Scott, thanks for all the info you post. It’s always interesting to get opinions on leaning. I currently run my TR182 (O-540 L3C5D) ~125-150 ROP for most ops after several mechanics strongly recommended against running at peak TIT. I upload all of my engine data as well. However, ROP ops will increase valve buildup and sticking…
If I run peak TIT I’m usually at 65% power (23/2100). At this setting peak TIT is around 1500 for me and FF is just under 11. Engine temps seem fine at this setting…not exceeding 400.
I’m curious what others are doing? Maybe I should be running peak TIT instead of ROP?
Hi Nad, when you are following the advice of a person, mechanic or otherwise, it is good to ask why should you be putting trust into what they are saying?
Why are they saying to run that way, do they have an explaination?
Do they know there is no maximum TIT or EGT engine or airframe limit?
Were they a Cessna or Lycoming engineer on the original flight test certification team?
Do they have access to TR fleet turbo use and TBO data since 1978?
Do they operate a TR? For how long? Have they run one to TBO and beyond?
Do they maintain multiple TR’s for long enough to have the turbo’s and engines reach TBO?
What Cessna, Lycoming, and owner groups SAE or peer reviewed engineering studies are they getting their data from?
Does their “advice” conform to the POH and OEM operator manuals?
I'm curious, have they ever provided you with a reason to not run at max TIT?
Scott, a good post but a couple of points to mention for turbo owners.
When I got the TR I was starved for information on proper engine ops, Paul New’s class was most helpful, I highly recommend it, it is worth every penny. But good engineering information for the user is really lacking. Even more so when I converted to Electroair electronic ignition last year. You are your own test pilot.
Paul's classes can be purchased online and then you have access and can rewatch anytime.
In this document the leaning for turbos only applies to Lycoming turbo motors. Ours are naturally aspirated engines with Cessna designed and installed turbo systems which are accessories and Cessna part numbers. Lycoming has nothing to do with them, thus the guidance, while related does not “legally” apply.
Cessna applied NO TIT limits in the POH or maintenance manual. Of course there are also no EGT limits. The aircraft was certified with a single probe in the LH manifold to capture peak EGT with no temperature indication and no ability to measure TIT.
I have summarized pertinent info from the POH, maintenance and Lycoming operator manual. So maybe it will help others in finding where the limited info is located. If anyone has anything else they have found, please post.
Lycoming's bulletin recommendations do not match Cessna's POH guidance.
Leaning instructions in POH, page 4-1, Cruise, #3 “Mixture – LEAN”.
In the POH Amplified Procedures:
Cruise power is to be 55-75%.
Figure 4-4 recommended leaning (for best power) is 50 F ROP. Best economy is peak EGT.
Mixture is to be leaned further in descent to “smooth operation”.
It also states that, “roughness may occur before peak EGT, to keep leaning for peak and enrich as desired for smooth operation”.
In the POH Performance Section:
“For best fuel economy, operate at the leanest mixture that results in smooth engine operation or peak EGT.”
In both cases above this is LOP operation for best economy. This is a direct contradiction to Lycoming’s bulletin. The bulletin does differ to the POH, which in our case takes precedence.
Some other important points:
Max CHT, 500 (Lycoming tests to just a wee bit above this).
Recommended max CHT for long life is 2/3rd the green arc which is 200-500, thus 400 F.
Paul New’s legacy 182 class has additional recommendations which are quite insightful.
Some interesting info from the Lycoming “-L”, naturally aspirated manual, 4th Edition, 2006:
For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operation and below 400°F (205°C) for economy cruise power.
LEANING TO EXHAUST GAS TEMPERATURE GAGE.
1. Normally aspirated engines with fuel injectors or carburetors.
(a) Maximum Power Cruise (approximately 75% power) – Never lean beyond 150° F on rich side of peak EGT unless aircraft operator’s manual shows otherwise. Monitor cylinder head temperatures.
(b) Best Economy Cruise (approximately 75% power and below) – Operate at peak EGT.
LEANING WITH MANUAL MIXTURE CONTROL (Without flowmeter or EGT gage).
1. Carbureted Engines.
(a) Slowly move mixture control from “Full Rich” position toward lean position.
(b) Continue leaning until engine roughness is noted.
(c) Enrich until engine runs smoothly and power is regained.
This is LOP on carbureted engines. It should be noted that Fig 3-1, page 3-6 shows Best Economy is lean of peak EGT at 5-10 deg LOP.
Page 3-11
*** - Model O-540-L Engines – Manual leaning at best economy is permitted at cruise conditions up to 75% power resulting in a BSFC of .430 lbs./BHP./hr. Minimum allowable BSFC at take-off and climb is .550 lbs./BHP./hr.
This is a good fuel flow check for take off and climb, 0.55 lbs. translates to approximately 21.6 gph at 235 hp.
Thanks for all of this info. I did take Paul New's class when I first acquired the airplane, and I agree there was alot of good info. I became conflicted though after I uploaded all of my engine data to the Savvy website and the engine analysis team recommended I operate ROP. From the best of my recollection the data showed I was able to get 2 cylinders slightly LOP, 2 at peak and 2 slightly ROP when I did the GAMI lean test. The concern was the 2 cylinders that might be running in the "detonation zone".
It is further obscured by the lack of relevant data in the POH, which as you pointed out recommends 50 degrees ROP in cruise for best power. From my understanding 50 ROP is the worst possible place to be operating as it is the maximum detonation zone. Then the Lycoming manual which recommend operating at peak TIT....so much conflicting info...
With that said the CPA course says basically lean to wherever you want if you are 65% power. So I probably should be running leaner (to the onset of roughness and then just slightly enrichen) to prevent valve sticking and save ROP ops for 70-75% power settings. Thoughts?
