I've never owned an airplane with a decent EGT gauge, so have always leaned by ear. You know, dial it back until it runs rough, then wind it back in a turn or two. My current airplane has a sporadically working single-point EGT which I was just gonna remove, but now I think I'm gonna replace it and the probe.
So now I'm thinking about everything I've heard or read about leaning by EGT. Seems like most people like "50 degrees lean of peak". What's the reasoning here? I'm no rocket scientist, but it seems to me that peak EGT would indicate the most efficient combustion and therefore maximum efficiency. Also, who can tell me where "lean until rough, then richen up a bit" falls on the compared-to-peak scale?
FWIW a local guy, who used to own a business that specialized in "re-chipping" cars for better performance, says that it should be all about percent of oxygen in the exhaust, and that XX % is optimum. He's trying to get an STC for a sensor and gauge set-up for monitoring this.

You can learn a great deal about LOP operations from several good sources.

EAA videos - search for the Mike Busch seminars

Pelicans Perch through avweb. Search for the John Deakin articles on LOP.

Take a course through Advanced Pilot Seminars.

Your questions will be answered.


Here are some things to consider FWIW:

You are likely running a carbureted engine? Might be a bit tougher to get the mixture distribution balanced enough to run LOP. Some guys do it with partial carb heat, but I don't know how balanced they really get.

The procedure for leaning to roughness and richening is a technique for leaning when you don't know what your temps are doing, but I think it is usually for best economy at reduced power settings. Don't do this at 75% power where your peak pressures might be too high.

The amount of leanness beyond peak depends on your power setting to keep you away from the Red Box and potential for detonation. The higher the power, the more LOP you must be. Below a certain point, running at peak will not cause harm (similar to the best economy technique of leaning to roughness and then richening to smoothness). 50 deg LOP is fairly safe at most cruise power settings which is why many people like this, but again, it depends on how much power you are making.

LOP operations are made much easier with an injected engine with balanced injectors and a multi probe engine analyzer.

When ROP, excess fuel can cool the engine. When LOP, engine depends on air to cool. Baffle integrity is important.

Power when ROP is determined by RPM and MP combinations. Power when LOP is determined by fuel flow.

The answers to your seemingly simple questions are actually a bit complicated, but if you research the topic using the resources listed above, it will make sense.

Good luck!

This topic is going to open up a hornets nest, but my personal opinion is that you should read everything you can from Mike Busch and John Deakin. They've completely changed how I manage piston powered aircraft engines, and have saved me a ton of money in the process.

50 LOP might be tough unless your engine is superbly balanced from cylinder to cylinder, but I run 20 LOP in my O-470S and it's absolutely smooth.

Try these to start:
https://www.jpinstruments.com/wp-conten ... ed-Fin.pdf

http://www.gami.com/articles/egt_myths.pdf

Once you've read them, read them again. Then go flying, play with various techniques, land and read them again.

He's a great writer, but it took a few run throughs before the information became intuitive for me. It's completely counter-intuitive to everything I was taught way back when.

hotrod180 wrote: Seems like most people like "50 degrees lean of peak". What's the reasoning here? I'm no rocket scientist, but it seems to me that peak EGT would indicate the most efficient combustion and therefore maximum efficiency.

It keeps you from burning valves at above about 65% power.

I like to go 100 degrees for climb out. Keeps everything a little cooler!

hotrod180 wrote: FWIW a local guy, who used to own a business that specialized in "re-chipping" cars for better performance, says that it should be all about percent of oxygen in the exhaust, and that XX % is optimum. He's trying to get an STC for a sensor and gauge set-up for monitoring this.

Oh, there is no doubt that you could use a gauge to maximize absolute engine performance but I fear you will melt your cylinders. The multi probe engine analyzers keep you from doing harm to your $30,000 engine at the cost of reduced efficiency. For me, engine protection is more important than maximum performance. But I don't race in Reno either.

TangoFox wrote:

hotrod180 wrote: Seems like most people like "50 degrees lean of peak". What's the reasoning here? I'm no rocket scientist, but it seems to me that peak EGT would indicate the most efficient combustion and therefore maximum efficiency.

It keeps you from burning valves at above about 65% power.

I like to go 100 degrees for climb out. Keeps everything a little cooler!

And above 85% you need more like 100F LOP - or close to full rich, so it's a sliding scale.

You need to know what you're doing, if you want to run as close to peak as possible.



Remember, "peak" EGT changes with RPM, altitude, and a whole bunch of other things.

Above ~7k ft, I find I can run at peak safety because the engine wont make more than about 65% power, depending on the day. On colder days, maybe 8k or more.

In my first airplane (a stock 1970 182 with the ubiquitous O-470), it was lean by ear--no EGT gauge at all, only a single point analog CHT. The airplane had about 300 hours on it when we bought it in 1975, we ran it a lot, and in 1977 it needed a valve job in 2 of the cylinders. We had a quickie job done, but the next year, with about 1300 hours on the clock, we had enough bad valves that we opted for a complete overhaul. The overhauler recommended that we consider installing a multi-point EGT gauge, but all that was available at that time was a manually switchable version from Alcor. We didn't do it, and the next year we traded the airplane off for the new TR182.

The TR182 had a turbocharged carbureted Lycoming 540 engine and a single point analog EGT/CHT. Apparently they picked the right cylinder to put the probes on, because over the next couple of years, the only engine problems we encountered were some spark plug fouling, pilot induced by one of the pilots we rented it to. That airplane had gobs of problems, but most were peripherals and not the engine. We ran it about 50 ROP, based on the recommendations of both our local mechanic and the chief mechanic at the dealer.

