So I have 110hrs on this engine now in my 206. The rear 2 cylinders run consistently cooler then the rest. Seems to be the reverse of what usually happens. Any ideas on that?
Also curious what you guys think of my temp spreads? Is it super important to have them tighter then that? If so, what does tighter grouping give me? Longer engine life?
Thanks.

My experience with the big six cylinder continentals is that the forward cylinders run hotter and the rear cylinders run cooler. My hottest cylinder is usually 5 which sits behind my oil cooler. Also, you are running your engine in an interesting way with your fuel flow on the low side for ROP operations and on the high side for LOP operations at that MP and RPM. Or are you running a 470?

Based on your questions on temperature spreads and longevity, I believe you might benefit from the course by Advanced Pilot Seminars. https://www.advancedpilot.com/

Squash wrote:My experience with the big six cylinder continentals is that the forward cylinders run hotter and the rear cylinders run cooler. My hottest cylinder is usually 5 which sits behind my oil cooler. Also, you are running your engine in an interesting way with your fuel flow on the low side for ROP operations and on the high side for LOP operations at that MP and RPM. Or are you running a 470?

Based on your questions on temperature spreads and longevity, I believe you might benefit from the course by Advanced Pilot Seminars. https://www.advancedpilot.com/

This is an IO-520. Very close to LOP. But I'd be happy to run it at less. I can get about 10.7 GPH but it is not Smoot at that anymore. According to the lean find feature 11.5 is LOP. I've been very happy with that economy and setting when comparing with the same engines that have GAMIs and tuned exhaust. Our numbers are very close, although their temp spreads are a bit tighter.
Thanks for the link, I'll check it out.

5 and 6 are the cool ones on my 520 in my 180. I do see at least a 30-40 degree delta between my hottest and coolest cylinders. The only limits that are specified in the TCDS are the are maximum cylinder head temperature.

My operating strategy for running big bore continentals is to lower the nose or open cowl flaps if I see a CHT approaching 380F-390F. I am very careful not to cross the 400F mark.

I don't know if there are any adverse results for having CHTs down around 270F, but I believe that the properties of most steel and aluminum alloys are pretty stable in th2 200-400 range.

I’m curious...are you using Gami injectors? If not have you tried swapping the hottest cylinder injector with the cold cylinder?...And what is the minimum CHT for lead precipitating and fowling the plug? Impressive fuel flow rate! The IO520 permold I built for my experimental has no RPM restrictions with the prop counterweight configuration.....it has Gami’s...hope once the Bearhawk is done my flow rates are as good as yours...


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m_moyle wrote:I’m curious...are you using Gami injectors? If not have you tried swapping the hottest cylinder injector with the cold cylinder?...And what is the minimum CHT for lead precipitating and fowling the plug? Impressive fuel flow rate! The IO520 permold I built for my experimental has no RPM restrictions with the prop counterweight configuration.....it has Gami’s...hope once the Bearhawk is done my flow rates are as good as yours...


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I'm not running Gamis. I have swapped injectors and it didn't make any noticeable difference. I guess that's maybe my real question. Are my temp spreads close enough? Or should I invest in Gamis to get them closer. It's a lot of money to spend if all I am doing is bringing my spread closer for nothing more then visual purposes. If it will help my engine last another 500hrs then it's worth it, if it's just to level out my bar graph I'm not sure it is...
I've always thought that EGT is more important then CHT for lead fouling. My plugs have been staying fairly clean running at these settings, so again I've been happy with that.

I don’t know if the expense of GAMI injectors is worth the fuel savings you may gain. Your cold cylinders are probably running a little rich.... Gami will probably lean your cold cylinders...wonder if they ever finished their prism system...haven’t heard anyone talk about it?


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I have never seen the back 2 ever being close to cold..... I would "trust but verify" that the probes are where they say they are. Heat gun to the probes should do the trick.

GAMIs are intended to balance EGT(for better LOP operation), not CHT.

With a 520, and running your fuel flow at that rate, yeah, you are getting into the lower power zone. I would guess that you might be in the peak EGT rather than LOP at that MP setting. If I'm running that fuel flow and RPM, my MP needs to be up around 25" to get me on the lean side. But it probably doesn't matter what you do at that fuel flow because you likely can't hurt anything.

If you were to keep 23 squared and bump your fuel flow up to the ROP side at say 15-16 GPH, I think you will find that your #1 and #2 cylinders will get hotter and the spread across all cylinders will be less. This is because they will be generating more power (get hotter) and excess fuel flow will help to cool them (more even cooling), and there will be less discrepancy between heat and cooling across all cylinders.

When you are running LOP, there is no excess fuel helping to cool your cylinders and cooling becomes much more dependent on airflow which is more variable across your cylinders. The rear cylinders get more airflow typically and stay cooler than the cylinders up front.

Regarding GAMIs, they will become useful only if you aren't able to achieve a satisfactory LOP fuel flow due to engine roughness. This roughness is created with unequal power output from each cylinder due to fuel flow mismatch. GAMIs will match each cylinder to Peak EGT as closely as possible. And when you start down this path, you will realize that the "temperature spread" between actual egt temperatures is not important. The temperature spread between CHT's is not that important either as long as you feel that your CHTs are warm enough to keep your valves guides from gumming up.

Awesome info Squash. Thanks for that. I've just read a few things lately that keep talking about having all your temps even and wasn't sure how close they needed to be. I really wasn't super concerned, just thought I'd ask.
I am curious what you run for fuel flow at 23 Sq? At 7500' and that power setting I can maybe squeake out 10.7GPH, but it does start to have a noticeable stumble anything less then that. Even anything under 11 sometimes I get a stumble. I haven't heard many guys that are running 520s down around 11, which is why I've been happy. But I'm always up for learning.

