Leaning in flight - is it better, really?

[Fix]

Interesting topic, since I'm trying to get my SB engine to run more smooth on LOP.
Maybe I don't do it correctly when leaning to LOP side, but I'm pretty sure that I'm close to doing it right.

I have an -SB engine and use 25-27" and 2500rpm and use 9.6g/h. (~ 60% power)
When I checked with my engine monitor I'm ~20 LOP but have some roughness.
This is from 2000feet to 5000feet.

Will test more soon as my aircraft is ready from annual.
Want to test 65% with 10.4g/h

Since I more or less just bought my M20K 252 I'm still learning.

My goal is to have a smooth running engine at LOP.
Have FireWire plugs, checked for correct gap.

I'm also installing a SureFly at this annual, (Right Mag) and that was the mag that was running most rough for me,

[Ragsf15e]

1 minute ago, Fix said:

Interesting topic, since I'm trying to get my SB engine to run more smooth on LOP.
Maybe I don't do it correctly when leaning to LOP side, but I'm pretty sure that I'm close to doing it right.

I have an -SB engine and use 25-27" and 2500rpm and use 9.6g/h. (~ 60% power)
When I checked with my engine monitor I'm ~20 LOP but have some roughness.
This is from 2000feet to 5000feet.

Will test more soon as my aircraft is ready from annual.
Want to test 65% with 10.4g/h

Since I more or less just bought my M20K 252 I'm still learning.

My goal is to have a smooth running engine at LOP.
Have FireWire plugs, checked for correct gap.

I'm also installing a SureFly at this annual, (Right Mag) and that was the mag that was running most rough for me,

The gami spread is as important as your good ignition.  What is your spread?  If you haven’t checked that, likely that’s where you should start.  Cylinders need to peak pretty close together (at about the same ff).

Mine runs well at 65% lop.  I’ve been using 30”, 2300, 10.4 and seeing about 141kias at all altitudes.

[Fix]

6 minutes ago, Ragsf15e said:

The gami spread is as important as your good ignition.  What is your spread?  If you haven’t checked that, likely that’s where you should start.  Cylinders need to peak pretty close together (at about the same ff).

Mine runs well at 65% lop.  I’ve been using 30”, 2300, 10.4 and seeing about 141kias at all altitudes.

Sorry...

I get all from 0.3 to 0.6 depending on when I do it.
Guessing that I have OK Gami Spread, and it's my ignition that is the issue.

Anyway, we have checked different things, and if it don't work as I hope after a SureFly and carefully timed left magneto, than I will try to get Gami Injectors.

[kortopates]

Sorry...

I get all from 0.3 to 0.6 depending on when I do it.
Guessing that I have OK Gami Spread, and it's my ignition that is the issue.

Anyway, we have checked different things, and if it don't work as I hope after a SureFly and carefully timed left magneto, than I will try to get Gami Injectors.

Ignition would have to be absolutely terrible to prevent getting good repeatable sweeps. It shouldn’t be a factor at peak. It’s much more likely to be from technique or poor mixture - but 0.6 is far from poor.


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[Will.iam]

Also extremely important to make sure you have no air induction leaks. When I first got my gami injectors I did not realize I had a small induction leak on #3 cylinder and when I fixed that then my number #3 cylinder was outside .5 spread and I had to get a replacement gami injector. This was maddening as the air leak didn’t really show itself at low altitudes but the higher you go the more the turbo works and the bigger the pressure differential from ambient and that air leak would in fact make that cylinder richer which when flying lop would mean that cylinder would creep closer to peak as I would fly higher and thus the cht on the cylinder would rise up especially with the thinner air at higher altitude. So to save you some frustration make sure you have no upper deck air leaks before you send that data to gami. Garbage in gets you garbage out. 

[Will.iam]

17 hours ago, Ragsf15e said:

The gami spread is as important as your good ignition.  What is your spread?  If you haven’t checked that, likely that’s where you should start.  Cylinders need to peak pretty close together (at about the same ff).

