Wondering if I should be leaning more aggressively

[M20 Ogler]

I’m burning 13 gph. M20C Lycoming O-360 Power flow exhaust. Most of my flying lately has been between 3000’ and 5000’ at 24” and 2400 rpm. I’ve just been selecting the cylinder with the highest EGT and leaning it to 100 ROP. What fuel burn are other C operators getting? 

[Rwsavory]

We consistently average 10 gallons per hour over the course of a trip with wide open throttle, 2400 RPM, usually between 7000 and 9000 MSL. I lean until there’s a bit of roughness and then enrichen slightly from there.

[Boilermonkey]

The M20C I had for years burned 10gph consistently.  EGTs were typically in the 1300s.  

Are you getting your 13 gph number from a gauge?  When was the last time it was calibrated?  Have you correlated with how much you are putting in the tanks?   

If you are indeed burning 13gph, at 100deg ROP, then something should be investigated.

[BobbyH]

13 minutes ago, Rwsavory said:

We consistently average 10 gallons per hour over the course of a trip with wide open throttle, 2400 RPM, usually between 7000 and 9000 MSL. I lean until there’s a bit of roughness and then enrichen slightly from there.

I run around the same parameters and average on the whole flight around 9 gpm.  One difference is the fuel injection, other than that the M20E is pretty similar to the M20C.

[M20 Ogler]

I get 13 gph based on flight time and how much fuel it takes to top off the tanks. I flew 2 hours (tach time) and to fill back up took 25.8 gallons so 12.9 gallons per hour  actually 

[Boilermonkey]

I would say that is too high of a fuel burn.  Others might be able to speculate better on cause.

[Fly Boomer]

36 minutes ago, M20 Ogler said:

2 hours (tach time) and to fill back up took 25.8 gallons so 12.9 gallons per hour  actually 

Tach time may not be the best way to calculate GPH.  What you really want to know is how much you are burning at cruise.

[TheAv8r]

Yeah, I've never cruised at that gph in a C model.

Few things come to mind:

• Very uneven fuel distribution, the hottest cylinder is getting a lot less fuel than the others, so by enrichening it to 100deg ROP you're giving the other 3 cylinders way more fuel
• What are your CHTs at that rate?
• Have you checked for any signs of a fuel leak? Blue staining underneath the wing, blue staining on the belly? 
• Goes hand in hand with #2, but how old are your EGT probes? Wonder if they're giving you bad info...

[hammdo]

I do 23 squared below 5k and I lean to the highest CHT (~395 or less) - yes CHT since fuel distribution is not linear.

I get a fuel burn around 9 GPH or less actual time of start up to shut down.

- Don

[M20 Ogler]

No leaks. My only cht is the factory gauge so I just check it’s in the green. My egt probes are nearly new. 
 

I suspect I’m not leaning aggressively enough. Maybe I’ll try leaning the coolest or 2nd coolest egt to 100 ROP instead of the hottest one 

Edited June 24, 2022 by M20 Ogler

[Hank]

2 hours ago, M20 Ogler said:

I’m burning 13 gph. M20C Lycoming O-360 Power flow exhaust. Most of my flying lately has been between 3000’ and 5000’ at 24” and 2400 rpm. I’ve just been selecting the cylinder with the highest EGT and leaning it to 100 ROP. What fuel burn are other C operators getting? 

Too high power settings! For our O-360, the key number is either 46 or 47, I forget--I use 46.

MP + RPM = Key Number

I cruise at 5-7K using 22" / 2400 = 46, around 9 gph. At 8-10 k, whatever MP I van get, backed off just enough to make the MP needle wiggle and 2500. When refilling tanks, this is often less than 9 gph.

[Shadrach]

Why are you using the highest EGT? That does not necessarily mean the leanest. Use the cylinder that peaks first for ROP engine settings. That may or may not be the hottest EGT.

[carusoam]

Alert!

It has been a decade+ since I flew the M20C…

We cruised near 10k’ wide open throttle… probably 2500rpm or less…

With little instrumentation… averaging near 10gph over 1k hours….

T/O FF will be closer 2X cruise FF….

So…. Following Hank’s numbers above…

Get a grip on MP, and rpm first… then work on leaning…

 

Hank has written a ton about how to lean his O360…. It has normal carb related quirks to be aware of…
 

When it comes to leaning… check your post…

Did you really mean hottest EGT?

