GAMI Lean Test

[azure]

I've been interested for a while in finding out if I can run LOP with my current (non-GAMI) injectors so yesterday I printed out the GAMI data form, took my Cardinal up to 7800 MSL (pressure altitude 7500), chose a 65% (by the POH) power setting, and tried to run the longhand form of the lean test.

I failed. The main problem was that I couldn't figure out how to get my EDM-700 to display the cylinder I wanted it to display in Lean Find mode. It turns out it can't do that, in LF mode it only displays the warmest cylinder. In Manual Mode the digital EGT display only has 10F resolution, which isn't good enough for the test. So instead I tried reverting to the shorthand form of the test after finding the first cylinder to peak (#3). The problem is that #4 peaked next, at a lower temp than #3 so it never displayed in LF mode. In fact I wasn't able to record its peak temp as the display just flashed "PEAK EGT" while switching to #4, without telling me the actual EGT value. Then #2 started to climb up to about 1470 -- and went up and down a few times as I continued to lean very slowly. I then switched to #1 in manual mode and found that it was already LOP -- LF mode had never informed me of that fact. So basically LF mode is useless for the lean test.

Later at night I learned (by RTFing) that it's possible to change the EGT resolution. What I'm wondering now is whether I should just do it again (quite time consuming, I was up there fiddling around for about 45 minutes) or whether I already have enough information to know that I can't run LOP. Here's the relevant data on each cylinder:

cylinder.......PEAK EGT(F)..........FF(gph)
#3.................1450.................8.7, 8.5 (did this twice)
#4.................unk...................8.0
#1...............~1440.................unk, but <8.5
#2.................1470-1480.........7.8

So it seems my total FF spread is 0.7-0.9 gph which is well above the GAMI ideal of 0.5. Also, it seems I really can't run #2 LOP at all as the engine starts running noticeably rough in that regime.

However I never saw alarmingly high CHTs, in fact during the test they were always lower than they were during climbout (315 or less). LOP they were back down in the high 200s -- and even at peak EGT, #2's CHT was cooler than #3 at peak EGT (302). I typically only see CHTs above 350 during climbout in summer heat. According to Mike Busch, CHT is the best proxy for ICP... not sure how to apply that concept to my (apparently) unusually cool-running engine.

 

[Lance F]

What are you using to measure fuel flow? I think Cardinals have about the same engine as the Mooney. Most IO360A3B6Ds like mine run just fine LOP with the stock Lycoming injectors. You just don't need GAMIs. My GAMI test with the stock injectors showed virtually zero difference and runs great LOP. I am suspicious of your numbers.

 

[azure]

The engine is an IO360-A1B6 (non D) and the FF meter is the stock Cessna analog gauge. Which numbers are you suspicious of? I wouldn't trust the absolute FF values, but the only relevant number is the spread, and I don't see any reason not to trust that.

 

[gismo]

I failed. The main problem was that I couldn't figure out how to get my EDM-700 to display the cylinder I wanted it to display in Lean Find mode. It turns out it can't do that, in LF mode it only displays the warmest cylinder. In Manual Mode the digital EGT display only has 10F resolution, which isn't good enough for the test. So instead I tried reverting to the shorthand form of the test after finding the first cylinder to peak (#3). The problem is that #4 peaked next, at a lower temp than #3 so it never displayed in LF mode. In fact I wasn't able to record its peak temp as the display just flashed "PEAK EGT" while switching to #4, without telling me the actual EGT value. Then #2 started to climb up to about 1470 -- and went up and down a few times as I continued to lean very slowly. I then switched to #1 in manual mode and found that it was already LOP -- LF mode had never informed me of that fact. So basically LF mode is useless for the lean test.

Later at night I learned (by RTFing) that it's possible to change the EGT resolution. What I'm wondering now is whether I should just do it again (quite time consuming, I was up there fiddling around for about 45 minutes) or whether I already have enough information to know that I can't run LOP. Here's the relevant data on each cylinder:

cylinder.......PEAK EGT(F)..........FF(gph)
#3.................1450.................8.7, 8.5 (did this twice)
#4.................unk...................8.0
#1...............~1440.................unk, but <8.5
#2.................1470-1480.........7.8

So it seems my total FF spread is 0.7-0.9 gph which is well above the GAMI ideal of 0.5. Also, it seems I really can't run #2 LOP at all as the engine starts running noticeably rough in that regime.

