Flying over square for better fuel economy, how far over can TSIO-360 safely go?

[Will.iam]

1 hour ago, A64Pilot said:

Why do you think your max fuel flow is 9.5? My NA 360 burns right at 20 on takeoff, and honestly more than 9.5 in normal cruise

If the engine is capable of 36” continuously, then it’s capable of 36” continuously, but obviously you don’t have to run the snot out of it if you don’t want to, but some feel the need.

We all operate oversquare at takeoff, fixed pitch guys even moreso, my little 140 is at 2300 and 30” at takeoff, R-1340 I cruised at 30” and 2000 RPM which is considered gentle, it’s max RPM from memory is 2250 and if memory is right it’s max MP at sea level is 36 

Oversquare with a boosted engine within POH is normal and actually probably more ideal, it after all is sort of the point of boosting.

Your Cirrus story is a good example of why to operate an engine IAW the POH, if he had, then he wouldn’t have had the problem. I know this never having seen a Cirrus POH.

The POH limits have been checked, outside of POH hasn’t, Listen to who built the airplane and not all the internet experts, if the POH values were wrong they would have been corrected long ago.

Or you can believe as so many do that all the manufactures are stupid and that aircraft have been operated safely for half a Century by pure luck

Ironically the cirrus poh does have LOP but i guess he missed the not WOT part or maybe he thought a little is good a lot is more better. 

[A64Pilot]

9 hours ago, Will.iam said:

Ironically the cirrus poh does have LOP but i guess he missed the not WOT part or maybe he thought a little is good a lot is more better. 

I believe pretty much everything made this Century does cover LOP, but you do lose power LOP, just remember (TANSTAAFL) and if you run high MP LOP your playing with fire. I am not saying you can’t safely, just as you can have fire inside of the house, with both it’s best to either have a very good understanding, or at least follow the rules (the POH), POH likely doesn’t cover high MP /LOP as you can easily damage an engine there, you can run LOP but it’s very possible if you get distracted or get it wrong it can cause damage, ROP is idiot proof, LOP is not at high MP

I do believe I have an understanding, yet I choose not to run LOP at high MP. I believe that’s why you have chosen 9.5 GPH as a limit, maybe you have read that, but you most certainly can limit power output by limiting fuel and by limiting to 9.5 GPH if you were a NA motor your limiting to about 142 HP, but a turbo is more efficient, I’d SWAG that a turbo may make 150 HP from 9.5 GPH, just a SWAG though. A turbo uses what is otherwise waste heat and therefore increases efficiency, at the cost of expense, complexity and weight TANSTAAFL

If you keep the power limited it’s hard to hurt anything and while I don’t know your engine it’s likely that 9.5 GPH may be a safe setting. It is for my 200 HP NA though it’s pushing harder than I run LOP, if I want to go faster than about 8 GPH will get me I flip to ROP, because I’m risk adverse.

 

Edited April 30, 2022 by A64Pilot

[Shadrach]

On 4/28/2022 at 7:34 PM, A64Pilot said:

There is nothing new about LOP, my Father would climb to 10 or 12 thousand and lean his 210 way back on long trips, 60 years ago, wasn’t called LOP, just “lean it out” most everyone with experience and not in a big hurry did, those in a hurry ran richer, usually about 100 ROP or more.

Then I don’t know about you guys but I was taught way back when to pull the mix knob until it got a little rough then slowly push it back in until it smoothed out.

Guess where that puts you in an engine capable of LOP? Yep pretty far into LOP. But as we were taught not to lean below 5,000 it didn’t hurt anything.

Lycoming doesn’t recommended LOP likely because it turns the engine into a dog and they don’t want that rep. Mooney likely didn’t either for the same reason, knocks off a bunch of speed at normal cruising altitudes when the throttle is fully open, and Mooney was selling speed.

Personally I run deep LOP most of the time, because I’m not in a hurry, but I do recognize the majority of my fuel savings comes from going slow, not from any huge increase in BSFC.

Leaning to rough and enriching to smooth works great with carbureted engines. It’s simple and produces the best BSFC of the engine’s available mixture ranges. Setting  power that way with a well conforming, injected engine results in a completely different mixture setting that unlike a carbureted engine will vary with altitude.  Roughness in most carburetted engine occurs around peak EGT at any altitude. Using my stock IO360 as an example, at low DA’s roughness starts ~100LOP which is not an efficient mixture setting in an NA engine. Doing that at altitude in my plane would yield a setting of about ~60LOP, also not the most efficient setting. Going slower with a higher BSFC is not very desirable

Edited May 1, 2022 by Shadrach

[A64Pilot]

So generally speaking as I know it’s a variable at what point is the highest BSFC obtained? 

