Hopefully soon to be new owner, looking for tips on flying most efficiently

[RescueMunchkin]

I see the term running LOP (Lean of Peak?) used a lot, but is there a writeup on how to find this mixture setting and fly safely with it applicable to M20F?

And how does running LOP work if the plane is also potentially manually wastegated turbo normalized?  Is most of the turbo's benefit the ability to fly higher to get stronger tailwinds, or are there other fuel efficiency benefits by flying at higher altitudes?

Thanks in advance!

Edited October 24, 2023 by RescueMunchkin

[KSMooniac]

Welcome.  There is a TON of discussion over many, many years so try searching on the topic.  That will lead you down a deep rabbit hole.

If you want the BEST and most effective method of learning on the broad topic of piston engine operation, consider taking the online course found at www.advancedpilot.com.  There is a lot of legacy bad information, including stuff published in vintage POH's from many airframe manufacturers, that is not correct, nor best practice for engine efficiency or longevity.  I strongly encourage every pilot and especially every owner to make the effort to get educated, and to get a decent engine monitor after they learn how to use it.  I'm not affiliated with APS in any way, just a happy customer from 16 years ago.  I learned more there at the live seminar in 2.5 days than I did in some semester-long engineering courses.

A turbo-normalized piston engine can be the most efficient in the GA sphere if operated LOP.

[Pinecone]

If you look on AVWEBB for Pelican's Perch articles by John Deakin, there are a number on LOP operation.

The best thing to do is the APS seminar https://www.advancedpilot.com/

They are only doing the online course, but that is good.  In person is even better if they start those back up.

You MUST have an engine monitor with individual probes and readouts of the EGT and CHT for all cylinders.

The short thing is, if you lean from full rich, the EGTs will go up as you get leaner, until they hit a peak and start going down.  LOP operation means you are running the engine in the range where all cylinders have peaked and are on the lean side where leaner is cooler.   There is a range from peak to about 100 degrees rich of peak where you risk damage to your engine at higher power settings. 

When LOP you are burning every molecule of fuel (or close to it) so you get the best fuel economy.  And cooler temperatures.  Good things for your engine.

Normally aspirated, turbo normalized, and turbo all work in a similar manner.

[Bolter]

If you are technically inclined, this graphic from Lycoming (red annotations are mine) may be helpful to understand what happens in the cylinder as a function of rich to lean mixture.Lycoming Power-EGT-CHT relationship.pdf

[RescueMunchkin]

17 hours ago, Pinecone said:

The short thing is, if you lean from full rich, the EGTs will go up as you get leaner, until they hit a peak and start going down.  LOP operation means you are running the engine in the range where all cylinders have peaked and are on the lean side where leaner is cooler.   There is a range from peak to about 100 degrees rich of peak where you risk damage to your engine at higher power settings. 

When LOP you are burning every molecule of fuel (or close to it) so you get the best fuel economy.  And cooler temperatures.  Good things for your engine.

Normally aspirated, turbo normalized, and turbo all work in a similar manner.

Thank you - the thought of running leaner than what gives peak EGT is a scary concept to me, probably because I'm used to the car world where positive boost and running lean is a huge no-no.  The ~4 hours of Mooney M20 with O320 training taught me to lean until the single EGT gauge was about 100 degrees richer than a red line marked on the gauge during climbs and I could get close to that red line during cruise (but the engine would run rough before hitting it).  In Cessnas, I was taught to lean until the engine RPMs started to decrease, then richen a tiny bit.

I understand that with a Rajay turbo on the M20F, it's only supposed to be used to bring the MP back to ~25 inches when I'm at altitude, so theoretically, I could run the same mixture settings if I were at a naturally aspirated 25 inches.

[Pinecone]

The issue is, there is lean and then there is LEAN.  Lean of best power puts you right in the danger zone.  Lean of peak puts you in a safe area.

Also, performance cars are tuned for 100% power.  In aircraft, that is take off and climb and typically done at full rich.

They problem with leaning to a given EGT is that the peak EGT can change based on various factors.  So you might be LOP or might be right in the danger zone.

Do some of the suggested reading.  Also, the first lesson of the APS program is available free on there website.