Mine runs well at 65% lop.  I’ve been using 30”, 2300, 10.4 and seeing about 141kias at all altitudes.

Interesting, I see 145kias at pattern alt 2k feet 160kias at 12,5k feet and 185kias at 22k feet all on the same 10.4 gallons per hour. 

[Ragsf15e]

8 minutes ago, Will.iam said:

Interesting, I see 145kias at pattern alt 2k feet 160kias at 12,5k feet and 185kias at 22k feet all on the same 10.4 gallons per hour. 

I think you mean ktas.  Yes my true airspeed is much higher too, maybe ~8 knots higher than you indicate above.  But my kias (indicated) is right around 141kias.

[Will.iam]

1 hour ago, Ragsf15e said:

I think you mean ktas.  Yes my true airspeed is much higher too, maybe ~8 knots higher than you indicate above.  But my kias (indicated) is right around 141kias.

Yes you are correct. I miss that. 

[Fix]

9 hours ago, Will.iam said:

Interesting, I see 145kias at pattern alt 2k feet 160kias at 12,5k feet and 185kias at 22k feet all on the same 10.4 gallons per hour. 

I also have around 140ktas +/- 5kt at 1000-4000ft at 26"/2500 9.8g/h.
 

[Pinecone]

On 4/16/2025 at 9:28 PM, DCarlton said:

I read the article.  Appreciate the technical details.  However, if I think back to my C-152 training days, I believe I was trained to lean the mixture until the engine started running rough and then put a few turns on the mixture control until it smooths out.  If you start with that basic procedure for cruise in a normally aspirated IO-360, it seems like you would always be below the red fin on the LOP side.  Keeps it simple; no EGT or Engine monitor required.  Then richen to taste with the monitor if you want more HP or to up your engine management game.  Am I missing any important nuggets?     

The problem is, some engines start running rough as soon as they go LOP, so you slightly richer can put them right in the red area.  And your richen for taste for higher HP will surely put you in the red area.

If you are below 65% power, not a big deal, but you need to be sure you are there.

[jlunseth]

The other issue is uneven fuel flows. If the fuel flows at each of the cylinders are far enough apart and you follow the old advice to lean to roughness and then enrich back to smoothness, some of the cylinders may be in the "red box" while others are sufficiently lean. If you run the engine long enough at that kind of setting you are likely to see the need for a top overhaul replacing those cylinders. Again, if you run at or under 65% it does not matter.

[airmocha]

On 3/15/2025 at 3:05 PM, jlunseth said:

I have an LB and a JPI930 but in all other respects about the same as yours. I don't think you are running ROP at all at 11 GPH and 29". In my engine, ROP at that MP and 2450 RPM would be 13+ something GPH to get to about 125 degrees ROP.

Maybe the problem is, what makes you think you are running LOP at that setting? 

Here is what I suspect. I don't know your engine monitor, but using my JPI the standard instructions are to start by running the engine well on the ROP side, put the monitor in lean of peak mode for leaning, and then lean out until the monitor tells you that you are LOP. Select your degrees LOP from the monitor and there you are. The problem is that this method is completely wrong for the 231. Lean of Peak and Rich of Peak are air/fuel ratio settings. They are not power settings although they can be used to make a power setting. The leaning mechanism in the monitors I am familiar with are all algorithms, in other words, our aircraft have no sensors that directly measure the air/fuel ratio the engine is running at.

