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First flight and CHTs

Bill.Peyton

Well Known Member
Wednesday was the first flight of N37CP. Everything went well. I have now flown 5 hours since then. The only issue I have are high CHTs. During climb I see 420 on number 5, with the remaining at 400. In cruise at 3000 ft @ 75% I see 360 on the coolest and 400 on the hottest. They have slowly been coming down with time. Number 5 continues to run the hottest , with 1&2 right behind. I decided to remove the left side vertical air dam. I saw a drop of 20 deg on number 2! It did not have any noticeable affect on 4&6. My plan is to remove the dam on the right side today.
Any suggestions on number 5? It's sealed up tight. My cowl is cut even with the firewall per the plans. Any other experience with the front dams. I see that Tim Olson has his trimmed down

Graph after left air dam removed

CHT.jpg


Graph prior to removal of air dam

CHT2.jpg
 
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Congratulations on your first flight!

At 4 hrs, 125F ROP, 5468' DA, 68%, 55F OAT, OT 185F mine were running 347-388F. If running full throttle and takeoff EGT's, I would have been hotter. Air dams factory height. All built per plans with all new Van's supplied components. My #1 and #2 have always been the hottest, but the difference between them all have became closer with time.

Now at 88 hrs, 40F LOP, 8677' DA, 68%, 55F OAT, OT 200F(because I partially closed oil cooler damper as temps were not getting above 170F then snapped a pic as I always do. Normally try to keep them 180-185F) yesterday we were running 290-314F. No changes to air dams, but did cut slot out about 1 1/2" farther back. The slot did get my 90F climbs over 400F if I did not maintain 115 KIAS or better this summer. I plan on cutting my air dams down a little.

Check your air seals with a flashlight and mirror. With heat and air pressure they should be conforming good by now. I have more written data. These two flight numbers were from pics taken.
 
You'll find that #5 has the same baffle problem that the 360 guys have with #3. A washer or a dent giving a little space behind #5 may well drop you 10-20 degrees on #5. Although I can't prove it drops overall head temp as opposed to just lowering temp at the probe.
 
Your temps are about what I saw on my first flight. Now my hottest runs 360 rop and 330 lop in cruise, and just breaks 400 on a 80 degree day climbing out at 110 kts. I have vans standard setup with new engine.

Items that worked for me.

1). Let the engine break-in and rings seat.
2). Make sure all the holes in baffles are sealed with rtv
3) Cut back both air damns significantly which made big difference reducing #1 and #2 temps. Rest of cylinders did not change much.
4) installed wheel pants and leg fairings. This was worth the most, due to the higher speed of the plane.

Bottom line, I wouldn't worry too much for the first 100 hours and until all pants and fairings are installed. If the front 2 cylinders are running hotter than the back 4, you could start slowly removing air **** material to get them better matched.

Aaron
 
I see! I will try the washers on next flight, if it works, then a removal and a mod to the rear baffle....
 
Congrats on the first flight, Bill. You will get the CHT's under control and if nothing else, it will run cooler as the engine breaks in.

PS I saw this airplane a few days ago and it is very, very nice. Bill does great work!!
 
Congrats!!

Congratulations of getting her in the air:D

I also have high CHT issues with my 10.

What I have found helped most of all is increasing my climb airspeed, second was pulling the RPM back. After I get past the end of the runway, I pull back to 2300, or less, depending on where I am at, and how much of a hurry I am to get to cruise altitude. I try to maintain 140 mph in the climb.

Also, check the area between the cooling fins on the head, the location is below the spark plug, between the valves.

Look to see if there is any obstruction in there from casting flash. This has been a problem for many folks. The air passage between the fins must be clear.

Last, you are nowhere near being broken in, with only 5 hours.
 
Congratulations!

Bill,
Congratulations on your first flight!
By the looks of your charts and description you are well within the borders of other RVs on their first flights.
What's different is, that you have all the advanced engine and data collecting tools at your disposal.
I wouldn't over analize the results at this point before you have accumulated 20 to 30 hours.
Plus 1 for the washer installation behind Cylinder #5 and cylinder#2 it makes a huge difference. I did this on my 8 after initial temps where a little high and installed spacers from the beginning on my 10. I have an MVP-50 engine analizer displaying and collecting data. Looking at the resulting graphs is my favorite thing besides flying.
I don't ever see cylinder temps over 400 and most of the year not even close.
My airdams are all in place just as the baffle kit provides and the only installation difference is the spacers behind #5 and in front of #2 cylinder.
 
