Power Management on the O-300

[vmoura]

How do you normally run your engine on climb, cruise, and descent. Do you use full power while climbing all the way to cruise altitude? What altitude do you normally fly on a normal long cross country flight, assuming you can choose from sea level and up? How do you cruise, full power, or do you keep at minimum RPM? While descending do you maintain cruise power keeping an eye on the airspeed?

I saw this post related to power management on another BB and would like to receive your comments on it:

In "Ge there Fast" Mode, I'll use a density altitude above 7000 ft,
run wide open throttle and lean for max rpm.

In "no hurry mode", I'll close the thottle about 1/4 inch to shutoff
the full throttle enrichment, put on full carb heat(in winter), then
lean to max rpm, the continue to lean about 100 rpm off max (or as
lean as the engine will allow). Adding carb heat will sometimes
allow a leaner mixture. Now remember adding carb heat enrichens the
mixture, so the two have to be operated together. I'll compare the
power setting to the table to make sure the plane us below 65% power,
since below 65%, a lean setting will not damage your engine (as long
as it is operating smooth (hitting on all six).

I installed a new tach, that gives me a steady reading. At altitude,
I can see about 100 rpm increase from full rich to a mixture setting
for max rpm. On the lean side, I can take 100 rpm off the tach and
still run fairly smooth.

CHT is more a function of good baffling. If CHT check that your
baffle and baffle seals.

I have a single cylinder CHT and EGT. I reference them, but they
only tell what one cylinder is doing, not all six. These old
carbuerated continental are not know for even fuel/air distribution.
I listen/feel for a smooth engine,
- Peak RPM should give about 75 Deg rich of peak EGT
- Lean to 50 to 100 RPM below peak rpm will peak the EGT.

There is a really good article on AvWeb about engine power management.

[rudymantel]

Never heard of using carb heat for efficient cruise. Carb heat will always decrease power, not only because it richens the mixture (which can and should be compensated for with leaning) but because it re-routes the intake air, eliminating the ram effect.
Rudy

[GAHorn]

Adding carb heat will not allow a "leaner" mixture. Since carb heat provides "hot" air...that air is less dense so the previous mixture is now too rich...so leaning to max efficiency requires a leaner POSITION of the mixture knob...but does not provide a real fuel savings. In fact, the opposite is true. It makes for a less efficient operation.
The only time carb heat should be used for cruise is in severe carb icing condiitons....an extremely rare occurance.
I use full power for takeoff and climb. I use 2450 (just like the book says) for cruise. I lean just like it says also by leaning to max rpm, continuing to lean until first hint of rpm loss, then enrichening to max rpm point again.
I use cruise rpm settings for cruise descents. I reduce power when necessary for steeper descents or pattern work. I also leave the thing leaned until I have to add throttle for any reason. (Such as levelling off and re-setting cruise power or if going around. Remember, since starting descent the throttle had to be reduced to maintain 2450, then less power than cruise has been going on....so no harm in the leaned condition. Any increase in power requires re-leaning/re-enrichening as the condition requires.) I prefer to cruise at 6500-8500 ASL because it places the airplane at max throttle near 2450 and results in the best book speeds/fuel/TAS.
I can't imagine why the person who posted that msg at the other BB would think running it full throttle (and therefore on the power enrichment setting) is somehow a bad thing...but using full carb heat is good. If he thinks full throttle is too rich then he should simply lean it out (which would compensate for the enrichment setting and also allow full manifold pressure and therefore more power.) His operating techniques are contradictory.

[rudymantel]

I lean the mixture same as George but increase rpm with altitude, starting with 2450 at sea level.
The "Cruise performance with lean mixture" table (for a McCauley 7653 prop, 2200 lbs gross and standard conditions) shows 2400 rpm for 69% power at sea level, 2500 rpm for 69% at 2,500 ft., 2600 rpm for 70% at 5,000 ft. and 2600 rpm (the maximum) for 66% at 7,500 ft.
Rudy

[Jeff Matthews]

The carb heat is likely used to improve mixture distribution, allowing more leaning before the leanest cylinder starts misfiring. It would require more manifold pressure for the same power, assuming more manifold pressure is available at the chosen altitude. In theory the fuel burn is less, but that may be picking the bleep out of the pepper.