The algorithms I am familiar with all make the same assumptions, (1) that you start on the Rich of Peak side, and (2) that while you are leaning the fuel all other things remain equal, most importantly, that the manifold pressure remains where you set it when you started your leaning process. This works in the 252 and other turbo Mooneys that have truly automatic wastegate controllers that maintain MP where you set it while you lean out the fuel. The problem with the 231, even with the Merlin, is that MP does not remain where you set it if you start reducing the fuel flow. The Merlin is a differential controller, not a density controller. There are several things going on. One, there is an interlink in the TSIO360 engine so that if you set a power setting of, let's say, 30" and 13.3 GPH, and then decide you want to slow to approach speed, you can pull the MP back and the interlink automatically reduces the fuel flow to maintain roughly the same air/fuel ratio that you had at 30/13.3. Notice that when you do this the air/fuel ratio is not changing, you are still running ROP even though the EGTs have all dropped from their starting point. This interlink in my experience does not work as effectively when you pull the fuel back as it does when you pull the MP back, but it does work. So the MP is dropping as you lean the fuel. Second, as the engine begins to produce less power the turbo produces less compression, further causing the MP to drop as you pull the fuel back. These things are causing you to violate the basic assumption of the leaning algorithm - that MP stays steady while fuel flow is reduced, thus changing the air/fuel ratio from a rich setting to a lean setting. In short, if you do your leaning this way all you have done is reduce power, but you have done little to change the air/fuel ratio. The engine monitor will most likely detect a drop in EGT in all the cylinders, which is their signal to tell you that you are running lean of peak when the monitor really has no idea where you are running any longer.

We just did a lean test on my new engine. The proscribed method is to start at an approximately 65% Rich of Peak setting, then slowly lean in increments of .3 GPH and record the EGT's on each cylinder. We chose 24.8 MP, 2400 RPMs, and 9.5 GPH, which I know from experience is a ROP setting. A move of .3 GPH did not change the MP much but a move of .6 changed it by a few tenths, enough that for about every two moves of .3 GPH we had to bump the MP back up a little. If you make a relatively big fuel move, like 11 GPH to 9.5 GPH you will get a fairly large MP decrease - on the order of 1" or more - and that invalidates the lean test you think you are running.

If it helps - if I want to fly at least 125 degrees ROP in my engine at an MP of 29", I need a fuel flow of 13.3 GPH to 13.5 GPH. A setting of 11 GPH is going to be a LOP setting most likely, but not a very LOP setting at 29". At 29" you are probably just a few degrees LOP, pretty close to peak. Anything in the 12's is going to be a Peak setting or worse, around 50 degrees rich of peak.

There is more to it, but based on what I would see in my engine at those power settings your 9.5 setting is probably a 60-65% power LOP setting and your 11 GPH setting is probably not lean of peak at all or if it is, it is just barely lean of peak, but it is not rich of peak. You are running too close to peak.

I have an '85 231 with the Trophy 262 -MB conversion, GAMIs, fine wire plugs, and a new JPI 830, if I recall the number correctly. 

I'm embarrassed to admit I've never thought about the phenomenon you describe so well here, where as I lean LOP, the MP and therefore the EGTs/TIT drop, lowering my power setting by roughly 10%.

Are you saying the 252's -MB engine shouldn't do this? And if it does, are we to open throttle as we lean, to hold MP?

I'm afraid I've been underleaning all this time, and I'm sure glad I've been careful to start around 65% or less and go to 50 LOP or more.

[kortopates]

I have an '85 231 with the Trophy 262 -MB conversion, GAMIs, fine wire plugs, and a new JPI 830, if I recall the number correctly. 
I'm embarrassed to admit I've never thought about the phenomenon you describe so well here, where as I lean LOP, the MP and therefore the EGTs/TIT drop, lowering my power setting by roughly 10%.
Are you saying the 252's -MB engine shouldn't do this? And if it does, are we to open throttle as we lean, to hold MP?
I'm afraid I've been underleaning all this time, and I'm sure glad I've been careful to start around 65% or less and go to 50 LOP or more.

What John described for the 231 with his manual pneumatic waste gate controller doesn’t apply to your -MB with your automatic hydraulic controller. Its holds MAP pretty well as you lean. But if you’re leaning to 50F LOP at 65% power you are over leaning. But in reality it’s really unlikely you’re able to get that lean without roughness. I’d encourage you to review your downloaded data to see where it’s really at.


