"xerj" wrote in message
...
RPM with a constant speed should stay the same (or at least quickly revert
back to the same) shouldn't it?

Yes, the governor will ensure that the RPM remains constant (hence "constant
speed" ).

If so, then it's the MP that would vary as you pull the mixture back. Off
hand, do you remember by how much it varies in a typical type you fly when
you go from best power to best econ?

No, not specifically. To be sure, it doesn't vary by much. But a few
percent change in power (what I might expect with changes in mixture changes
alone, at the most) wouldn't require much of a change in MP. It might not
even be detectable with the typical 2 or 3 inch MP gauge found in most small
airplanes.

Once the mixture is "in the ballpark" on my airplane, whatever change occurs
in MP isn't enough to prompt me to readjust the throttle, I can tell you
that much.

Keep in mind the rest of my post as well. The reference you posted doesn't
provide the details, but it's entirely possible that the "best power"
setting and "best economy" settings DO provide essentially the same power
(within a percent or so), but that the "best economy" setting incurs some
additional engine wear and tear, due to higher operating temperaturs (note
that the "best economy" setting is "Peak EGT").

Pete