Wait.

Bill -

First, Congrats on your first flight! Very cool. You have much to be proud of.

On the CHTs, I cut both my front dams in half early in Phase 1 but did not remove them - on the advice of Strasnuts. My 1 & 2 are still a bit high, but the margin is less. Sean suggested waiting to do anything until after breakin and things level out, which is smart. I learned a lot from Tim's website about sealing baffles and have never had a big CHT problem, even when flying this summer in your country.
 
Bill,

Don't let them go over 420 initially, and later on they should settle never over 380 in a climb, but I did see the same issues at first. Here are some thoughts for you to contemplate, and perhaps a session on skype one evening (morning for me) might be worth doing.

1. Fuel flow on take off should be 25.5GPH to 26 GPH this is for a near sea level elevation and at ISA. Naturally you will see less at higher fields but where you are you will see close to that. The problem I discovered many hours later is the Vans Mixture cable was not long enough and the bracket will flex so as the engine pulls forward on the mounts, the mixture is leaned ever so slightly. As the engine rubbers settle in, this can get worse. So this needs looking at. Your EGT probes I assume are all at the same distance from the head (2-3") and I would expect your raw egt values to be around 1250-1300 if your fuel flow and spark timing is correct (25.5-26GPH and 25 deg)

2. front baffle on the right hand side had the biggest effect for us, YMMV.

3. Do you have a data file I can study?

4.
What I have found helped most of all is increasing my climb airspeed, second was pulling the RPM back. After I get past the end of the runway, I pull back to 2300, or less, depending on where I am at, and how much of a hurry I am to get to cruise altitude. I try to maintain 140 mph in the climb.
I am not in favour of anything mentioned here apart from the last bit, and Mike you could also gain something from this discussion.
4a. Increasing your climb speed, well I use 110-120 mainly because the pitch is too high by pulling back harder, and my CHT in climbs at full weight 348-372 (110KIAS). So early on 120-130 knots should be fine.
4b. Leave your RPM full bore until top of climb unless there is a serious noise issue, then pull back to 2500 for the first thousand feet or so and then back to 2700. Pulling back the RPM to 2200-2300 is simply not a good solution to the problem. Fix the problem, it is not RPM. In doing so you move the ICP and thetaPP in the wrong direction for lower CHT, you will climb slower.

5. Get your gear fairings and spats on, now. The early brake inspections etc should now be over.

6.Dans Link above may help a heap too. After 700 hours and no CHT issues, I have not had the need to look at that but it may well be an issue.

:)
 
There are also a lot of RV builders that are using cooling louvers to aid in CHT temperature reductions. They are easier to install before paint.

If you do decide to go that route, we manufacture them in house and are able to keep our prices very low on them. They are located at

http://www.aircraftspecialty.com/rvall1.html

Have a great evening,
Steve

P.S. On our -10 we noticed a pretty nice reduction in CHT temperatures as the break in progressed. That will naturally occur as the engine breaks in.
 
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David,
My fuel flows are at 25 gph on takeoff and running full rich around 3000 feet at 75% around 18gph. When I try to lean, the chts climb to around 400. I have been afraid to even think of LOP yet.
I have removed both the left and right air dams which resulted in 20 deg. F drop in the front cyl. Number 5 is still the culprit, but coming down, now at 5 hours.
I am going to install the pants and fairings and spats today. I have longer Mixture cable then standard

I don't have skype, but do have facetime on ipad. I will collect some data today and attach it.

Bill
 
I have been afraid to even think of LOP yet.

LOP would ACTUALLY be a better solution, despite the fears and myths of many!

At about 3000' and say RPM anywhere from 2400-2700, dial up about 60 LOP on the last one to peak. Or do a big pull on the mixture knob and richen up until the first one peaks, then back off about 60 or so. Then watch the CHT's drop :):)

Assuming your injectors and induction system are good for it.

HOWEVER.....LOP operations while they are actually a better way to break in your engine, this is not solving the already proven cooling issues. So they still need addressing. And as time moves on, they will get better.

25GPH is about right if you have a DA of 1000' or so, which you probably have had.

