If you set cruise RPM to 2400 and lean the engine, RPM will
increase as combustion is improved and power increases
(fixed pitch prop). Peak power is max RPM, some books
recommend running richer, enough to drop the RPM 50. Ground
idle mixture is set so that RPM increases 20-50 RPM as the
engine goes from rich idle to cutoff and the mixture leans
out.


"Thomas Borchert" wrote in
message ...
| Jim,
|
| 50 RPM drop on the rich side is too rich at cruise...
|
| RPM doesn't matter.
|
| 50
| degrees rich of peak on the EGT is about right with a
carb.
|
| Why? How? 50 ROP is the point of maximum internal
combustion pressure.
| A point at which you don't really want to be.
|
| With fuel injection, just a little below peak or even at
| peak if the cruise power is set below 70%.
|
| below peak on the rich or the lean side? A limit of 70 is
artificial.
| 65 and 75 is mentioned by the engine manufacturers,
respectively. Many
| say those limits don't mean that much. CHTs do. Many
people run their
| engines lean of peak (well lean of peak) at 80 percent and
more. CHTs
| stay well below 380.
| There is no difference in leaning technique between carb'd
and injected
| engines.
|
| At low power
| settings you can run at peak since the actual
temperatures
| will be low.
|
| What temperatures? EGT? CHT? Actual EGTs don't matter
anyway. Actual
| CHTs are higher ROP than they are at peak EGT. They
shouldn't be above
| 380.
|
| If you have a calibrated EGT (TIT) follow the
| limits.
|
| Absolute EGTs don't matter. TIT is a different story,
since the engine
| is turbo'd.
|
| I really recommend reading Deakin's columns at Avweb - it
makes you see
| several lights real quick.
|
| --
| Thomas Borchert (EDDH)
|