First switch your EGT resolution to 1°F and run the test again. I recommend that you use an altitude/power setting that has the throttle wide open and the RPM set at something you normally use in cruise (or slightly higher, more on that in a minute). It also helps if you "Normalize the display when the first cylinder peaks, that way you can readily observe the order in which the remaining cylinders peak. GAMI says to perform the test with one sweep of FF, either from the rich or lean side of all peaks. My preference is to do it both ways (going from rich to lean and vice versa) and average the results. Another option which takes much longer IME is to tweak the mixture back and forth until you find the exact peak EGT and associated FF for each cylinder (takes 3 times as long on my pair of 6 cylinder engines as it would on your one 4 cylinder so maybe it won't take long enough to be a concern). FWIW, a scale (slope) error on your FF gauge will affect the results but it would take a rather large scale error to matter.

The absolute best way to accomplish this is to utilize a recording engine monitor with EGT and FF. For that you set the sample rate as high as you can and run the mixture from ROP to LOP and back a couple times, slowly enough that you get at least 5 samples for every .1 gph change in FF. Then you can curve fit the peaks and get a very accurate FF for each.
FF can be added to your EDM-700 for this purpose but that costs about as much as a set of GAMI injectors (nice to have though). You can accomplish something almost as good if you can move your mixture control smoothly and slowly at a specific number of seconds per GPH while recording the EGTs on the JPI. Knowing the FF change per second lets you generate the FF data after the fact in a spreadsheet with only an (unimportant) offset error.

The egView/egTrends software will actually do the curve fitting for you if you have the data. http://www.egtrends.com/

However I never saw alarmingly high CHTs, in fact during the test they were always lower than they were during climbout (315 or less). LOP they were back down in the high 200s -- and even at peak EGT, #2's CHT was cooler than #3 at peak EGT (302). I typically only see CHTs above 350 during climbout in summer heat. According to Mike Busch, CHT is the best proxy for ICP... not sure how to apply that concept to my (apparently) unusually cool-running engine.

The folks at GAMI and APS object to Mike Busch's simplification that suggests that CHT is sufficient for determining safe peak ICPs. They do agree that high peak ICP correlates with raised CHT but they also believe that there are too many other factors that affect CHT for that to be used in this manner and I agree. But I wouldn't be concerned about ICP in your engine if you start with a ROP mixture that the POH or engine manual says should put the output at 65%. When you lean the mixture to peak EGT the power drops a few percent putting you safely outside the "red box" where ICPs can be a problem and in any case operating with slightly elevated peak ICP for a minute or two won't cause any damage.

BTW, there is a dirt simple way to determine if your engine will run LOP. Just set the mixture for something in the 80-100°F ROP area, let the airspeed stabilize, lean the mixture until the engine begins to get rough, and then enrichen until it just becomes acceptably smooth. Let the airspeed stabilize and if it's dropped 4% or more you're good to go. This works because going from best power (80-100 ROP) to sufficiently LOP for safe operation causes about a 12% drop in power and at cruising speeds (where parasite drag dominates) power is proportional to the cube of airspeed.

 

[azure]

Lance, thanks for the detailed reply. I'll try this again when I can with the EGT resolution in the 1F mode -- but my plane is going down for annual this week and I need to have some stray oil on the bottom of the oilpan checked out before I fly it again anyway. I do have a couple of questions though, if you don't mind explaining a bit further...

First switch your EGT resolution to 1°F and run the test again. I recommend that you use an altitude/power setting that has the throttle wide open and the RPM set at something you normally use in cruise (or slightly higher, more on that in a minute). It also helps if you "Normalize the display when the first cylinder peaks, that way you can readily observe the order in which the remaining cylinders peak.

I'm not sure I see the advantage of Normalize view here... ? Whenever you activate it all it does is put all the columns at the same level. It doesn't change the bar graph resolution, which I believe is always 25F -- once the first peaks, the others are within 50F anyway, so at most they will change by two squares before peaking, and some peak lower anyway. I also think (not sure) that Normalize gets rid of the missing segment display for CHT, which is something I like to have in sight when I'm playing around in this regime.