I think BSFC can be changed of course with mixture, but not by as much as people think. I keep reading about saving 2.5 GPH by running LOP and don’t believe it at all, there is a savings but I’d be shocked if it were even close to 10%, where I think these big numbers come from is speed loss, people aren’t comparing LOP to Peak or ROP at the same speed.

Personally I run LOP more for a cleaner combustion chamber and plugs than anything else, and if I’m going out to eat breakfast etc which is most of my flying now, why be in such a hurry? So I slow down and enjoy the flight, engine runs cooler, engine is quieter, the bumps smoother and as it’s a short flight time difference is irrelevant, basic OFO flying.

Point of bringing up the pull until she starts to stumble and then back to it smooths out is that in most injected engines it puts you LOP, so anyone doing that has always been running LOP, just before it became fashionable only a few even knew they were LOP, even fewer cared. My 540 it put me about 25 LOP.

Our Lyc 360’s are an anomaly, most injected engines won’t run so well LOP, some won’t run LOP well at all, even with fine wires and Gami injectors. My 540 for instance Gami injectors made almost no difference, fine wires made more difference, but the most LOP you could get was about 25F, my 360 will run smooth until there is essentially no power, still smooth though and it’s stock. It’s the LOP poster child.

Edited April 30, 2022 by A64Pilot

[jetdriven]

15 hours ago, A64Pilot said:

Why do you think your max fuel flow is 9.5? My NA 360 burns right at 20 on takeoff, and honestly more than 9.5 in normal cruise

If the engine is capable of 36” continuously, then it’s capable of 36” continuously, but obviously you don’t have to run the snot out of it if you don’t want to, but some feel the need.

We all operate oversquare at takeoff, fixed pitch guys even moreso, my little 140 is at 2300 and 30” at takeoff, R-1340 I cruised at 30” and 2000 RPM which is considered gentle, it’s max RPM from memory is 2250 and if memory is right it’s max MP at sea level is 36 

Oversquare with a boosted engine within POH is normal and actually probably more ideal, it after all is sort of the point of boosting.

Your Cirrus story is a good example of why to operate an engine IAW the POH, if he had, then he wouldn’t have had the problem. I know this never having seen a Cirrus POH.

The POH limits have been checked, outside of POH hasn’t, Listen to who built the airplane and not all the internet experts, if the POH values were wrong they would have been corrected long ago.

Or you can believe as so many do that all the manufactures are stupid and that aircraft have been operated safely for half a Century by pure luck

If it’s not in the limitations section it’s not a limitation. That said I stay within the factory graphs, and those allow 2000 RPM at 26” of MP and also says “lean as far as you want to  for smooth operation”.  Ours is smooth to 75 LOP. Efficiency below about 25 gets worse quickly. 

[PT20J]

19 minutes ago, jetdriven said:

If it’s not in the limitations section it’s not a limitation. That said I stay within the factory graphs, and those allow 2000 RPM at 26” of MP and also says “lean as far as you want to  for smooth operation”.  Ours is smooth to 75 LOP. Efficiency below about 25 gets worse quickly. 

EXACTLY. It’s an interesting exercise to see how lean an engine will run, but it’s not operationally useful.

[exM20K]

18 hours ago, Will.iam said:

Actually no very far from WOT actually because Of my over square question / fear originally stated. For example, 25”mp 2500rpm and 9.5 puts me at 25 F LOP. Now if i increase MP to say 28” then LOP goes to something like 50 LOP and pushing to 31” MP and things get rough as I’m now down to something like 75 or 80 degrees LOP since i kept the fuel flow at 9.5 and rpm at 2500 for each MP change

I think I understand what you’re trying to do: LOP, power is a function of fuel flow only(ish), so is there efficiency to be gained by spinning stuff slower.  Do I have that about right?  I choose to target lower TIT and acceptably smooth operation. 