[Fly Boomer]

1 hour ago, RescueMunchkin said:

Thank you - the thought of running leaner than what gives peak EGT is a scary concept to me, probably because I'm used to the car world where positive boost and running lean is a huge no-no.  The ~4 hours of Mooney M20 with O320 training taught me to lean until the single EGT gauge was about 100 degrees richer than a red line marked on the gauge during climbs and I could get close to that red line during cruise (but the engine would run rough before hitting it).  In Cessnas, I was taught to lean until the engine RPMs started to decrease, then richen a tiny bit.

I understand that with a Rajay turbo on the M20F, it's only supposed to be used to bring the MP back to ~25 inches when I'm at altitude, so theoretically, I could run the same mixture settings if I were at a naturally aspirated 25 inches.

Take @Pinecone advice, and get the APS stuff.

[RescueMunchkin]

Signed up for that site, scored 34% on that "fun" test lol

[Bolter]

11 hours ago, RescueMunchkin said:

Thank you - the thought of running leaner than what gives peak EGT is a scary concept to me, probably because I'm used to the car world where positive boost and running lean is a huge no-no.  The ~4 hours of Mooney M20 with O320 training taught me to lean until the single EGT gauge was about 100 degrees richer than a red line marked on the gauge during climbs and I could get close to that red line during cruise (but the engine would run rough before hitting it).  In Cessnas, I was taught to lean until the engine RPMs started to decrease, then richen a tiny bit.

I understand that with a Rajay turbo on the M20F, it's only supposed to be used to bring the MP back to ~25 inches when I'm at altitude, so theoretically, I could run the same mixture settings if I were at a naturally aspirated 25 inches.

Most modern street cars are running very lean of peak until you demand power.  It helps with fuel econ and emissions. 

Lean of Peak is not a big deal, as long as you are doing it at the right time, as in not LOP during takeoff and high power climbs.  Cruise and descent are great opportunities for very efficient lean operation.  Some wise people have also demonstrated good effects on the engine by running LOP instead of ROP for the same % power.

Which Mooney has an O-320?  Is that the original engine of the M20A or B?  C, E, F G, and J are Lycoming 360's.

It has been said, but I cannot validate this, that the old fashioned leaning until rough, and then rich to smooth will put you LOP.  My J with the IO-360 would not get rough until LOP (verified with 4-point engine monitor).  With the Continental IO-550, it does not get rough until its so lean it might shut off.  

-dan

[EricJ]

8 minutes ago, Bolter said:

Which Mooney has an O-320?  Is that the original engine of the M20A or B?  C, E, F G, and J are Lycoming 360's.

The dash model, i.e. the M20, the one before the M20A, had an O-320.    

[RescueMunchkin]

3 hours ago, Bolter said:

Which Mooney has an O-320?  Is that the original engine of the M20A or B?  C, E, F G, and J are Lycoming 360's.

I'm sorry, I totally messed up..I trained in one with the 180hp carbureted O-360

[Pinecone]

8 hours ago, Bolter said:

Most modern street cars are running very lean of peak until you demand power.  It helps with fuel econ and emissions. 

Lean of Peak is not a big deal, as long as you are doing it at the right time, as in not LOP during takeoff and high power climbs.  Cruise and descent are great opportunities for very efficient lean operation.  Some wise people have also demonstrated good effects on the engine by running LOP instead of ROP for the same % power.

Which Mooney has an O-320?  Is that the original engine of the M20A or B?  C, E, F G, and J are Lycoming 360's.

It has been said, but I cannot validate this, that the old fashioned leaning until rough, and then rich to smooth will put you LOP.  My J with the IO-360 would not get rough until LOP (verified with 4-point engine monitor).  With the Continental IO-550, it does not get rough until its so lean it might shut off.  

-dan

Yes, computer control allows modern car engines to vary the mixture as needed, along with ignition timing and in some, valve timing.  There is a balance, as LOP makes more NOx, which is a parameter for pollution control.

In cars, it is funny, we spend decades to get people to understand that increasing the octane of the fuel did not, by itself, increase performance.  But now, with modern engines, many will put out more power with higher octane fuel.  My 2002 M3 needs about 96 AKI to make max power.

Before GAMI forced Continental to do something about it, IO-550s would NOT run LOP as delivered.  They had the 3 rows of cylinders running at vastly different mixtures.  I think the GAMI site still outlines this.

[larryb]

Efficiency is not just the red knob, it's also the black knob. I use 60% power LOP as my cruise power setting. I also hope to have reduced engine wear at this power setting.