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[airmocha]

9 hours ago, kortopates said:

What John described for the 231 with his manual pneumatic waste gate controller doesn’t apply to your -MB with your automatic hydraulic controller. Its holds MAP pretty well as you lean. But if you’re leaning to 50F LOP at 65% power you are over leaning. But in reality it’s really unlikely you’re able to get that lean without roughness. I’d encourage you to review your downloaded data to see where it’s really at.


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For sake of understanding, if I didn't have an MB, would I need to open throttle to hold MAP constant while leaning? This whole thing sounds like a chicken/egg situation I find mind boggling. Blue screen of death here! Lol

Thanks to Brian Kendrick of Mooney Support on San Marcos, I can lean that far, though only that far, without what I perceive as "roughness" - but I admit my sense of such is highly subject to expectations.

 

My EGTs stay generally within 10 or 15 degrees of each other from near to beyond peak, and yes, my MAP does shift a little, but I always attributed the drop in % power to the fuel flow reduction alone, and never considered that my turbo is loading somewhat when I lean and rob it of all that energy at the turbine. That's where I get back to the chicken/egg and wonder where it ends?

If I start with 32/2500 or so in the climb (I actually see slightly higher TIT (yes at less fuel flow) at 30/2500, for reasons I don't yet fully understand), and throttle back to around 75% power (maybe, what, 26-28"/2300?), when I hit "LOP" on my JPI, I see peak TIT at very nearly the 1650 redline (yes, I do try to hurry through that setting), and end up at about 65% power. I don't recall how much my MAP drops, but i know it does some. 

I get enough "go fast on glass" at work,  so I'm an "efficiency" guy and "steam gauges" nostalgic, so I don't often run it that hard, however. I much more often throttle back further, to maybe just an inch or two over square, to about 55% power, and try to get to 50 LOP without roughness or a big EGT spread, and witness a peak TIT under 1600, and settle in to enjoy my beautiful old airplane at around 45% bhp.

I've only had it for about 200 hours over 5 years now, and just got the JPI/GAMIs to go LOP last year, but it seems OK with what I'm doing. No cylinder or turbo issues yet on a 15 years/500 hours old engine. Course I used to always run at least 50 ROP, and even cooler if I was pulling more than 65% bhp.

I'm just not a fan of marriage to fuel flows. Atmospheric and engine conditions just change too much too often for that. I think i understand the principles at work (turbo de-bootstrapping from leaning LOP excluded, lol) and pay very keen attention to TIT, hottest/leanest/richest cylinder, distances from their peak, and EGT spreads, and try to make/keep my hottest/leanest/richest cylinder safe,  with no outliers among the other 5 farther from danger, whether I'm operating LOP for efficiency at lower power, or ROP for speed at higher power.

 

Hope this makes sense - I'm not preaching...just disclosing. If I'm doing something bad or wrong, feel free to tell me. I'll quit flying the day I quit learning!

[Will.iam]

15 hours ago, airmocha said:

For sake of understanding, if I didn't have an MB, would I need to open throttle to hold MAP constant while leaning? This whole thing sounds like a chicken/egg situation I find mind boggling. Blue screen of death here! Lol

Thanks to Brian Kendrick of Mooney Support on San Marcos, I can lean that far, though only that far, without what I perceive as "roughness" - but I admit my sense of such is highly subject to expectations.

 

My EGTs stay generally within 10 or 15 degrees of each other from near to beyond peak, and yes, my MAP does shift a little, but I always attributed the drop in % power to the fuel flow reduction alone, and never considered that my turbo is loading somewhat when I lean and rob it of all that energy at the turbine. That's where I get back to the chicken/egg and wonder where it ends?

If I start with 32/2500 or so in the climb (I actually see slightly higher TIT (yes at less fuel flow) at 30/2500, for reasons I don't yet fully understand), and throttle back to around 75% power (maybe, what, 26-28"/2300?), when I hit "LOP" on my JPI, I see peak TIT at very nearly the 1650 redline (yes, I do try to hurry through that setting), and end up at about 65% power. I don't recall how much my MAP drops, but i know it does some. 