I flew my 231 the same way I do the acclaim: set power, lean to richest cylinder is 50* LOP, then add back throttle for the desired fuel flow. I run 2400 rather than 2500 because it gives me much lower TIT, which I believe to be a result of fewer combustion events per unit of time.  Lower RPM advances the timing a bit, so setting aside friction losses, higher rpm at the same fuel flow should produce more power.  But at the end of the day, it just doesn’t make a big difference in fuel burn when choosing what setting for a given fuel flow LOP.  I choose lower TIT vs smooth operating when I select 2400 vs 2500 rpm. A good dynamic balance will cure the vibes pretty well, and maybe my exhaust system lasts a bit longer at 2400.

@carusoam speed and efficiency are for sure not mutually exclusive.  My 90% trip is about 750 NM.  16.5 GPH LOP is easy.  21GPH ROP, even with the extra 10-15 knots, is cutting it pretty close.  Fuel stops suck, which is part of the reason a low end turboprop is unsuitable for my trip.

-dan

[Shadrach]

7 hours ago, A64Pilot said:

So generally speaking as I know it’s a variable at what point is the highest BSFC obtained? 

I think BSFC can be changed of course with mixture, but not by as much as people think. I keep reading about saving 2.5 GPH by running LOP and don’t believe it at all, there is a savings but I’d be shocked if it were even close to 10%, where I think these big numbers come from is speed loss, people aren’t comparing LOP to Peak or ROP at the same speed.

Personally I run LOP more for a cleaner combustion chamber and plugs than anything else, and if I’m going out to eat breakfast etc which is most of my flying now, why be in such a hurry? So I slow down and enjoy the flight, engine runs cooler, engine is quieter, the bumps smoother and as it’s a short flight time difference is irrelevant, basic OFO flying.

Point of bringing up the pull until she starts to stumble and then back to it smooths out is that in most injected engines it puts you LOP, so anyone doing that has always been running LOP, just before it became fashionable only a few even knew they were LOP, even fewer cared. My 540 it put me about 25 LOP.

Our Lyc 360’s are an anomaly, most injected engines won’t run so well LOP, some won’t run LOP well at all, even with fine wires and Gami injectors. My 540 for instance Gami injectors made almost no difference, fine wires made more difference, but the most LOP you could get was about 25F, my 360 will run smooth until there is essentially no power, still smooth though and it’s stock. It’s the LOP poster child.

for normally aspirated engine Max BSFC occurs between peak and 25° LOP EGT.

low compression turbos have a wider BSFC range at high MP.

The most efficient way to run a NA injected engine is as close to peak as CHTs will allow. This yields the highest output for a unit of input.  

Same is true of a Turbo. However, you have the benefit being able to additional MP to the equation if needed for cooling (all other things being equal). If you had unlimited MP you could theoretically run a turbo at max power within the max BSFC range on the lean side of peak and have a large fuel savings.

[A64Pilot]

I though max BSFC would be close to peak, but on the lean side slightly, and 25 degrees is compared to EGT is slight, 25F is what about 2% of EGT? 

 

[PT20J]

Here's a plot from an old Continental IO-550 manual I got from APS. 

[A64Pilot]

Near as I can tell the Conti graph doesn’t show EGT, but one can assume max power is about 150 ROP, so it seems to indicate max efficiency is roughly the same number of degrees max power is, so roughly 150 LOP?

Conti and Lyc are different, but that’s a large spread

[PT20J]

EGT is the second curve from the top. Min BSFC is about 50F LOP for a drop of about 15 bhp from peak EGT. The EGT curve isn't very sharp at the peak. This is mostly an indication of poor mixture distribution with the cylinders peaking at different fuel flows. Even with perfect mixture distribution though, the EGT curve will still be rounded somewhat at the peak due to chemical dissociation at high temperatures generated by a stoichiometric mixture. Dissociation of the combustion products frees up oxygen and is what allows more fuel to be added and burned causing the maximum CHT to occur somewhat rich of peak. Further addition of fuel slows the burn rate reducing temperature, but results in more molecules in the cylinder which increases power and that's why the max power occurs at a mixture slightly richer yet. Adding more fuel beyond max power slows combustion with a greater effect on power than the addition of additional substance, so the power and temperature both fall off. 

[carusoam]

Why LOP is disappointing for some….

 

Simplified to using an NA engine…. For conversational purposes…

Then adding back some TC and TN’d points…

 

For each 0.1gal of FF leaner than peak… is exactly 0.1g of fuel not being used to produce power…

So… being 50°F LOP… has actually removed a lot of hp in the process… (surprised?)

Compared to 50°F ROP… where no fuel has been taken away from HP production… (not surprised?)