Altitude has more advantages than simply tail winds:

• TAS increases as you climb since the air is thinner. Around 2% per thousand feet. So 120kt IAS at sea level is 145 Kt TAS at 10,000. Since you are going faster on the same fuel mpg is increased. 
• Ride is smoother. A bumpy ride at 3000 feet is a smooth ride at 10,000 feet.
• Increase glide range in case of a problem.

For me, shorter flight between 1 and 2 hours are 10K to 12K. Longer than 2 hours is typically 15K to 17K. If the headwinds at altitude are too great I may elect to suffer in the bumpy air lower.

[RescueMunchkin]

On 10/27/2023 at 7:52 AM, larryb said:

For me, shorter flight between 1 and 2 hours are 10K to 12K. Longer than 2 hours is typically 15K to 17K. If the headwinds at altitude are too great I may elect to suffer in the bumpy air lower.

Thanks, that helps...I obviously haven't done any flying at oxygen recommended altitudes yet, so I'll investigate this more. Planning to do several XC trips that will be 3-4 hours, but they may require bathroom break intermediate stops.

[Pinecone]

5 hours ago, RescueMunchkin said:

Thanks, that helps...I obviously haven't done any flying at oxygen recommended altitudes yet, so I'll investigate this more. Planning to do several XC trips that will be 3-4 hours, but they may require bathroom break intermediate stops.

Travel John piddle packs from Amazon.

Once you get up in the teens, you don't want to make any stops.

[ArrowBerry]

 

On 10/24/2023 at 5:32 PM, Pinecone said:

If you look on AVWEBB for Pelican's Perch articles by John Deakin, there are a number on LOP operation.

The best thing to do is the APS seminar https://www.advancedpilot.com/

They are only doing the online course, but that is good.  In person is even better if they start those back up.

You MUST have an engine monitor with individual probes and readouts of the EGT and CHT for all cylinders.

The short thing is, if you lean from full rich, the EGTs will go up as you get leaner, until they hit a peak and start going down.  LOP operation means you are running the engine in the range where all cylinders have peaked and are on the lean side where leaner is cooler.   There is a range from peak to about 100 degrees rich of peak where you risk damage to your engine at higher power settings. 

When LOP you are burning every molecule of fuel (or close to it) so you get the best fuel economy.  And cooler temperatures.  Good things for your engine.

Normally aspirated, turbo normalized, and turbo all work in a similar manner.

Why does this range from peak to 100 degrees ROP put you in the danger zone? For those who don't have engine monitors, what EGT value should we be leaning for? It seems like leaning to peak, and then enriching past 100 degrees ROP would nearly put you back at full rich?

[KSMooniac]

Full rich is likely to put you at 250 dF or more past peak.  You also won't get a recommended EGT value to lean to...those are variable based on a number of factors so that is why everything is referenced to the peak value on your first cylinder to peak, or last, depending on ROP or LOP settings.  Turbo installations might reference TIT instead.  

Once you get the education on this topic, you'll see the real value in an engine monitor...even a used non-primary monitor like a JPI EDM 700 (or 730 would be better) that you should be able to buy for $1500 can do the job.  Installation is tedious, but not technically difficult, so it is a great opportunity for some sweat equity if you're so inclined.  It can save more than that in reduced troubleshooting, or it could save your life some day as well.

[Pinecone]

On 10/30/2023 at 7:31 PM, ArrowBerry said:

 

Why does this range from peak to 100 degrees ROP put you in the danger zone? For those who don't have engine monitors, what EGT value should we be leaning for? It seems like leaning to peak, and then enriching past 100 degrees ROP would nearly put you back at full rich?

Because that is the range of potential detonation.  Which will destroy your engine.

You are OK, if you are at a low power setting though.

[A64Pilot]

On 10/25/2023 at 11:33 PM, Bolter said:

Most modern street cars are running very lean of peak until you demand power.  It helps with fuel econ and emissions. 

Lean of Peak is not a big deal, as long as you are doing it at the right time, as in not LOP during takeoff and high power climbs.  Cruise and descent are great opportunities for very efficient lean operation.  Some wise people have also demonstrated good effects on the engine by running LOP instead of ROP for the same % power.

Which Mooney has an O-320?  Is that the original engine of the M20A or B?  C, E, F G, and J are Lycoming 360's.

It has been said, but I cannot validate this, that the old fashioned leaning until rough, and then rich to smooth will put you LOP.  My J with the IO-360 would not get rough until LOP (verified with 4-point engine monitor).  With the Continental IO-550, it does not get rough until its so lean it might shut off.  

