Lean Range Test Results

[alpinelakespilot2000]

I'd appreciate comments on a lean range test I did today. I have done it previously, but had not been able to do it WOT (as it should properly be done) until I had my prop repitched. It has been repitched and here are my results:

Test conditions:
WOT
8000' MSL
~9500' DA
-Made 4 runs, starting at full rich and taking about 6-8 minutes to slowly lean until all 4 cylinders peaked. Then went to full rich, allowed temps to stabilize, repeated the process 4 times.

Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F

The order in which each cylinder reached peak was always 2-1-4-3 and the standard deviation for each cylinder on all four runs above was within +/- 10F, so I'm pretty sure I got some accurate averages.

Average fuel flow delta from first peak to last peak was 1.14gph so, as expected, running LOP is tough, though I will experiment with some carb heat to see if that helps.

My main concern, especially given how high up I was, #2 seems to be running really lean (and that cylinder does generally run hot relative to the others) but anything else I can take from these numbers and/or should do or check for?

Thanks.

[Sig600]

What are the actual CHTs? That's the most important number for engine long term health. Carbureted engine is going to be tough to get an even spread.

[petehowell]

Steve,

Try a few levels of carb heat - I can really influence the mixture using varying levels of carb heat.

Also try the throttle a bit off the WOT stop.

Good luck - I can get my O-320 to run quite well LOP

[alpinelakespilot2000]

Thanks Pete. I m thinking the backing off the throttle a bit is key. I ran the same lean range test with the throttle backed off a bit and my lean ranges were exactly the opposite. The front two were the richest and the back two the leanest. Go figure. Actually I've learned to go back and forth between WOT and partial throttle in my climbs to deal with temps due to those front and back cylinders heating up and cooling opposite of each other. Not sure that this is the best way to handle it, but it sort of works.

My Dynon says i can get LOP, but just barely. Will start experimenting with some carb heat too.

[alpinelakespilot2000]

Originally Posted by Sig600

What are the actual CHTs? That's the most important number for engine long term health. Carbureted engine is going to be tough to get an even spread.

Usually I don't have trouble keeping cruise temps below 380 or so, but WOT climb, even at 500fpm, on a quick turn around can get #2 up into the 400s or low 410s pretty quickly. Otherwise I have to manage climb temps by alternating b/w WOT and partial throttle to keep climb temps below 400 in the summer. See post above responding to Pete.

[Sig600]

Mike Busch talks about using carb heat in his book, pick up a copy. Quick read lots of valuable info.

Some things I'd look at for climb temps...
Fuel flow at take off, are you getting enough fuel?
Baffle sealing, how good are they? Are you losing air anywhere?

DanH? He's pretty smart on this stuff.

[DanH]

Originally Posted by alpinelakespilot2000

Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F

I ran the same lean range test with the throttle backed off a bit and my lean ranges were exactly the opposite. The front two were the richest and the back two the leanest.

But was the delta between cyls as large? Some other cylinder only has a ~100 degree rich-to-peak with the new throttle position?

[RVbySDI]

Originally Posted by alpinelakespilot2000

I'd appreciate comments on a lean range test I did today. I have done it previously, but had not been able to do it WOT (as it should properly be done) until I had my prop repitched. It has been repitched and here are my results:

Test conditions:
WOT
8000' MSL
~9500' DA
-Made 4 runs, starting at full rich and taking about 6-8 minutes to slowly lean until all 4 cylinders peaked. Then went to full rich, allowed temps to stabilize, repeated the process 4 times.

Average EGT delta between full rich EGT and peak EGT:
Cylinder #1: 173.3F
Cylinder #2: 107.8F
Cylinder #3: 251.0F
Cylinder #4: 229.8F

The order in which each cylinder reached peak was always 2-1-4-3 and the standard deviation for each cylinder on all four runs above was within +/- 10F, so I'm pretty sure I got some accurate averages.

Average fuel flow delta from first peak to last peak was 1.14gph so, as expected, running LOP is tough, though I will experiment with some carb heat to see if that helps.

My main concern, especially given how high up I was, #2 seems to be running really lean (and that cylinder does generally run hot relative to the others) but anything else I can take from these numbers and/or should do or check for?

Thanks.

I will reinforce what Sig600 referred to when he asked about the CHT's. Information about EGT temps is valuable when initiating the LOP process and when you reach the LOP point but what really matters once you get to the point of running LOP are the CHT temps. CHT temps may or may not be in lock step together in a carbed engine but if they are well below 400 DEG during LOP operations your engine will be working fine. Pay attention to what the CHT readings are during LOP cruise settings and let us know what they show after your next test flight.

[alpinelakespilot2000]

Originally Posted by RVbySDI

I will reinforce what Sig600 referred to when he asked about the CHT's. Information about EGT temps is valuable when initiating the LOP process and when you reach the LOP point but what really matters once you get to the point of running LOP are the CHT temps. CHT temps may or may not be in lock step together in a carbed engine but if they are well below 400 DEG during LOP operations your engine will be working fine. Pay attention to what the CHT readings are during LOP cruise settings and let us know what they show after your next test flight.

Thanks for the input. In general, I pay almost no attention to EGTs operationally outside of LOP ops and for checking ignition health. Accordingly, I know CHT's matter much more than EGT but the CHT's are only secondary to what I'm interested in here and why I posted the initial question. I do, in fact, have some CHTs that run hotter than I like, but one of the reasons this may be the case is because I have one or more cylinder running really lean. That's why I ran Mike Busch's lean range test to see if a lean cylinder might be the cause of my high CHT. If I can fix that, then maybe the CHT issue will take care of itself. (???)

[alpinelakespilot2000]

Originally Posted by DanH

But was the delta between cyls as large? Some other cylinder only has a ~100 degree rich-to-peak with the new throttle position?

Thanks Dan. Yes, it was. The highlighted red below is the a test I ran last year before my prop got repitched allowing me to go WOT for the test. At that time, not realizing I was supposed to do the test WOT, I did it at partial power and ended up very concerned about the lean (and hot) #3 and #4 cylinders. Full thread here: http://www.vansairforce.com/communit...ght=lean+range
In the process of tracking down some high temps, I did a lean test through Mike Busch's Savvy Analysis Program. The lean range for my four cylinders are:
1-205F
2-222F
3-68F
4-62F
Test was conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.
I still get these same numbers, more or less now when I run the test at less than full throttle.

I may be wrong, but this wide disparity between what the lean ranges are from WOT (#1 and #2 very lean) to what they are at reduced power setting (#3 and #4 lean) leads me to believe that at least some of my CHT problem is a fuel distribution one rather than primarily one of my baffles (admittedly probably not perfect and that I continue to work on) or a possible induction leak which I've tried very hard, with no avail, to detect. Is there any possible truth to this?