GAMI says to perform the test with one sweep of FF, either from the rich or lean side of all peaks. My preference is to do it both ways (going from rich to lean and vice versa) and average the results. Another option which takes much longer IME is to tweak the mixture back and forth until you find the exact peak EGT and associated FF for each cylinder (takes 3 times as long on my pair of 6 cylinder engines as it would on your one 4 cylinder so maybe it won't take long enough to be a concern).

Yes, tweaking back and forth is what I was trying to do. Kind of hopeless without 1F resolution though, given that you have no control over which cylinder LF mode displays.

FF can be added to your EDM-700 for this purpose but that costs about as much as a set of GAMI injectors (nice to have though). You can accomplish something almost as good if you can move your mixture control smoothly and slowly at a specific number of seconds per GPH while recording the EGTs on the JPI. Knowing the FF change per second lets you generate the FF data after the fact in a spreadsheet with only an (unimportant) offset error.

I can always dream! I've considered adding the FF option but as you say, it's expensive. The only way to download data from my unit is via a serial connection, and I no longer have a computer that has one...

The folks at GAMI and APS object to Mike Busch's simplification that suggests that CHT is sufficient for determining safe peak ICPs. They do agree that high peak ICP correlates with raised CHT but they also believe that there are too many other factors that affect CHT for that to be used in this manner and I agree. But I wouldn't be concerned about ICP in your engine if you start with a ROP mixture that the POH or engine manual says should put the output at 65%. When you lean the mixture to peak EGT the power drops a few percent putting you safely outside the "red box" where ICPs can be a problem and in any case operating with slightly elevated peak ICP for a minute or two won't cause any damage.

I wouldn't have thought I could damage anything at 65% or below... but that brings me to another question. I spent a good half hour at altitude trying several times to locate the peak in my #2 cylinder. The #2 EGT was well up in the 1470-1480F range and at the lean end of this, the engine was definitely not happy. On my next takeoff after the lean test (after about an hour cooldown, WOT, max RPM, and full rich), the #2 EGT started to rise well above the rest. Before I could manually switch to the #2 display to watch it I had a traffic alert (a NORDO entering base for the opposite direction runway), and after I had taken evasive action the cylinders were even again (from experience, by 200 AGL or so they should all be as high as they're going to get, so I suspect #2 came down). I did two takeoffs after that and both times all cylinders behaved normally as far as I could tell. A bit of sediment in the fuel? I really hope I didn't do any damage.

BTW, there is a dirt simple way to determine if your engine will run LOP. Just set the mixture for something in the 80-100°F ROP area, let the airspeed stabilize, lean the mixture until the engine begins to get rough, and then enrichen until it just becomes acceptably smooth. Let the airspeed stabilize and if it's dropped 4% or more you're good to go. This works because going from best power (80-100 ROP) to sufficiently LOP for safe operation causes about a 12% drop in power and at cruising speeds (where parasite drag dominates) power is proportional to the cube of airspeed.

Based on that criterion I should be able to run LOP. My airspeed drop going from ROP to the point where the engine just starts to roughen a little is about 5 kts, which at 120 kts is >4%. But is that really a reliable gauge? Isn't it possible to have all but one cylinder sufficiently fuel-starved to drop the airspeed by 4%, but still have the one cylinder in the red box?

 

[gismo]

I'm not sure I see the advantage of Normalize view here... ? Whenever you activate it all it does is put all the columns at the same level. It doesn't change the bar graph resolution, which I believe is always 25F -- once the first peaks, the others are within 50F anyway, so at most they will change by two squares before peaking, and some peak lower anyway. I also think (not sure) that Normalize gets rid of the missing segment display for CHT, which is something I like to have in sight when I'm playing around in this regime.

Actually Normalize does improve the display resolution from 25°F to 10° and since the absolute EGTs are irrelevant, the higher resolution plus the more closely aligned bars makes it easier to see when the direction of the temp reading reverses. Using Normalize is not mandatory but I find it helpful, especially if you manage to activate the function when the first EGT peaks.

As to the CHT display, it's still there in normalize mode (the CHTs are not normalized). And if you manage to get an EGT bar to drop below the lower limit, the CHT temp will be shown as a single illuminated dash (reverse video).