This will be important for how much you understand about EGTs…

What %bhp do you get at 24/24? 70+ ?

Most people want to cruise using 65%bhp or less before running leaning experiments….

Find a power chart for your engine…  MP, rpm, and FF are well known numbers and shouldn’t be hard to find…

leaning aggressively above 65%bhp is known to be problematic in some cases… read up on the red fin or other topics of things to avoid while leaning… 

Best regards,

-a-

 

[Ragsf15e]

As @Shadrachsaid, the “hottest” egt isn’t really a thing.  The egt number values don’t matter.  Use the egt trends to find your leanest cylinder.  Set 100rop from that. So no matter the value, first egt to peak is the leanest.  Use that one even if another egt is “hotter.”

Also, a lot of people will cruise below 75% power which will help.  Not a concern up higher when thin air forces that but down low might require a small power reduction.  Either from poh guide or key numbers as @Hank said.

[47U]

On 6/24/2022 at 7:51 AM, M20 Ogler said:

I’m burning 13 gph. M20C Lycoming O-360 Power flow exhaust. Most of my flying lately has been between 3000’ and 5000’ at 24” and 2400 rpm. 

1 hour ago, Ragsf15e said:

Either from poh guide or key numbers as @Hank said.

The ‘65 POH, one year before your ‘66, says you’re burning too much fuel at 24 squared, 3-5k feet MSL.  Although, the PFE will burn a little higher gph.  

Then, the ‘77 POH (with presumably better data?) says you’re not burning enough fuel.  With the admonition to not lean below 75% power.  

And the 5,000’ chart.

I’m flying at fuel flows inline with what Hank says.  I think the ‘77 POH is overly conservative. 

[Ragsf15e]

57 minutes ago, 47U said:

The ‘65 POH, one year before your ‘66, says you’re burning too much fuel at 24 squared, 3-5k feet MSL.  Although, the PFE will burn a little higher gph.  

Then, the ‘77 POH (with presumably better data?) says you’re not burning enough fuel.  With the admonition to not lean below 75% power.  

And the 5,000’ chart.

I’m flying at fuel flows inline with what Hank says.  I think the ‘77 POH is overly conservative. 

You can find a lycoming recommendation “for maximum engine longevity” to cruise below 75% power.  Which also would allow leaning per the poh, and the key numbers work there as well.  It all kind of comes together at 75% power or less.  However, if you’re racing and don’t care about ff or longevity, perhaps greater than 75% power becomes a better cruise option. 

[A64Pilot]

He’s down low, running pretty hard, best to be a little rich to protect the motor

If you want to save fuel, try 22 squared and run at peak, or as was said pull until she stumbles, then slowly increase until smooth, that will put you pretty close to peak. It’s the time honored way to lean a carb motor, and it works. But only do that at lower power settings, less than 75% power. Lycoming has said in print that a motor will last longer if run at 65% or less power, so you save fuel and extend the life of your motor.

Life is still good at lower power settings, sure a little slower, but not as much as you may think, and you can save a LOT  of fuel. I burn half your fuel and cruise 120-125 kts, but I’m FI and can go LOP so you can’t get quite that good, but big fuel savings can be had at peak and lower power.

If your flying far enough to justify higher altitudes, higher will let you go faster on less fuel.

[DXB]

On 6/24/2022 at 10:51 AM, M20 Ogler said:

I’m burning 13 gph. M20C Lycoming O-360 Power flow exhaust. Most of my flying lately has been between 3000’ and 5000’ at 24” and 2400 rpm. I’ve just been selecting the cylinder with the highest EGT and leaning it to 100 ROP. What fuel burn are other C operators getting? 

My O-360 in the C model got a HUGE power increase from this exhaust. Along with that power gain comes increased fuel consumption. I'm not at all surprised you get 13gph at 100 ROP, 24-squared. Leaning at all at that high power setting may be somewhat abusive for the engine (power is higher than the POH charts predict for that MP/RPM and mixture because of the exhaust). It should also haul ass at that setting (well over 150 kt - maybe even close to 160kt at 5-6k ft).  By contrast, at 23-squared, burning ~8gph with one or two cylinders running LOP is completely feasible in my experience and still gives good performance in the low 140's for knots TAS.