I get enough "go fast on glass" at work,  so I'm an "efficiency" guy and "steam gauges" nostalgic, so I don't often run it that hard, however. I much more often throttle back further, to maybe just an inch or two over square, to about 55% power, and try to get to 50 LOP without roughness or a big EGT spread, and witness a peak TIT under 1600, and settle in to enjoy my beautiful old airplane at around 45% bhp.

I've only had it for about 200 hours over 5 years now, and just got the JPI/GAMIs to go LOP last year, but it seems OK with what I'm doing. No cylinder or turbo issues yet on a 15 years/500 hours old engine. Course I used to always run at least 50 ROP, and even cooler if I was pulling more than 65% bhp.

I'm just not a fan of marriage to fuel flows. Atmospheric and engine conditions just change too much too often for that. I think i understand the principles at work (turbo de-bootstrapping from leaning LOP excluded, lol) and pay very keen attention to TIT, hottest/leanest/richest cylinder, distances from their peak, and EGT spreads, and try to make/keep my hottest/leanest/richest cylinder safe,  with no outliers among the other 5 farther from danger, whether I'm operating LOP for efficiency at lower power, or ROP for speed at higher power.

 

Hope this makes sense - I'm not preaching...just disclosing. If I'm doing something bad or wrong, feel free to tell me. I'll quit flying the day I quit learning!

Mike busch in his turbo 310 doesn’t even know how far lop he leans to. He quickly pulls the mixture to roughness then enriches until smooth and that is his deepest lop fuel flow. Then he slowly enriches until he hits ether TIT or a cylinder temp reaches 380 and that is as rich as he will go on the lop side. His point is if you get into the red box area at high power settings it will drive your cht above 400 and at the ada engine test lab in OK they would operate an engibe full power at 50 ROP the absolute  worse place to run your engine but it doesn’t instantly start deteriorating in fact only once they saw the CHT go past 420 there would be detonation starting and damage. So if you keep your cht below 400 you should be safe from detonation and 380 or below will extend cylinder life. Bottom line don’t allow a cht to climb past 400 when operating at high power settings lop. And if you are below 65% power i doubt you would get above 400 cht at any mixture setting unless you had bad baffling cooling issues or was climbing to steeply and not enough cooling airflow. But if that is the case you probably are seeing that at full rich power takeoffs too. 

[Fix]

Question about some power settings and your thoughts about it.

If you fly at 65% or below it said that your fuel flow settings doesn't matter since you then are out side the red box.

So for 65% on -MB/SB Engine you have either:

65% LOP at 10.4g/h (you can have any preferred setting on MP/RPM, 27" / 2500) and then you are outside red box.
65% ROP, Key #50, ie: 25" / 2500 or 26" / 2400 and fuel flow at 12.6 g/h for 100 ROP.

So if I want to fly 65% ROP 25" / 2500 (Key: 50) can I set what ever fuel flow I want, long as TIT and CHT has good temps?
Like 11.5 g/h Peak TIT long as TIT is on safe temp like 1500-1600 and CHT below 380.




 

[Ragsf15e]

3 hours ago, Fix said:

Question about some power settings and your thoughts about it.

If you fly at 65% or below it said that your fuel flow settings doesn't matter since you then are out side the red box.

So for 65% on -MB/SB Engine you have either:

65% LOP at 10.4g/h (you can have any preferred setting on MP/RPM, 27" / 2500) and then you are outside red box.
65% ROP, Key #50, ie: 25" / 2500 or 26" / 2400 and fuel flow at 12.6 g/h for 100 ROP.

So if I want to fly 65% ROP 25" / 2500 (Key: 50) can I set what ever fuel flow I want, long as TIT and CHT has good temps?
Like 11.5 g/h Peak TIT long as TIT is on safe temp like 1500-1600 and CHT below 380.