Yes, tweaking back and forth is what I was trying to do. Kind of hopeless without 1F resolution though, given that you have no control over which cylinder LF mode displays.

Even with 1° numeric resolution it's not easy as the EGTs tend to "wander" at least a few degrees when the mixture is constant. That's why the recorded EGT analysis with a constantly changing FF rate is more accurate.

I can always dream! I've considered adding the FF option but as you say, it's expensive. The only way to download data from my unit is via a serial connection, and I no longer have a computer that has one...

There are a couple options to resolve the download issue and I strongly recommend you adopt one of them. The least expensive is a USB to RS232 adapter. JPI sells the Keyspan 19HS adapter they recommend for $50 but I've seen (and purchased) them for about half of that
(http://tinyurl.com/keyspan-HS19). For about $200 you can add a USB port/box to the JPI and with that all you need for downloads is a flashdrive.

I wouldn't have thought I could damage anything at 65% or below... but that brings me to another question. I spent a good half hour at altitude trying several times to locate the peak in my #2 cylinder. The #2 EGT was well up in the 1470-1480F range and at the lean end of this, the engine was definitely not happy. On my next takeoff after the lean test (after about an hour cooldown, WOT, max RPM, and full rich), the #2 EGT started to rise well above the rest. Before I could manually switch to the #2 display to watch it I had a traffic alert (a NORDO entering base for the opposite direction runway), and after I had taken evasive action the cylinders were even again (from experience, by 200 AGL or so they should all be as high as they're going to get, so I suspect #2 came down). I did two takeoffs after that and both times all cylinders behaved normally as far as I could tell. A bit of sediment in the fuel? I really hope I didn't do any damage.

Hard to guess the cause but 1500F EGTs are no cause for alarm. Depending on probe location, 1600F is quite plausible and shouldn't raise any concerns. OTOH if you see a CHT climbing rapidly it's time to do something (increase FF and/or decrease MP).

Based on that criterion I should be able to run LOP. My airspeed drop going from ROP to the point where the engine just starts to roughen a little is about 5 kts, which at 120 kts is >4%. But is that really a reliable gauge? Isn't it possible to have all but one cylinder sufficiently fuel-starved to drop the airspeed by 4%, but still have the one cylinder in the red box?

The expectation is that if one cylinder is running significantly richer than the rest you'd feel the roughness created by that cylinder making way more power than the others. In addition, the "experts" have concluded that unless someone "cleaned" one of your injectors with a stiff wire or otherwise enlarged the opening, it's unlikely you'd ever see one running significantly rich when the others were nearly equal but leaner. I'm not 100% convinced of that but so far haven't experienced anything to contradict it. And if you did have that happen you'd likely see a very noticeable CHT increase on that cylinder compared to the rest which should be cause for further investigation.

But since you do have an analyzer I think it's a good idea to periodically examine the relative cylinder mixtures with that tool.

 

[spinfire]

What RPM were you running WOT at 7500? I haven't done a serious test like this in my Cardinal. I have tried a "big mixture pull" at 2400 RPM and both 7500 and 8500 feet, right through peak as shown on the GEM bargraph (I have an early model GEM). It doesn't seem to run as smooth as it does at peak or ROP at this altitude, but maybe I am over thinking this slight roughness. The engine runs so much smoother than the flight school 172s I was flying before that maybe I am biased. In any case, I have generally not continued to operate at that mixture, instead enrichening until it is smooth "by ear". And, of course, this is at low power levels, 2300-2400 RPM at 7500 feet or more WOT. IIRC Lycoming says operation at peak is best economy at these power levels.

I'd also note that as I understand it the fuel "flow" gauge is really a fuel pressure gauge calibrated in flow. It might not even be linear, especially at lower fuel flows. I'd really like to add some real fuel flow instrumentation... someday.

 

[azure]

Actually Normalize does improve the display resolution from 25°F to 10° and since the absolute EGTs are irrelevant, the higher resolution plus the more closely aligned bars makes it easier to see when the direction of the temp reading reverses. Using Normalize is not mandatory but I find it helpful, especially if you manage to activate the function when the first EGT peaks.

As to the CHT display, it's still there in normalize mode (the CHTs are not normalized). And if you manage to get an EGT bar to drop below the lower limit, the CHT temp will be shown as a single illuminated dash (reverse video).