 

So… yeah going 50°F LOP is slow…. for NA engines…

A well balance IO550 can achieve near 100°F LOP (around 5k’msl) before the engine just shuts off…less and less power, no shakes, no get rough, just silence…. turn the knob to the right again… and it relights just as easily…. 
 

We fly for speed… going deep LOP… is mostly a technical discussion…

Imagine teaching lean til rough… in an Ovation…   And rough never happens… then enrichen until the noise comes back… at near 100°F LOP… Enrich until Vs = 0 

Fantastic mileage… slow flight…

If you don’t like how the power drops off… select an altitude where max MP is 65%bhp… lean to peak… enjoy the flight… CHTs will be nicely maintained there as well… Go O!

Flying above 10k’ AGL has the advantage of glide time/distance… (when you can…)

Rough numbers for the O1… 175kts ROP, 165kts LOP and about 2gph difference… (LOP by a few degrees, not deep)

Curvy balanced intake pipes make the difference…

balanced fuel injectors make sense to match the curvy pipes…

fine wire plugs are icing on the cake…

Dynamic balance for the prop to smooth everything out…

 

Lycoming has all kinds of curvy intake pipes… they just didn’t make it into the Mooney fleet.

 

The advantage of having a TC’d engine…

The same can be done as the NA engine… but at a much higher altitude…. Using the same 65%bhp…

More can be done as FF can be kept high and burned to produce power… while using excess compressed air can be used to cool EGTs and ITTs…

So… higher than 65%bhp can be used safely… from a TIT point of view… CHT, and EGT…. 
 

The higher %bhp comes with the natural challenge of getting rid of the extra heat of so many extra GPHs being burned….

There is only so much external cooling available… and the thinner the air at altitude makes a big difference….

So…

We are going to find…

Flying at high power settings…

1) is safe when executed properly…

2) slightly lower cost when LOP…

3) converts all of the 100LL to power, none tossed out to the environment…

4) Most often seen executed in Mooneys with Continental engines…

5) Fastest Mooney speeds occur in this regime… (just add more tail wind…)

6) CHT control is more challenging because of the high power, and thin air combination….

7) People like to target 380°F and lower for CHTs… to nicely get to TBO on one set of cylinders…

8) Some days you can operate at high BHP%… and other days, you can operate at a more moderate BHP%…

9) Collect your data religiously… determine your best leaning techniques… practice often…

10) Anyone have a CHT vs TBO graph…? With a second line for 1/2 way to TBO… and worst case of 1/3 way to TBO…?

 

 

How fast do you want to fly?

How many sets of cylinders do you want to afford to fly fast?

PP thoughts only, all stuff that can be read around here daily…

Go Flaming Dragon Mode!

Best regards,

-a-

[A64Pilot]

ROP power drops slightly, but look at corresponding drop in cyl head temp

I disagree that a Conti runs better LOP, my 360 is smoother than my IO-520 was with Gami injectors and fine wires. But if you want to fly a smooth LOP motor, get a Supercharged Radial

High power LOP in either a NA or boosted motor can be risky

[Shadrach]

20 minutes ago, A64Pilot said:

ROP power drops slightly, but look at corresponding drop in cyl head temp

I disagree that a Conti runs better LOP, my 360 is smoother than my IO-520 was with Gami injectors and fine wires. But if you want to fly a smooth LOP motor, get a Supercharged Radial

High power LOP in either a NA or boosted motor can be risky

I’ve been operating my stock IO360 high power LOP for almost 20years. It appears to love it.  What is the risk? Temps are well controlled, plugs stay clean, belly does not accumulate soot and I’m not dumping an extra 4-6 gals through the engine every hour. 

[Cruiser]

I ran LOP in my M20J - IO360 Lycoming and got a reliable 148-150 KTAS. There was a slight roughness because of the fuel flow between cylinders was always slightly different. The pesky #2 cylinder was always richer than the other three. 

I ran LOP in my M20R IO550G Continental and got a reliable 168- 170 KTAS. That was always smooth, sometimes with 0.0 difference between six cylinders. 

In the M20J I could depend on 16 to 17 mpg but with the two extra cylinders in the M20R the best efficiency was 13.5 mpg. 

Physics is science, Fuel, Air, Mixture are all known elements of running an internal combustion engine. My (or your) believes of how they work does not change the science. 
Mooney's are the most efficient airplanes every manufactured.  Running as BSFC fuel flow is the most efficient way to operate them. 
and that is all I have to say about that. 