We traded it off on the last model T210 which came from Cessna before the SE lines were shut down. It also had only a single point analog EGT. I got out of the partnership 8 months later, before any engine problems surfaced, but we also ran it 50 ROP.

When I purchased my P172D 10 1/2 years ago, it was equipped only with a single point analog CHT and no EGT. My IA had a used digital EGT/CHT from a wreck, which he installed after my new engine was built. I ran 50 ROP using that until I had an Insight G1 installed several years ago, one of the first sold in the US (it's a Canadian product). It provides 4 point EGT/CHT digital, but it also has changing-color bar graphs that can be read at a glance.

It taught me that my back 2 cylinders had been running way too hot, so I've experimented with different degrees of ROP to try to cool them, tried to run LOP with and without carburetor heat, etc. Different timing seemed to make a big difference in the overheat problem (recommended in a personal email from Mike Busch). Trying to run LOP has proved unworkable--the engine gets rough just to the lean side of peak, and it can't be smoothed out with carb heat, partial or full.

It also taught me that there is a huge variation of the EGTs from one cylinder to another. So what I do now is lean to peak on the first cylinder to peak, then enrichen it about 25 degrees. Then I pull the carb heat on, which does a great job of evening out the variation. Then I push the carb heat back in, and it stays pretty even, with one cylinder at 25 ROP and the others a little richer.

Does all of this help the engine's longevity? Heck, I don't know! The engine has good compressions at about 700 hours, but that doesn't tell me much. Does it help with "mileage"? Nope--it's still at about 9.8 gph at 8-9000' MSL, somewhat less at higher altitudes, just like it was before the Insight was installed.

With all that information, I'll bet you're thinking, "why bother?" For me, I like knowing what's going on with my engine, but whether it's helping it, I can't really say.

Cary

Battson wrote:...........
And above 85% you need more like 100F LOP - close to full rich, so it's a sliding scale. .......

Question, how do you know "close to full rich" above 85% power is 100 lean of peak? You can't really richen it up any more to see just where that peak is, eh? I'd think it wouldn't work to go by what the peak temperature is at lower power settings.
Cessna designated what cylinder to put the CHT probe on, TCDS says on #2 through s/n 18051445, on #1 s/n 18051446 (1965) through 18052500, and on #3 s/n 18052501 (1975) and up. My K-powered 53 model has it on #2. Cessna doesn't seem to designate where to put the EGT probe-- can't remember for sure, but mine is either on #3 or on the collector from #1, 3, & 5. Seems like maybe the EGT should be on the same cyl as the CHT, but what do I know?

hotrod180 wrote:

Battson wrote:...........
And above 85% you need more like 100F LOP - close to full rich, so it's a sliding scale. .......

Question, how do you know "close to full rich" above 85% power is 100 lean of peak? You can't really richen it up any more to see just where that peak is, eh? I'd think it wouldn't work to go by what the peak temperature is at lower power settings.

Sorry I think we're talking at cross purposes - I added the work "or" to my post to clarify.

So at 85% power you would theoretically need 100 LOP to remain a safe margin from detonation, or on the rich side of things you need basically full rich. Lycoming recommends full rich above 75% anyway.

If I pulled power from full rich, my engine management system records the EGT as it goes through peak, or I can watch the gauge readout, so when I stop leaning the I have seen / the computer tells me where I am relative to peak. And yes you want to lean through the peak as quickly as you can, to avoid letting things heat up.

I don't like to run it exactly on the red line leaning limit, I prefer to stay a safe distance away from the red zone.

hotrod180 wrote:. Seems like most people like "50 degrees lean of peak".

Don't you mean RICH of peak?

Have you consulted the manufacturer's owner's manual and online documentation on leaning. Continental has a technical paper online addressing leaning.

I don't know anything about what I've listened to and read from Busch and Deakin. I thought 50f rich of peak was right where you didn't want to be, the mixture that provides peak pressure? And isn't EGT just a measure of the amount of energy getting blown out the exhaust? All this stuff is very interning to me and I'm just starting down the learning path.

PA12_Pilot wrote:

hotrod180 wrote:. Seems like most people like "50 degrees lean of peak".

Don't you mean RICH of peak?

Have you consulted the manufacturer's owner's manual and online documentation on leaning. Continental has a technical paper online addressing leaning.

Historically that is where people used to run their engines for a number of reasons.
It's since been proven that 50F RICH of peak is about where the engine develops the highest cylinder head pressures, and that means the engine will probably run the hottest (CHTs) at 50 ROP, and running hot has the greatest risk of reducing the engine's service life. Aluminium gets really soft when it's hot. If it gets hot enough and you're working it hard, it can cause detonation or even pre-ignition, but you have to really work it hard for that to happen.
Of course I am grossly simplifying, but that is the general gist of it.

So 50F ROP is a bad place to run in most situations.
But 50F LOP is good under most conditions, except very high power settings e.g. take-off and max performance climb.

You have basically two logical choices:

1. Purchase and install a good six cylinder graphic engine analyzer, and TRY running lean of peak, AFTER learning everything you can about LOP ops.

Or:

2. Keep what you've got, and continue leaning by ear.

Bear in mind that the O 470 is one of the more difficult carbureted engines to get to run well LOP. It can be done, but it takes a bit of fiddling, and some of those engines just don't seem to like LOP.

Finally, if you're going to run LOP, you really need to learn the procedures, and follow them to the letter every time you lean LOP.

Notwithstanding the assertions of the "LOP Cult" you can damage an engine running LOP if you don't lean properly.

I'd get a graphic engine monitor in any case.

MTV