fuel and maintenance saving will pay for the seminar
I don’t think so… reality is much simpler.
Thank you all for the quick responses. @Peter I read your article as well, and it clears things up a lot.
For higher altitude, lower power cruise settings I can’t go exactly peak EGT like you do, as that’s explicitly forbidden for this installation (see POH snippet). But the POH suggests a “Maximum range” cruse setting that is 25F ROP (to be used below 65% power), which I guess is similar. That’s probably very close to what I was describing in my opening post, which is "a little bit leaner than normal 75F ROP cruise.
For low altitude, I guess I can either set a low power setting and do the above, or go 75%, but then stick with the richer mixture recommended by the POH, right?
25F ROP is identical to peak EGT. The curve around there is so flat it makes no difference. So yes this will be “best range”.
Also LOP operation, while not authorised, cannot do harm because everything is cooler. But there is no point in exploring that if you get uneven running. You don’t get more MPG with LOP.
For higher altitude you are limited by air pressure. The operating ceiling is always reached at “best power”. Always wide open throttle, max RPM, and lean for best power which is generally found at the sea level takeoff EGT (1300F for mine).
For low level, say a few k feet, most experts seem to agree that 65% power is the best compromise for engine life, economy, etc. I just set 23" 2400rpm and set the fuel flow for peak EGT which for mine is 11.7 USG/hr. The RPM also doesn’t matter much; 2300-2400 is all fine. I would not fly at 75%.
I used to fly behind an O-470-U all the time, with a single-point Cessna EGT. I flew it at 18"/2100 rpm at peak EGT and it used to burn 36 litres per hour. It was economy motoring for sure, as the C180 was indicating 116kts which was faster than a C172 with the same fuel burn.
On other airframes, I would happily fly by reference to CHT only, guided by the book figures for fuel flow for that cruise profile if there was an engine monitor fitted.
Peter wrote:
For low level, say a few k feet, most experts seem to agree that 65% power is the best compromise for engine life, economy, etc. I just set 23" 2400rpm and set the fuel flow for peak EGT which for mine is 11.7 USG/hr. The RPM also doesn’t matter much; 2300-2400 is all fine. I would not fly at 75%.
Interestingly the 23/2450 you quote is just about 75% per my table, which is the book-recommended “cruise-climb” I usually use. For cruise it’s 23/2300 at most which is 70-75%, but you’re right that 22" should probably help the engine while not losing much speed. And usually those low level flights are for enjoying scenery anyway, not for going places.:)
I was wondering how is it possible that the same MP / RPM combination is listed as 65% for you but 75% for me. While yours is larger, according to my understanding that shouldn’t matter: both are NA, even the RPM limit is similar (yours is 2575, right? mine 2600), both are leaned approximately the same way. Maybe there’s something up with Cessna’s air intake that prevents getting close to the 30" MP at WOT sea level? To be honest I can’t recall the exact values I’m used to seeing during the takeoff roll.
Interestingly the 23/2450 you quote is just about 75% per my table
That depends on the fuel flow (the mixture).
I was wondering how is it possible that the same MP / RPM combination is listed as 65% for you but 75% for me
Probably the fuel flow 
At peak EGT, two engines of different size, at the same fuel flow, will deliver a similar HP.
Maybe there’s something up with Cessna’s air intake that prevents getting close to the 30" MP
Possible but very unlikely. A few years ago I tried a different air filter, claimed to improve power. K&N or some such. It made no difference to MP…