 

Yes.  In fact, the poh gives you a 65% ff of 11.3gph for the sb.

I flew all 3 of these settings last week and put pictures in the link about Bravo operating costs.  The true airspeed was within 1 or 2 knots for those 3 settings which proves they are all about the same % power.

see the pictures on the last page near the bottom.  POH (peak egt), ROP, LOP.  All 65%, all ~same speed.

 

[Ragsf15e]

3 hours ago, Fix said:

Question about some power settings and your thoughts about it.

If you fly at 65% or below it said that your fuel flow settings doesn't matter since you then are out side the red box.

So for 65% on -MB/SB Engine you have either:

65% LOP at 10.4g/h (you can have any preferred setting on MP/RPM, 27" / 2500) and then you are outside red box.
65% ROP, Key #50, ie: 25" / 2500 or 26" / 2400 and fuel flow at 12.6 g/h for 100 ROP.

So if I want to fly 65% ROP 25" / 2500 (Key: 50) can I set what ever fuel flow I want, long as TIT and CHT has good temps?
Like 11.5 g/h Peak TIT long as TIT is on safe temp like 1500-1600 and CHT below 380.




 

One other note to add.  At 65% on my engine, there wasn’t a huge difference in temps, but it’s there.  LOP has the coolest cylinders, but slightly warmer tit.  ROP has warmer cylinders but cooler tit.  At 65%, none of the temps are even close to concerning.  
It does seem to take a well balanced fuel distribution and strong ignition system to get the tsio-360 running smoothly at LOP.  Mine has gami injectors, fine wire plugs and relatively new mags. At 65%, you can just be a little LOP and still be good (no red box), so that’s easier than trying to be more like 50 LOP at 75% power.

[Will.iam]

If 65% power then best power (fastest speed ) would be just rich of peak egt which would be the lowest margin from the red box. Peak would be slower and lop would be slower but cleanest running. Where LOP really shines is running power higher than 65% as historically before finding out it was balanced fuel flow, ROP was the only way to get there without shortening engine life. Now with balanced fuel flow you can enjoy the higher HP settings with a cleaner engine dictated only by how closely the injectors peak together and how much air you can squeeze through compared to fuel. If too far LOP the flame front is so slow that the exhaust valve will be opening while the mixture is still burning and thus your egt temps can exceed your tit temp limit. 

[Ragsf15e]

17 minutes ago, Will.iam said:

If 65% power then best power (fastest speed ) would be just rich of peak egt which would be the lowest margin from the red box. Peak would be slower and lop would be slower but cleanest running. Where LOP really shines is running power higher than 65% as historically before finding out it was balanced fuel flow, ROP was the only way to get there without shortening engine life. Now with balanced fuel flow you can enjoy the higher HP settings with a cleaner engine dictated only by how closely the injectors peak together and how much air you can squeeze through compared to fuel. If too far LOP the flame front is so slow that the exhaust valve will be opening while the mixture is still burning and thus your egt temps can exceed your tit temp limit. 

Possibly I’m being too specific here, but if you’re at 65% power, you will have the same airspeed no matter how you get there - ROP, LOP, or Peak.  If you’re in an NA airplane, you can only get MP up to a certain amount, then I agree with what you said - max power would be slightly ROP and yield the max airspeed, but in that case, ROP, LOP, or peak are different %power because you can’t get any more MP.  In our turbos, it’s possible to set 65% power with different combinations of ff, mp and rpm, but they all yield basically the same speed (possible exception for prop efficiency or some other minor difference).
 

If you are truly settling a % power, then airspeed will be the same ROP, LOP or whatever.  Look at the link I posted above and you’ll see 3 different settings LOP, ROP and peak for 65% all the same speed.

[Pinecone]

13 hours ago, Will.iam said:

If 65% power then best power (fastest speed ) would be just rich of peak egt which would be the lowest margin from the red box.

If you are at 65% power or less, there is no red box/red fin.

As was mentioned, 65% power is 65% power, no matter how you get there.