Here is an example flight where I manually leaned to the onset of roughness. I'm always open to an opportunity to learn, and I appreciate the discussion!
Nad, I agree it is sad that data/info is so anemic. But that was the way it was 45 years ago.
POH numbers came from test pilots on brand new aircraft. Endurance is likely from LOP best case. Speed, ROP leaned to best speed.
I’m not advocating lean of peak on carbureted engines, even if our fore fathers did it all the time.
I’m just pointing out the conflict with the certificated data and Lycoming’s bulletin. The same has been pointed out in Piper documents.
On your GAMI test, you didn’t mention what % power setting you were at? The “detonation zone” supposedly doesn’t matter if you are 65% or lower. So why did Mr. Bush think your test point produced risk? At any point the cylinders will have different A/F ratios.
Also, as you pointed out from more recent publications and a lot of GAMI work any setting when less than 65% power is ok. Our POH manual points out a specific, 150 deg point at MAX power cruise, 75%. I haven’t checked but running 50 ROP vs. 150 at any power setting is likely about a ½ gph. Thus, it costs you $5 extra bucks on a 2-hour flight.
Who cares about that? Focus should be on CHT’s.
Generally, I always run around 68-70% power in cruise, managing CHT’s to 390 in the warm months trying to lean for best speed. I bought it to go faster than my Taylorcrafts, fuel burn $’s don’t matter. As I continue to test, I’m trying to find a sweet spot, high MP and continuing to lower RPM which the lower rpm will drop fuel flow way more than a few degrees of EGT and have less wear on the engine while trying to maintain best speed.
Now I suspect that with the Electroair ignition you can run our turbo motors LOP. The difference when leaning to “first roughness” from the mags vs. electronic is astounding. But that is another topic subject. My engine is very different on electronic ignition, CHT’s are higher and EGT’s lower.
This thread points out enough conflicting info for further review. Let me contact our Lycoming Tech Rep to see about scheduling a Zoom call.
I'm not convinced Lycoming's ROP only recommendations make sense including their rationale for it. The data matters!
I've heard from many operators for many years running LOP(including TCM users) that below 65% power no harm can result. Another obvious limitation here is our 1970's era induction system delivering a carbureted fuel air mixture is less than ideal for LOP ops.
Has anyone tried partial carb heat and compared the data?
Great discussion here.
I’d be very interested in a webinar with a Lycoming rep on leaning specific to our engine. Basically everyone I have talked to has had different advice, and I am probably routinely running richer than I should right now. So, I think that would be great to hear directly from the source. Also I’ve done GAMI tests with and without carb heat, and have the data. For me it didn’t make an appreciable difference. I can share the data when I get back to my computer, but am traveling right now. Thanks again to everyone that replied!
mrbTR182 wrote: Thu Jun 05, 2025 3:10 pm
Nad, I agree it is sad that data/info is so anemic. But that was the way it was 45 years ago.
POH numbers came from test pilots on brand new aircraft. Endurance is likely from LOP best case. Speed, ROP leaned to best speed.
I’m not advocating lean of peak on carbureted engines, even if our fore fathers did it all the time.
I’m just pointing out the conflict with the certificated data and Lycoming’s bulletin. The same has been pointed out in Piper documents.
On your GAMI test, you didn’t mention what % power setting you were at? The “detonation zone” supposedly doesn’t matter if you are 65% or lower. So why did Mr. Bush think your test point produced risk? At any point the cylinders will have different A/F ratios.
Also, as you pointed out from more recent publications and a lot of GAMI work any setting when less than 65% power is ok. Our POH manual points out a specific, 150 deg point at MAX power cruise, 75%. I haven’t checked but running 50 ROP vs. 150 at any power setting is likely about a ½ gph. Thus, it costs you $5 extra bucks on a 2-hour flight.
Who cares about that? Focus should be on CHT’s.
Generally, I always run around 68-70% power in cruise, managing CHT’s to 390 in the warm months trying to lean for best speed. I bought it to go faster than my Taylorcrafts, fuel burn $’s don’t matter. As I continue to test, I’m trying to find a sweet spot, high MP and continuing to lower RPM which the lower rpm will drop fuel flow way more than a few degrees of EGT and have less wear on the engine while trying to maintain best speed.
Now I suspect that with the Electroair ignition you can run our turbo motors LOP. The difference when leaning to “first roughness” from the mags vs. electronic is astounding. But that is another topic subject. My engine is very different on electronic ignition, CHT’s are higher and EGT’s lower.
Thanks for the reply. The GAMI tests I have done have all been at 60-65% power. So yes I should be able to lean to whatever setting I want hypothetically. But I was just looking for some specific recommendations based on the data I was pulling for my airplane. Even different people at Savvy seemed to have different opinions though. The first guy I talked to about it recommended leaning to the onset of roughness and then enrichening a few turns, which is generally discouraged in most of Savvy's published material. The next guy recommended running 100-150 ROP TIT. No one gave a concrete answer of why they didn't recommend running at peak TIT or as lean as possible though.
I pretty much agree with you on all points, and do focus on CHT's (keeping under 400). However, CHT's can vary significantly depending on cowl flaps, OAT, and headwind vs. Tailwind. My hypothetical concern is not about $$ spent on extra fuel running 100-150 degrees ROP, but trying to limit the chance of sticking valves from lead oxy-bromide buildup.
Mostly I'm curious to see if there is any general consensus out there from anyone with more expertise than me (that is data driven), because the recommendations that I've run across seems so opinion based. So I would welcome some input from Lycoming. Thanks again.
