to fully rich before increasing power settings.
The graph below shows the best economy range.
The green box shows the EGT just rich of peak temperature
The yellow box shows that this setting provides just under max power.
The blue box shows fuel consumption just slightly above best economy.
While
it may look prudent to run the engine at peak EGT to get the best
economy - we only have the guage taking a reading from one cylinder. It
is most likely that one of the other cylinders is running leaner. This
would result in valve damage over time. It is therefore safer to
enrich slightly as allowed by Lycoming. (50deg F below peak)