Good post by Squash. As he said I’d first look at temps ROP and compare. Like all levers full forward (initial climb) if your cold cylinders become your hot ones, then you probably have a nozzle imbalance and should proceed with the GAMI lean test.

Tangogawd wrote:I have never seen the back 2 ever being close to cold..... I would "trust but verify" that the probes are where they say they are. Heat gun to the probes should do the trick.

GAMIs are intended to balance EGT(for better LOP operation), not CHT.

Those temps look almost exactly like my IO-520, except in the opposite order (my #6 is the one in the 200s). I’m routinely running sub 11 gph LOP, but mainly due to being based at 5000 ft with terrain around so mostly flying 8-10k. I’ve got GAMIs, but doubt you’d see a financial gain by installing them. With the close balance, my engine never really gets rough as I go more LOP, it just stops making power.

If I'm up at an altitude where WOT gives me 23" of MP, so let's say up at 6500', then I'm usually in the 10.5 gph range. When I'm on a cruise descent, I will often dial my MP back to 20" and roll the fuel flow to 9 gph.



If you are interested in learning more about the theory behind engine management but don't want to spend the money on the APS courses, you could read all of the Pelican Perch articles pertaining to engine management. https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-index/

You will learn why the absolute value of EGT is not important, and therefore, why considering the EGT spread is useless. GAMIs do not "equalize" EGTs.

You will learn that MP at a fixed fuel flow controls mixture. This is why when I'm flying in the sub 6000's, I usually run 11.5 gph at 2300 and increase my MP to about 25". This seems to be the sweet spot for me when my richest cylinder is about 50 deg LOP.

Running LOP requires that your ignition system be in good shape. It is much harder on your ignition system to light the flame in your cylinder when LOP, whereas a delipidated ignition system with tired plugs can usually run an engine ROP that wouldn't fire LOP. Those occasional engine stumbles might be related to something in your ignition system. You can try to challenge it by doing a mag check on the ground and comparing the check when rich versus lean. I think Deakin in one of the articles describes doing mag checks in the air and also goes on to describe the appropriate procedure for restarting your engine should it quit because you would not want to simply switch your mags back to both like your instinctive reaction might command.

Anyway, there is a lot of good stuff in there.

Get Gamis! They are worth it. At what altitude are you seeing that “LOP” fuel flow? I question if you are really lean of peak. LOP in my IO-520, I’m seeing 10.0-10.5 gph around 5-7k’ decreasing to low 9s to high 8s above 10K’. All temps in the mid to low 300s unless it’s winter time and then a few dip into the high 200s. If I remember eight you don’t want to get them colder than 27-280. I forget the exact reason. Something about the lead scavenging or something. Watch Mike Busch’# videos on leaning and his follow up on LOP ops.

Lower CHTs do extend life via lower internal pressures, temps, etc. mike covers this stuff too. For $900 gamis are a must, especially if you want to run LOP.


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Grassstrippilot wrote:Get Gamis! They are worth it. At what altitude are you seeing that “LOP” fuel flow? I question if you are really lean of peak. LOP in my IO-520, I’m seeing 10.0-10.5 gph around 5-7k’ decreasing to low 9s to high 8s above 10K’. All temps in the mid to low 300s unless it’s winter time and then a few dip into the high 200s. If I remember eight you don’t want to get them colder than 27-280. I forget the exact reason. Something about the lead scavenging or something. Watch Mike Busch’# videos on leaning and his follow up on LOP ops.

Lower CHTs do extend life via lower internal pressures, temps, etc. mike covers this stuff too. For $900 gamis are a must, especially if you want to run LOP.


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Hey Corey. I'm at 5500 on that flight. It was a winter flight so probably why it's a bit cooler. Up at 7500 I can get it down to 10.4 usually.

A1Skinner wrote:So I have 110hrs on this engine now in my 206. The rear 2 cylinders run consistently cooler then the rest. Seems to be the reverse of what usually happens. Any ideas on that?
Also curious what you guys think of my temp spreads? Is it super important to have them tighter then that? If so, what does tighter grouping give me? Longer engine life?
Thanks

Skinner,

I'm battling the opposite problem with #1 in my 206.

Tim

Hello A1

Curious, did you try running your engine rich as Squash suggested to see if your rear Cyl became the hottest ones?

Scolopax wrote:

I don't know if there are any adverse results for having CHTs down around 270F, but I believe that the properties of most steel and aluminum alloys are pretty stable in th2 200-400 range.

I remember reading in some TCM literature that the preferred minimum was 300, but I don't recall where. I'll poke around a bit and see if I can find it. It may have been in the operators manual.

[email protected] wrote:Hello A1

Curious, did you try running your engine rich as Squash suggested to see if your rear Cyl became the hottest ones?

They warm up if I run full rich, but they still aren't the hottest ones.

Grassstrippilot wrote:Get Gamis! They are worth it. At what altitude are you seeing that “LOP” fuel flow? I question if you are really lean of peak. LOP in my IO-520, I’m seeing 10.0-10.5 gph around 5-7k’ decreasing to low 9s to high 8s above 10K’. All temps in the mid to low 300s unless it’s winter time and then a few dip into the high 200s. If I remember eight you don’t want to get them colder than 27-280. I forget the exact reason. Something about the lead scavenging or something. Watch Mike Busch’# videos on leaning and his follow up on LOP ops.

Lower CHTs do extend life via lower internal pressures, temps, etc. mike covers this stuff too. For $900 gamis are a must, especially if you want to run LOP.


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This is at 5500 feet the other day. Still running nice and smooth at this setting. 40 degrees LOP.