-dan

Modern cars don’t ever run LOP, they did back in the 70’s and 80’s but stopped I believe 20 years or so ago with I believe the Chrysler “lean burn” engine leading the pack, followed by Honda’s famous CVCC, then pretty much everybody else because of better fuel milage.

They don’t run LOP anymore due to emissions, LOP increases some emissions that’s hard to deal with (NOX)

https://en.wikipedia.org/wiki/Lean-burn#Honda_lean-burn_systems

Having said that stratospherically charged engines are I believe becoming more common, they sort of emulate some Diesel engines with their pre-combustion chamber, while the combustion isn’t LOP when the hot gases expand into the greater cylinder area it is

Mazda has developed a spark ignition gas Diesel engine, I know sounds wrong doesn’t it, but I think it’s the next evolution of the gas auto engine, the differences in a Diesel and spark ignition engine further decreases.

https://www2.mazda.com/en/next-generation/technology/

Finally the majority of stock aircraft flat engines just won’t run LOP, very few carbureted ones will, our Lycoming fuel injected IO-360’s are an exception, the overwhelming majority of engines when leaned to slight roughness then enrichened just enough to smooth out are being run very close to peak, right in the “red box”, without harm and have been done so for longer than most of us have been alive.

The rest of that leaning technique was to climb full rich and only lean when at cruise power, which if you obeyed the charts put you at a power setting that ANY mixture couldn’t hurt the engine, that’s why they weren’t detonated to death.

Our Grandfather’s leaning technique actually put you pretty darned close to an ideal cruise mixture if performance was a consideration, it’s only if your willing to give up some performance to achieve greater efficiency that LOP really becomes viable, now some will argue tgat you can run LOP and get better efficiency and not lose performance but that’s not true. There is only one mixture that you can get the most performance, Best Power mixture, any mixture other than it loses power either richer or leaner, the further away from best power the greater the performance loss.

TANSTASFL.

The only way to hurt a motor with the red knob is at high power, above 75% for Lycoming and 65% power for a Continental ( I can’t validate those numbers) but anyone who’s looking for efficiency won’t be even close to those power outputs, they are more likely to be in the 50’s % power output.

In my opinion, if one watches cyl head temp and never lets it go above 380 or so and shoots for 350 as a target, it’s very difficult to detonate an engine running 100 LL.

I’m talking non turbo engines here.

So at the power levels that you should be leaning at in my opinion it’s not really a concern, you can’t hurt the thing, and power levels that you can hurt the thing, you shouldn’t be leaning anyway, if you “run the numbers” as in how much fuel you can save by leaning in the climb, the fuel savings is minuscule. I don’t count maintaining take off EGT as leaning, in my opinion it’s maintaining mixture, not leaning.

Say you save 4 GPH by leaning in a climb, and you climb for 15 min, you will save 1 Gl, and I think 4 GPH isn’t realistic and most don’t climb for 15 min either, so 1Gl is probably optimistic, so just don’t lean in a climb, it’s just not worth it.

 

[Echo]

1 hour ago, A64Pilot said:

Modern cars don’t ever run LOP, they did back in the 70’s and 80’s but stopped I believe 20 years or so ago with I believe the Chrysler “lean burn” engine leading the pack, followed by Honda’s famous CVCC, then pretty much everybody else because of better fuel milage.

They don’t run LOP anymore due to emissions, LOP increases some emissions that’s hard to deal with (NOX)

https://en.wikipedia.org/wiki/Lean-burn#Honda_lean-burn_systems

Having said that stratospherically charged engines are I believe becoming more common, they sort of emulate some Diesel engines with their pre-combustion chamber, while the combustion isn’t LOP when the hot gases expand into the greater cylinder area it is

Mazda has developed a spark ignition gas Diesel engine, I know sounds wrong doesn’t it, but I think it’s the next evolution of the gas auto engine, the differences in a Diesel and spark ignition engine further decreases.

https://www2.mazda.com/en/next-generation/technology/

Finally the majority of stock aircraft flat engines just won’t run LOP, very few carbureted ones will, our Lycoming fuel injected IO-360’s are an exception, the overwhelming majority of engines when leaned to slight roughness then enrichened just enough to smooth out are being run very close to peak, right in the “red box”, without harm and have been done so for longer than most of us have been alive.