You're right about the 10F EGT resolution in normalize mode -- the manual does say that. I was going by my own experience, and it does not seem to be that sensitive. Maybe it's more useful than I thought.

But now, reading the manual more carefully to be sure of my facts , I'm not sure of exactly what features my EDM-700 has, other than that it is a basic unit without fuel flow. But I also have a downloaded manual from JPI that describes a unit they call the EDM-700, which has a much different display and is capable of doing lean find both ROP and LOP. Mine doesn't have that capability. Maybe the difference is a firmware upgrade? In any case I was relying on the downloaded manual when I said that it was possible to download flight data through the serial port. That manual talks about automatic flight data recording. My printed manual (which came with the airplane stuff) doesn't say anything about that, though it has a cryptically written supplement that describes how to download data for import into Lotus 1-2-3. But it doesn't give any internal memory size, or say whether the data is being saved automatically or data recording needs to be activated somehow. So at this point I think I need to call JPI and find out exactly what capabilities my instrument has, and how much it would cost to add the features I need to perform this test accurately enough to be useful.

Even with 1° numeric resolution it's not easy as the EGTs tend to "wander" at least a few degrees when the mixture is constant. That's why the recorded EGT analysis with a constantly changing FF rate is more accurate.

Yes, this is exactly what I found. But I'm not sure how to change the FF at a constant rate. I can only turn the red knob at a steady rate for maybe a few seconds, if that.

There are a couple options to resolve the download issue and I strongly recommend you adopt one of them. The least expensive is a USB to RS232 adapter. JPI sells the Keyspan 19HS adapter they recommend for $50 but I've seen (and purchased) them for about half of that
(http://tinyurl.com/keyspan-HS19). For about $200 you can add a USB port/box to the JPI and with that all you need for downloads is a flashdrive.

Thanks, I'll keep that in mind IF I turn out to actually have a unit that stores enough data to be useful for this purpose.

The expectation is that if one cylinder is running significantly richer than the rest you'd feel the roughness created by that cylinder making way more power than the others. In addition, the "experts" have concluded that unless someone "cleaned" one of your injectors with a stiff wire or otherwise enlarged the opening, it's unlikely you'd ever see one running significantly rich when the others were nearly equal but leaner. I'm not 100% convinced of that but so far haven't experienced anything to contradict it. And if you did have that happen you'd likely see a very noticeable CHT increase on that cylinder compared to the rest which should be cause for further investigation.

I think I need to ask my mechanic some pointed questions then. Last year I had a clogged injector causing a similar, but very persistent rise in one EGT at high power settings, and he DID finally clean it with some kind of sprayed solvent. I'm not sure what else he tried before that, though I recall that he didn't want to use a wire for just that reason. I think it was indeed the injector that ended up on #2 that he cleaned, and #2 is clearly the richest cylinder now.

 

[azure]

What RPM were you running WOT at 7500? I haven't done a serious test like this in my Cardinal. I have tried a "big mixture pull" at 2400 RPM and both 7500 and 8500 feet, right through peak as shown on the GEM bargraph (I have an early model GEM). It doesn't seem to run as smooth as it does at peak or ROP at this altitude, but maybe I am over thinking this slight roughness. The engine runs so much smoother than the flight school 172s I was flying before that maybe I am biased. In any case, I have generally not continued to operate at that mixture, instead enrichening until it is smooth "by ear". And, of course, this is at low power levels, 2300-2400 RPM at 7500 feet or more WOT. IIRC Lycoming says operation at peak is best economy at these power levels.

I was at 2300 RPM for the test, but WOT would have been about 22.5 inches at that altitude, slightly above 65% by the POH so I pulled back a bit to 22 inches. I'm pretty sure that WOT and 2400 at 7500 is above 65% at most temperatures so personally I would hesitate to run like that at peak, or even until smooth "by ear" as at least in my airplane, that's pretty close to peak or even a bit LOP on #3, with the other cylinders possibly still in the "red box". Until now I've been running 100 ROP above 65%, and enrichening to smooth "by ear" at lower power settings. I'd like to be able to run LOP if I can do it safely, to avoid both fouling my plugs and wasting $$$.