[A64Pilot]

2 hours ago, Shadrach said:

I’ve been operating my stock IO360 high power LOP for almost 20years. It appears to love it.  What is the risk? Temps are well controlled, plugs stay clean, belly does not accumulate soot and I’m not dumping an extra 4-6 gals through the engine every hour. 

Define high power? I believe you mean actually high MP, cause LOP high power isn’t possible, not at normal cruise altitudes, high in my mind being above 75%, cause Lycoming defines 75% and below as cruise power.

The problem is for whatever reason you let it get too rich, just as a guy who’s at TO power climbing and wants to save .5 gallons of gas and overleans.

‘I’m not saying don’t do it, it’s your airplane, but if I’m in a hurry I won’t, one reason because it’s not as fast as ROP and I’m in a hurry and secondly because how ever small, there is some risk.

What do Continental’s FADEC engine do at high power?  FADEC ought to be able to manage perfectly, better than any person.

‘Bottom line your not changing my mind and I’m not changing yours anymore than I can get the guy who has smoked for 50 years to quit, cause he’s done it for 50 years and he’s fine.

[A64Pilot]

3 hours ago, Shadrach said:

I’ve been operating my stock IO360 high power LOP for almost 20years. It appears to love it.  What is the risk? Temps are well controlled, plugs stay clean, belly does not accumulate soot and I’m not dumping an extra 4-6 gals through the engine every hour. 

Really, your saying speed is the same but fuel burn is 6 GPH less?

[PT20J]

The concern about running LOP at "high" powers is probably fear of detonation. Detonation is caused by heat. High cylinder pressures heat the mixture by compression and rapid burning of the charge causes the end gas to further heat by the compression by the advancing flame front. If the heating gets to the point of self ignition, the end gas combusts very rapidly with the pressure rise typical of detonation. 

John Deakin, before he quit flying after his stroke, used to cruise his turbo-normalized Bonanza LOP at 80+% power with CHTs at 380F or below. I have no idea what the long term effects may have been, good or bad. I understand some Cirrus guys do this, but I haven't hung out on the Cirrus site for a long time since I'm not flying a Cirrus any longer. I asked Mike Busch and he didn't have an opinion stating that he runs his 310 LOP at low (65% or less) powers because, "I'm a longevity guy, not a speed guy." I would really like to know the long term effects of "high" power LOP if anyone has a source of data rather than opinions.

Skip

[Shadrach]

2 hours ago, A64Pilot said:

Really, your saying speed is the same but fuel burn is 6 GPH less?

At WOTRAO at a a DA of 1500’? Yes. My options are pretty much full rich or >30LOP. 

Edited May 1, 2022 by Shadrach

[A64Pilot]

WOTRAO? WOT is usually wide open throttle, RAO?

You fly around at 1500, hair on fire?

How much speed loss LOP?

Most of us I believe fly around when traveling and clouds no issue roughly 7,500 plus or minus, it’s the point most NA airplanes go quickest with least fuel flow, above that and you usually slow down , below that and fuel consumption gets out of hand and it puts you at full throttle and 2500 RPM real close to 75% power which I believe is max recommended cruise from Lycoming. Charts assume ROP, so less power of course if LOP. But below 7,500 or so you need to reduce throttle to stay below 75% power.

Lycoming has published for max engine life they recommend 65% max cruise, but I don’t have the reference handy.

Be nice if Lycoming would publish LOP charts, maybe they do, but I’ve not seen them

My motor noise / vibration seems best roughly 2300

Going to breakfast and back this morning was 1000 out, 2500 back due to low clouds, 23 squared and 7.5 GPH 130 kts, put me 50C LOP or 122F. If LOP I like deep LOP, just more cushion is all, plus I close cowl flaps and cyl head temp is 1/3 into the green, may sound stupid, but engine seems to like it, plugs, oil stay clean.

36NM distance, 15 min no need to climb and really not need for speed, neighbor who runs his 550 Bonanza wide open cause he has to be the fastest, was 3 min less time to breakfast.

 

found it

 

Edited May 1, 2022 by A64Pilot

[Shadrach]

13 minutes ago, A64Pilot said:

WOTRAO? WOT is usually wide open throttle, RAO?

You fly around at 1500, hair on fire?

How much speed loss LOP?