The rest of that leaning technique was to climb full rich and only lean when at cruise power, which if you obeyed the charts put you at a power setting that ANY mixture couldn’t hurt the engine, that’s why they weren’t detonated to death.

Our Grandfather’s leaning technique actually put you pretty darned close to an ideal cruise mixture if performance was a consideration, it’s only if your willing to give up some performance to achieve greater efficiency that LOP really becomes viable, now some will argue tgat you can run LOP and get better efficiency and not lose performance but that’s not true. There is only one mixture that you can get the most performance, Best Power mixture, any mixture other than it loses power either richer or leaner, the further away from best power the greater the performance loss.

TANSTASFL.

The only way to hurt a motor with the red knob is at high power, above 75% for Lycoming and 65% power for a Continental ( I can’t validate those numbers) but anyone who’s looking for efficiency won’t be even close to those power outputs, they are more likely to be in the 50’s % power output.

In my opinion, if one watches cyl head temp and never lets it go above 380 or so and shoots for 350 as a target, it’s very difficult to detonate an engine running 100 LL.

I’m talking non turbo engines here.

So at the power levels that you should be leaning at in my opinion it’s not really a concern, you can’t hurt the thing, and power levels that you can hurt the thing, you shouldn’t be leaning anyway, if you “run the numbers” as in how much fuel you can save by leaning in the climb, the fuel savings is minuscule. I don’t count maintaining take off EGT as leaning, in my opinion it’s maintaining mixture, not leaning.

Say you save 4 GPH by leaning in a climb, and you climb for 15 min, you will save 1 Gl, and I think 4 GPH isn’t realistic and most don’t climb for 15 min either, so 1Gl is probably optimistic, so just don’t lean in a climb, it’s just not worth it.

 

Thank you.  My vote for "best post of the week"  

[Shadrach]

3 hours ago, A64Pilot said:

Modern cars don’t ever run LOP, they did back in the 70’s and 80’s with I believe the Chrysler “lean burn” engine leading the pack, followed by Honda, then pretty much everybody else because of better fuel milage.

They don’t run LOP anymore due to emissions, LOP increases some emissions that’s hard to deal with (NOX)

https://en.wikipedia.org/wiki/Lean-burn#Honda_lean-burn_systems

Having said that stratospherically charged engines are I believe becoming more common, they sort of emulate some Diesel engines with their pre-combustion chamber, while the combustion isn’t LOP when the hot gases expand into the greater cylinder area it is

Mazda has developed a spark ignition gas Diesel engine, I know sounds wrong doesn’t it, but I think it’s the next evolution of the gas auto engine, the differences in a Diesel and spark ignition engine further decreases.

https://www2.mazda.com/en/next-generation/technology/

Finally the majority of stock aircraft flat engines just won’t run LOP, very few carbureted ones will, our Lycoming fuel injected IO-360’s are an exception, the overwhelming majority of engines when leaned to slight roughness then enrichened just enough to smooth out are being run very close to peak, right in the “red box”, without harm and have been done so for longer than most of us have been alive.

The rest of that leaning technique was to climb full rich and only lean when at cruise power, which if you obeyed the charts put you at a power setting that ANY mixture couldn’t hurt the engine, that’s why they weren’t detonated to death.

The only way to hurt a motor with the red knob is at high power, above 75% for Lycoming and 65% power for a Continental ( I can’t validate those numbers) but anyone who’s looking for efficiency won’t be even close to those power outputs, they are more likely to be in the 50’s % power output.

In my opinion, if one watches cyl head temp and never lets it go above 380 or so and shoots for 350 as a target, it’s very difficult to detonate an engine running 100 LL.

I’m talking non turbo engines here.

So at the power levels that you should be leaning at in my opinion it’s not really a concern, you can’t hurt the thing, and power levels that you can hurt the thing, you shouldn’t be leaning anyway, if you “run the numbers” as in how much fuel you can save by leaning in the climb, the fuel savings is minuscule. I don’t count maintains take off EGT as leaning, in my opinion it’s maintains mixture, not leaning.

Say you save 4 GPH by leaning in a climb, and you climb for 15 min, you will save 1 Gl, and I think 4 GPH isn’t realistic and most don’t climb for 15 min either, so 1Gl is probably optimistic, so just don’t lean in a climb, it’s just not worth it.