I'd also note that as I understand it the fuel "flow" gauge is really a fuel pressure gauge calibrated in flow. It might not even be linear, especially at lower fuel flows. I'd really like to add some real fuel flow instrumentation... someday.

That's my understanding, too.

 

[gismo]

But now, reading the manual more carefully to be sure of my facts , I'm not sure of exactly what features my EDM-700 has, other than that it is a basic unit without fuel flow. But I also have a downloaded manual from JPI that describes a unit they call the EDM-700, which has a much different display and is capable of doing lean find both ROP and LOP. Mine doesn't have that capability. Maybe the difference is a firmware upgrade?

The LOP LeanFind is indeed part of a firmware upgrade but don't bother updating for that as it's pretty much useless. You can use the original LeanFind for LOP simply by starting well lean of peak before activating that mode.

In any case I was relying on the downloaded manual when I said that it was possible to download flight data through the serial port. That manual talks about automatic flight data recording. My printed manual (which came with the airplane stuff) doesn't say anything about that, though it has a cryptically written supplement that describes how to download data for import into Lotus 1-2-3. But it doesn't give any internal memory size, or say whether the data is being saved automatically or data recording needs to be activated somehow. So at this point I think I need to call JPI and find out exactly what capabilities my instrument has, and how much it would cost to add the features I need to perform this test accurately enough to be useful.

They'll want to know the SN of your unit and the current FW revision. IIRC there was a very early version of the EDM700 that did not have internal data storage. You can easily determine if your unit has this ability. Press and hold both buttons for about 5 sec (until the word "Program" appears) and then press the Step button repeatedly while watching the display between presses. If you get to the "END" without seeing the "DUMP ?" text (last one before "END") you don't have data memory. If you do see "DUMP ?" you've got data storage.

Yes, this is exactly what I found. But I'm not sure how to change the FF at a constant rate. I can only turn the red knob at a steady rate for maybe a few seconds, if that.

First, figure out how much you have to turn the mixture knob to get a 1 gph change when you're near the FF that results in peak EGT under the conditions you intend to test. Then divide that rotation by 10 or 20 and make that (small) rotation at fixed intervals of 4-8 seconds (use 4 or 5 if you divided the 1gph rotation by 20, 6-8 seconds if you divided by 10). Since this requires your full undivided attention for a few minutes at a time you should have someone else fly the plane while you do this (or fly while they do the testing).

I think I need to ask my mechanic some pointed questions then. Last year I had a clogged injector causing a similar, but very persistent rise in one EGT at high power settings, and he DID finally clean it with some kind of sprayed solvent. I'm not sure what else he tried before that, though I recall that he didn't want to use a wire for just that reason. I think it was indeed the injector that ended up on #2 that he cleaned, and #2 is clearly the richest cylinder now.

It could be that the other injectors are slightly contaminated if they weren't cleaned at the same time. One scenario I suggested to GAMI that might result in one rich cylinder is having all injectors slightly clogged and cleaning only one. On Continental injected engines the front cylinders are usually the richest if the injectors all flow the same because some of the fuel to the rear cylinders ends up reaching the front ones. I would assume the same would be true for your engine as long as the air supply feeds the intake runners from the rear of the engine. IIRC cylinder 2 is at the front of your engine (Continentals have #2 at the left rear) and if so that might be the only reason your #2 is richest (last to peak going from rich to lean).

 

[AcroBoy]

Gami injectors may have less benefit for smaller engines, like a 360 or even a 470. Likewise, there may be less benefit for a Lycoming versus a Continental due to differences in the design on the induction systems.

You can always switch injectors on the one that peaks first with the one that peaks last, but for the 360 it might not make that big a deal, especially for a small bore Lycoming and lacking an accurate fuel flow meter.

 

[azure]

The manual that came with my EDM does not say anything about a DUMP function. So I assume I don't have it.

Today if it doesn't cloud over (as it's threatening to do most everywhere right now in spite of a SKC forecast -- love those Great Lakes!), I'm going to try it again, manual tweaking method. After changing the EGT resolution to 1F, of course, and I'll check on DUMP while I'm at it.

