"Jim Macklin" wrote in message
news:7ilwf.41026$QW2.13106@dukeread08...
I'll buy that, always best to use specific data rather than
a generic answer. It takes a pretty good eye and tach to
see 5 rpm.



Sure does. And a digital tach may flicker that much. Sometimes it is
called a "barely perceptible rise".

Some say it is easier to observe a rise in MP than such a small RPM rise,
and that is borne out by my observation.
The MP will rise one to two inches, and the MP gauge seems to be more stable
than the tach.

If the mixture is set to spec, it is not necessary to lean for ground ops,
since it is already lean enough to prevent plug fouling. Ground leaning is
effective only if leaned back to the edge of idle cutoff, anyway.

The Lycoming manual doesn't seem to have any tables for adjusting RPM rise
for density altitude. If it is leaned to the 5RPM rise spec at a high
altitude airport, I wonder if it might be too lean at a low-altitude
airport, with no way to enrichen it.

Stan