 

This was the a big part of the issue with VW AG’s “Diesel gate”. They avoided installing urea injection by running the cars rich during testing. However, during normal ops the production cars ran lean which delivered their staggering fuel economy (VW TDIs would deliver in excess of 60mpg on the Highway). They could pass NOx and they could deliver the promised performance…but they could not do both at the same time. 

All road going diesels run lean of stoic, but they use urea injected into the exhaust for NOx reduction. 
 

As for LOP climbs. 4gph is definitely realistic…initially.  The difference in WOTLOP and full rich fuel burn is more dramatic than that at low altitude. Full Rich at SL on a standard day for an IO360 is roughly 18.5gph. I have experimented with high power LOP at DAs of 0 or less and the best I can do is about ~85% and 11.x gph (rough numbers). All cylinders are >30LOP and CHTs >340. That’s a a roughly 40% reduction in burn from full rich for a 15% reduction in power.  It makes good sense for low altitude cruise but does not amount to much gain in climb efficiency, because the delta narrows as you climb and define takes significantly longer because power correlates directly to climb performance.  If I had a turbo, I would experiment with it, but I suspect high powered LOP may hampered by TIT limits.
Some of the TN’d Bonanza folks climb LOP but I suspect the higher compression engine yields better TIT margins.

 

[Shadrach]

On 10/24/2023 at 11:34 AM, RescueMunchkin said:

I see the term running LOP (Lean of Peak?) used a lot, but is there a writeup on how to find this mixture setting and fly safely with it applicable to M20F?

And how does running LOP work if the plane is also potentially manually wastegated turbo normalized?  Is most of the turbo's benefit the ability to fly higher to get stronger tailwinds, or are there other fuel efficiency benefits by flying at higher altitudes?

Thanks in advance!

Congratulations on your new to you F model.  I operate my F LOP frequently.  Operationally, it's quite simple but one should really gain a rudimentary understanding of what is actually taking place under the cowl to optimize both efficiency and safety.

It's for good reason that the articles linked below have been a staple for those looking for a deeper understanding of engine operations. They are the best "self study" starting point that I know of.  John Deakin passed in  2021 but he left a legacy of excellent aviation related content that is still relevant today.   I can offer more nuanced advice regarding how I operate my 67F but it will not be of much use to you until you have a foundational understanding.

https://www.avweb.com/features/pelicans-perch-63where-should-i-run-my-engine-part-1/

https://www.avweb.com/features/pelicans-perch-64where-should-i-run-my-enginepart-2-the-climb/

https://www.avweb.com/features/pelicans-perch-65where-should-i-run-my-enginepart-3-cruise/

https://www.avweb.com/features/pelicans-perch-66where-should-i-run-my-enginepart-4-descent/

 

[A64Pilot]

While I don’t know about the VW Diesel, but you cannot adjust mixture in a normal Diesel. Common Rails can do all kinds of “magic” though, vary timing, multiple injection events, even inject fuel in the exhaust stroke to burn in the Diesel particulate filter to burn it clean, called “regeneration” Common Rail is a complete game changer, took Grandpa’s old chug chug Diesel and made it into a hot rod.

They are arguably the ultimate LOP engine, because at all RPM’s and loads they take in a full volume of air, there is no throttle plate and therefore no vacuum in the manifold. While a spark ignition engine throttles both fuel and air, a Diesel only increases fuel to increase RPM / HP, so at part throttle they are exceedingly lean.

At idle their EGT is in the 200’s F, but as power increases so does EGT, often the limit of the power you can get out of a Diesel is when the pistons melt, take one ROP and they smoke like a train, you see that at Truck / Tractor pulls until the Turbo catches up with the fuel 

I used to love Diesels but all the emission equipment took a simple mechanical reliable beast and complicated the dickens out of it and reduced reliability, couple that with ULSD price and there just isn’t the advantage that there used to be.

I don’t know maybe the VW motor has a throttle valve? Wouldn’t surprise me as Diesels and gas motors are becoming more alike over time.

[ArtVandelay]

I lean based on fuel flow, at sea level FF is 18.8gph, rounded to 19, I subtract 1gph for every 1000’ of altitude, so at 6000’, target FF is 13.
This keeps me rich enough to prevent ignition issues, but not wasting a lot of avgas.
When taking off at high altitude airports, dialing in target FF is very quick and easy.

[skykrawler]

'......flying most efficiently'

Certainly don't want to use Carson speed.