 

[azure]

Here are my results from today -- manual tweaking method is the only way I could do it, as I confirmed that my JPI does NOT have data recording capability. Note that the FF numbers are off the Cessna analog gauge as I do not have a digital FF meter.

cylinder.......PEAK EGT(F)..........FF(gph)
#3.................1435.................8.7
#4.................1395.................8.4
#1.................1440.................8.0
#2.................1460.................7.9-8.0

I am somewhat suspicious of the absolute temperature values from #4, as it reads cooler than the other cylinders pretty consistently. Perhaps the sensor is miscalibrated? Other than that, the results are consistent with what I saw last week, a spread of about 0.7-0.8 gph FF between the leanest and richest cylinders.

I tried the "rough and dirty" method also, trying to estimate the airspeed difference between peak power and "smooth by ear" LOP. It was very difficult to get consistent airspeed values today because even at 8300 MSL on the altimeter, there were updrafts and downdrafts. I could not really be sure the difference was >4%.

And finally, I confirmed that I can't run #1 and #2 LOP hardly at all without incurring some roughness. IOW the "smooth by ear" point coincides with the peak EGT FF of #1 and #2, i.e. ~8 gph. At higher power levels, if I recall correctly peak EGT is right in the red box. So I'm really not sure I can do this safely with my engine, despite other people's positive experiences with IO360 engines. I wonder whether it would be worth it to try swapping injectors (1 and 2 with 3 and 4)? Otherwise I'll probably continue to lean conservatively at low altitudes and for economy above 8000 MSL. If there's no solution that will let me safely run LOP with my present injectors, I'll still be tempted to look into GAMIjectors, since running 100 ROP most of the time is a huge waste of gas.

 

[gismo]

Here are my results from today -- manual tweaking method is the only way I could do it, as I confirmed that my JPI does NOT have data recording capability. Note that the FF numbers are off the Cessna analog gauge as I do not have a digital FF meter.

cylinder.......PEAK EGT(F)..........FF(gph)
#3.................1435.................8.7
#4.................1395.................8.4
#1.................1440.................8.0
#2.................1460.................7.9-8.0

I am somewhat suspicious of the absolute temperature values from #4, as it reads cooler than the other cylinders pretty consistently. Perhaps the sensor is miscalibrated?

The absolute EGTs have little if any validity, and a difference between cylinders of 100F is common. And if cylinder 4 runs lower CHTs that would by itself generate slightly lower EGTs if everything else was equal.

Other than that, the results are consistent with what I saw last week, a spread of about 0.7-0.8 gph FF between the leanest and richest cylinders.

That can likely be improved considerably with GAMI injectors. A spread of .5 gph or less on a larger engine that burns 14-16 GPH at 65% is considered to be the maximum for smooth LOP operation. On your engine that ought to translate to a max acceptable spread of .3-.4 gph and it wouldn't surprise me if you were able to get it under .2 gph at a single RPM and throttle setting.

'

I tried the "rough and dirty" method also, trying to estimate the airspeed difference between peak power and "smooth by ear" LOP. It was very difficult to get consistent airspeed values today because even at 8300 MSL on the altimeter, there were updrafts and downdrafts. I could not really be sure the difference was >4%.

And finally, I confirmed that I can't run #1 and #2 LOP hardly at all without incurring some roughness. IOW the "smooth by ear" point coincides with the peak EGT FF of #1 and #2, i.e. ~8 gph. At higher power levels, if I recall correctly peak EGT is right in the red box. So I'm really not sure I can do this safely with my engine, despite other people's positive experiences with IO360 engines. I wonder whether it would be worth it to try swapping injectors (1 and 2 with 3 and 4)? Otherwise I'll probably continue to lean conservatively at low altitudes and for economy above 8000 MSL. If there's no solution that will let me safely run LOP with my present injectors, I'll still be tempted to look into GAMIjectors, since running 100 ROP most of the time is a huge waste of gas.

It looks like 1 and 2 are significantly richer than the other pair and swapping them with 3 and 4 isn't likely to make an improvement because the fundamental issue is the fuel from the rear cylinder's injectors ending up in the forward cylinders due to the airflow patterns in the intake manifold runners. Can't hurt to try though, just don't expect miracles.

 

[azure]

Just noticed this reply...

Yes, that's what I was afraid of, I'm going to have to spring for GAMIs if I want to run LOP at higher power settings. Well, it's better to know and do it right than accidentally destroy a cylinder.

Thanks for your help Lance.