Most of us I believe fly around when traveling and clouds no issue roughly 7,500 plus or minus, it’s the point most NA airplanes go quickest with least fuel flow, above that and you usually slow down , below that and fuel consumption gets out of hand and it puts you at full throttle and 2500 RPM real close to 75% power which I believe is max recommended cruise from Lycoming. Charts assume ROP, so less power of course if LOP. But below 7,500 or so you need to reduce throttle to stay below 75% power.

Lycoming has published for max engine life they recommend 65% max cruise, but I don’t have the reference handy.

Be nice if Lycoming would publish LOP charts, maybe they do, but I’ve not seen them

My motor noise / vibration seems best roughly 2300

Going to breakfast and back this morning was 1000 out, 2500 back due to low clouds, 23 squared and 7.5 GPH 130 kts, put me 50C LOP or 122F. If LOP I like deep LOP, just more cushion is all, plus I close cowl flaps and cyl head temp is 1/3 into the green, may sound stupid, but engine seems to like it, plugs, oil stay clean.

36NM distance, 15 min no need to climb and really not need for speed, neighbor who runs his 550 Bonanza wide open cause he has to be the fastest, was 3 min less time to breakfast.

RAO= Ram Air Open. The DA at my 700’ field is often -3000’ or less for several months out of the year.  Sometimes I don’t see SL atmosphere until 4000msl. So yeah, I guess I do.

Edited May 1, 2022 by Shadrach

[carusoam]

Four cylinder engines are nicely balanced… naturally.  Mooneys didn’t get a four cylinder Continental engine for comparison…

Things get more challenging when the throttle plate is closer to one set of cylinders than the last…

Log style vs. curvy flow balanced intakes…

expect the Log Style to be nicely balanced for ROP over a good range of operating conditions…

The engine data will show which cylinders are more ROP than the others…

it is in the plenty good enough category…

 

Lycoming has curvy intakes and electronic ignition in their six cylinder experimental category….

It would be really cool… to go to the Mooney store… and spec out your new Long Body…

Check the boxes for…

flow balanced cylinders… no valve issues…

tuned fuel injectors…

Fine wire plugs…

Electronic ignition…

 

…and fly often… 

 

Happy Sunday,

-a-

 

 

[Shadrach]

Lycomings chart.

[Shadrach]

On 4/29/2022 at 7:23 AM, A64Pilot said:

Even if you find charts showing you what you want, there are differences in aircraft and engines. If you match speed as close as you can you remove most variables.

Do the low RPM test first, then the higher one and use the A/S you got from the low RPM test as of course you can go faster with higher RPM. First test point use the bottom of the green, second pick the smoothest RPM, if there is a significant difference your on to something, if it’s small, then maybe it’s not worth it. Have to have smooth air.

I’m of the opinion that smooth is easier on the airframe, the avionics and less tiring on the people and probably easier on the engine too.

It helps if you have altitude hold, smooth air of course and hit different test points on the same flight to remove any differences in atmosphere, you can correct for DA but why bother, it doesn’t take long, but be as precise as you can, let speed level off. Relean to a set point like say 25 LOP don’t use a set temp as mixture will change with RPM if you do.

I did several test points on my IO-540W1A5D in my Maule comparing 25 LOP to Lycoming’s recommended 50 ROP. I had Gami injectors and fine wire plugs, newly overhauled Mag, new ignition harness and engine 200 SMOH with new Millenium cylinders. Try as I could but the 540 just wouldn’t go leaner than 25 LOP and stay smooth. I did the testing between 10 an 12 thousand as the Maule was fastest between those altitudes at 135 true, ROP, full throttle, RPM in middle of the green at 2200

Anyway what I came up with was two fold, first I lost more than 10 kts LOP, I don’t remember the exact number it was years ago, but secondly there was very little difference in fuel consumption if speed was identical. of course I was full throttle LOP but pulled back ROP.

Now there are other reasons to run LOP, I almost always cruise my Mooney LOP unless I’m in a hurry and maybe the Lyc 360 works better LOP than the 540, it certainly will run smooth much, much deeper LOP than the 540, but I suspect the majority of fuel savings from LOP comes from speed reduction. 

If low ITT is your goal, I believe you’ll find the lower ITT will occur at higher RPM and lower manifold pressure, but I don’t fly a turbo so that’s a guess.

If you conduct the testing please report back, whatever the results they will be interesting.

What is the operational reasoning for operating a NA engine that lean at those altitudes. I cannot think of an operational reason to run anywhere near 25° LOP at 10k or above with a NA engine..