Peak EGT for best service life?

[Apollo]

For the ultimate screwed up discussion of this topic, you can't beat this for rubbish:

http://www.aopa.org/News-and-Video/All- ... an-of-peak

This guy just blows hot air throughout his article. Incredibly, in the second paragraph, he says this:

Fly a carbureted airplane? Don’t have an EGT gauge or an engine analyzer? Want to fly at 50 degrees rich of peak? Then simply lean the mixture until the engine begins to run rough, then enrichen the mixture slightly—until the roughness goes away. It’s as simple as that.

Anyone paying attention will realize that rough running via this method is because the engine is too lean, and enriching it "until the roughness goes away" will result in a LEAN OF PEAK mixture as you are once again supplying enough fuel to get good combustion, but not yet enough to increase EGT.

I rest my case.

So... MONITOR YOUR TEMPERATURES, and operate the engine smoothly (not just in terms of leaning, but in terms of operation generally). The biggest killer of an engine is running things too hot.

For a discussion of detonation and pre-ignition, this is worth a read: http://www.contactmagazine.com/Issue54/ ... asics.html

[Great Ozzie]

I don't think pre-ignition is possible in the Comanche 250 at cruise power regardless of mixture and temps.

Scott.

I wouldn't think so either, Scott... even detonation. I'd imagine true for any engine - of course, as long as abiding by the manufacturers recommendations including octane etc.

I have a question, I have already asked this regarding the IO-540 in the Cessna 182, but the Comanche uses a carburetted O-540.
Simply, for minimal wear on parts and best service life, is it recommended to run on peak EGT? Or something different, like 125°ROP? After doing a little research I am currently cruising at peak.

Just to reiterate, Lycoming - in their leaning procedures for "max service life for continuous cruise operation" - recommend staying below:

• 65% Power
• 400°F CHT Max.
• Oil Temp between 165°F and 220°F.

Some heat is good. Too much or too little is not. You know worst places typically are on the ground and takeoff because of the reduced cooling air flow. And of course, in the climb (until higher) you are operating well above 75% power. For specifics, checkout Lycoming Service Instructions and download "SI 1094D - Fuel Mixture Leaning Procedures" near the bottom of the page.

We don't have a Continental in any of the recent GA stuff, but fwiw it can be found at: Continental Service Bulletin Search. Just find "M89-18 Exhaust Gas Temperature (E.G.T.) Recommendations for Standard Engines (Leaning Lean)"

Fly a carbureted airplane? Don’t have an EGT gauge or an engine analyzer? Want to fly at 50 degrees rich of peak? Then simply lean the mixture until the engine begins to run rough, then enrichen the mixture slightly—until the roughness goes away. It’s as simple as that.

Idk about the "50 degrees rich of peak" part... but the rest sounds just about like the Lycoming's recommendation for Best Economy.

[Apollo]

Interesting... Continental only refer to EGT for fuel economy, unless fitted with an "engine analyzer, but even then they only reference peak EGT for the purposes of not exceeding max operating temperature limits.

For economy of fuel and extended range, do not lean the mixture below 50 degress F. rich of peak

So they are saying that leaning further increases fuel consumption? How?

[Oracle427]

Efficiency and performance drops resulting in more fuel consumption for less power.

[Scott - A2A]

The reason why we worked so hard on the "lean by ear" feel is, especially in a carbureted engine, not matter what the EGT indicates, the ear is the best final device IMO, even over a full blown engine analyzer.

In other words, if the EGT tells you things are OK, yet there are some skips, you tune to remove the skips by ear. At the same time, if you can squeeze a bit more and maintain smooth performance than the EGT indicates, your ear knows best. At least, this is the way I fly - not speaking for all.

Scott.

[av8erjm]

In the time I had with the Comanche never ran lean of peak always 5 or so degrees rich and while other guys were leaning past peak they were replacing jugs ours lasted to TBO. The A/P's will admittedly say they love for guys to run lean of peak, it's money in their pocket

edit: we also had a EI engine analyzer for ultimate performance

[Scott - A2A]

It's hard to run lean of peak with a carbureted engine.

Scott.

[n72.75]

I don't think pre-ignition is possible in the Comanche 250 at cruise power regardless of mixture and temps.

Scott.

180°F OAT with the filter soaked in diethyl ether.

[av8erjm]

my brain fart, N7727P was STC'd for fuel injection, I'll be going to my room now

[AKar]

It's hard to run lean of peak with a carbureted engine.

Scott.

Yes, if one leans until the engine gets rough, likely one or more cylinders are running lean of peak while others can be quite a bit rich of peak, or anything in between. It is good to note that in such kind of operation, the cylinder that is the leanest, where the EGT gauge is supposed to be, is not the 'hottest' or most stressed one as measured with CHT gauge. Of course, in airplane installations the uneven cooling of the cylinders may, and likely does, mask which one is actually running hottest due to combustion alone. All this applies to many fuel injected engines too, which have not been tuned carefully for even mixture distribution.

-Esa