Running a Piston Engine 'Lean of Peak EGT'

[NoPax]

Any thoughts on the issue from the professional mechanics out there.

Is this a practice that is bad for the engine, not bad for the engine, worth pursuing or not?

Anybody out there that has done this over a prolonged period of time?

Any research on the issue?

I heard a Malibu pilot one time say he did this to keep the temps in an acceptable range...I kinda thought maybe if he lowered the nose etc etc, he could have avoided having to do that.

 

[USMCmech]

The main problem with running LOP is that the engine will vibrate badly because each cylinder is hitting peak EGt at a different mixture setting. This is notheing other than piss poor quality controll by the engine manufacturers.

If you have GAMIjectors all cylinders will peak at the same time, allowing you to run LOP without shakeing the fillings out of your teeth. Any airplane I ever own will have these installed right away.

THe other problem is that to do this properly without damageing your engine you NEED to have a multicylinder engine monitor. Since HP drops off dramaticly after peak you need to be running your EGT just outside the dangerzone peak EGT if you don't want to fly too slow.

Is this a practice that is bad for the engine, not bad for the engine, worth pursuing or not?

Once you have the vibration problem and the insrumentation problem solved, it is completely harmless and may infact be better for your engine. Since there isn't any unburned fuel when LOP you don't have to worry about lead fouling.

You can deffinately save a lot on fuel.

Anybody out there that has done this over a prolonged period of time?

Yeah, all the old piston engine airliners and Bombers from WW2 ran this way all the time. They used diferent instrumentation to achive the same result.

Any research on the issue?

http://www.avweb.com/news/columns/182146-1.html

 

[NoPax]

Thank you so much

Great post. At first the practice seemed unusual to me, but it's starting to make more sense.

 

[cforst513]

i was always told to fly 50 rich of peak.

 

[PAPA FOX!]

i was always told to fly 50 rich of peak.

Unless below 60-65% power that actually is the WORST place to run an engine. The CHT's and peak pressure are the highest when run there. If you are operating at 50 ROP and rich OR lean it the CHT's will be cooler! I wish more pilots knew this. I only learned it on the link that USMC posted. Very useful to know!

 

[NoPax]

i was always told to fly 50 rich of peak.

Actually I was taught to fly 50º lower than peak - so work that one out! Yes you can go either way - rich or lean to get the same result.

In the airplane I'm currently flying - an Aero Commander 500B - the exhaust stacks (on top of the engine) leave a nice residue on the top cowlings.

If the residue is white - it has been run lean
If the residue is grey - it has been run at peak
If the residue is brown - it has been run too rich

At least that was what I was told, and it seems to make sense.

I've been flying them for about 1100hrs, and have only had one problem with the engine, probably unrelated to how I was running it (a push-rod valve seal gave in), and I do run them as lean as possible, but I'm without the GAMI injectors and sensors for each cylinder/exhaust stack. There is talk about getting them, but it would be expensive. My residue is always pure white.

When I swap out an airplane with the other pilot, usually his is greyish.

And what are you doing over here anyway...

 

[Lead Sled]

Unless below 60-65% power that actually is the WORST place to run an engine. The CHT's and peak pressure are the highest when run there. If you are operating at 50 ROP and rich OR lean it the CHT's will be cooler! I wish more pilots knew this. I only learned it on the link that USMC posted. Very useful to know!

John Deakins has some pretty good articles at www.avweb.com and you can also get more information on LOP operations at www.gami.com

'Sled

 

[banned username 1]

I spoke with Bruce Bohannon, pilot of the Exxon Tiger who does all of the time to climb and altitude records in his highly modified RV/Rocket/who-knows-what and he said you can do almost anything as far as leaning goes as long as it's below 75% power.

That was great advice about the vibration issue and makes a lot of sense. I know when I'm flying my RV-8 and watching the fuel flow, the thought of 100LL selling for over $4 a gallon takes a little joy out of the rest of the fun.

 

[avbug]

Unless below 60-65% power that actually is the WORST place to run an engine.

Ah, no. Stochiometric, often referred to as peak, is where the most complete combustion takes place, and also where temperatures are highest.

Pilots who run slightly rich of peak are risking running some cylinders at peak, because the cylinders don't run the same (due to a number of factors). At operations greater than 75% rated power, one stands a chance in some engines of detonation when operating close to peak, especially in the presence of superheated carbon or lead deposits in the cylinder.

Running Lean of Peak has been standard practice in some engines for a great many years, and yes, temperatures are cooler than at peak. Rich of peak, you can think of lower temperatures as being fuel cooled, and lean of peak you can think of lower temperatures being air cooled.

GAMI is nice, but not the be-all nor end-all of products.

Many pilots using EGT as a reference to establishing mixture settings think the markings on the alcor guages mean something, and they don't. The company removed the temperature markings a long time ago when they figured out all the gauges couldn't be calibrated the same, or consistantly, and went with hash marks to represent nothing more than general reference points. Each tick isn't really 25 degrees.

Pilots also fail to realize when trying to fine tune their engine to a gnat's breath of refinement, that gauges and instruments put in the cockpit are cheap idiot gauges which seldom give accurate information. That goes for temp, voltage, etc. That's why when working on the equipment, we use calibrated test equipment instead of cockpit instrumentation.

The various multipoint cht and egt systems are dandy, except that very seldom, if you take the time to pull and test each thermocouple for calibration, will you find them calibrated properly or delivering accurate information. The instrument only gets an electrical signal from the thermocouple probe, it needs to know how that signal equates to temperature. Grab five different probles and immerse them in the same hot liquid, and you'll get five different readings.

I've never seen an engine shake itself off the mounts or crack a mount if it's run lean of peak and everything is properly calibrated, and one doesn't need gami injectors to do that. If you're getting vibration as described before, then you've got far more wrong with your engine than slightly differing injector deliveries, and you're probably experiencing detonation. That's another matter completely.

In the airplane I'm currently flying - an Aero Commander 500B - the exhaust stacks (on top of the engine) leave a nice residue on the top cowlings.

If the residue is white - it has been run lean
If the residue is grey - it has been run at peak
If the residue is brown - it has been run too rich

At least that was what I was told, and it seems to make sense.

Sounds good, in theory. Those deposits...those white depoits...that's lead. Tetraethyl lead, burned and processed in your engine, and it's very toxic. Grey doesn't mean it's been run at peak, white doesn't mean it's been run lean, and brown could be several factors, but likely includes the burning of oil.

I've set mixture by the color of flame in the exhaust collector stacks, but setting it based on the color of your exhaust stains is asking for trouble.

 

[UA-RESURRECTED]

Stochiometric, often referred to as peak, is where the most complete combustion takes place, and also where temperatures are highest.

Would that be strictly exhaust temperatures, or general engine temp??? I always thought that running an engine too lean resulted in higher engine temperatures. Were you only referring to exhaust temps?

At operations greater than 75% rated power, one stands a chance in some engines of detonation when operating close to peak...

So would you agree with the practice of using a "full-rich" setting whenever operating above 75% maximum power? This is the basic premise of what I was taught, unless the density altitude is higher than 5,000'.

lean of peak you can think of lower temperatures being air cooled.

Here again, I always though that too lean meant too hot. You seem to state the opposite, that temperatures are cooler with leaner mixtures. This doesn't seem likely. Can you clarify?

Also, what about engines with a tachometer only? Leaning for best power is easy, but does anyone have a procedure for leaning for best economy with a tachometer only?