Face time, sure thing. Check your PM's
 
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When I try to lean, the chts climb to around 400. I have been afraid to even think of LOP yet.
Bill-

I've been running full rich for the first 16 tach hours b/c my Aerosport break-in instructions indicate I should run full rich for break in. Not really knowing whether or not my engine is broken in, I've been hesitant to use the red knob. I was also reluctant to do so particularly b/c #3 still gets up into the high 380s at 70-75% cruise (Early in phase 1 #3 was around the low 400s/410s). I watched Mike Busch's webinar on leaning on Friday evening and went out Saturday and tried to find out how well peak EGT worked and found that my #3 dropped to the 340s when I went to peak or LOP. (The added benefit is that I went from 9.9gph to 7.7gph and everything still ran smooth.) Still not sure if I should be leaning yet at my stage of break in, but I now know that I'm not going to worry too much about CHT's (within reason) until I start using the red knob more.

Hope this helps.
 
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Steve, if you have been into it hard from the start, 16 hours should have done it.

CHT's start dropping from a point around 40f ROP so yes at peak you will see a drop, however running at peak at high power settings is not ideal. I hope you do not intend to do that for long.

Just because Aerosport say run full rich for break in does not mean you can't do a LOP break in, provided your engine will do it. If you can get your engine to run at 75% power and that is 40f LOP or so you will be fine.

To calculate the 75% LOP in a standard compression engine, HP x0.75 /14.9 = USGPH.

The more you learn about that red knob the better! :)
 
Thanks for the input David. I'm just learning about leaning after having followed the common myths that CFI's tend to teach (e.g. "fuel is cheaper than engines.")

CHT's start dropping from a point around 40f ROP so yes at peak you will see a drop, however running at peak at high power settings is not ideal. I hope you do not intend to do that for long.
Can you elaborate on this? What do you mean by "high" power settings in this context? So far I've only leaned (and only on my last flight) when I've been between 70-75%. From what I understand from Mike Busch, in cruise I want to be somewhere between best power on the rich side, and best economy on the lean side. Peak EGT (or stoichiometric) falls in between. The only warning he gave about where to avoid (within that best power to best economy range) was 40-60F ROP, as that's where the highest CHT's generally reside. I don't recall him warning against flying at peak EGT though.

To calculate the 75% LOP in a standard compression engine, HP x0.75 /14.9 = USGPH.
Handy. Does this formula work for any %? For example, in my 160hp 0-320, at 70% power, would the formula be 160 x 0.70 / 14.9 ?

Thanks again.
 
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75% is high power. If you're going to run leaner than best power it would be best to get 40 F or so lean of peak.
Running at 55% power, do what you want.

With a carb you may not be able to get all of the cylinders to 40 F or more lean of peak without one of them going so lean it quits. Depends on how well balanced the induction is.

BTW, I'm a CFI and I don't tell people to burn more fuel than is necessary. But as you see it takes a lot more education if you want to run moderately high powers with anything other than 125 rich of peak.
 
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Steve, Higher power settings are those generally considered above 75%, no hard and fast rules here OK, just guidelines.

So at 80% power, you want something like 200f ROP or alternatively 60f LOP.

If you are up closer to 90% maybe more like 80f LOP would be good.

To calculate the HP you are producing when LOP take USGPH x 14.9 for a standard compression engine.

Doing HP calc's ROP is a bit more mental maths :confused: but if you wanted a really rough number take off 10% for every 3" MAP multiply that by actual RPM / rated rpm.

It is near enough for most operations.

I could make some other suggestions, but some folk think I am on the take :rolleyes: :D
 
75% is high power. If you're going to run leaner than best power it would be best to get 40 F or so lean of peak.

Steve, Higher power settings are those generally considered above 75%, no hard and fast rules here OK, just guidelines.

So at 80% power, you want something like 200f ROP or alternatively 60f LOP.

Thanks again for your comments. Just to add a little bit to the conversation from what I've learned so far... after watching Mike Busch's leaning webinar, I emailed him to ask him whether or not there were any restrictions to running LOP at higher power settings. I couldn't believe it, but about 15 minutes later he had emailed me back. He must get bombarded with emails, so it was thoughtful of him!

His short but definitive answer is no problem. In fact, he said his turbonormalized Cirrus customers routinely run 85% power and LOP. It's OK to run higher than 75% LOP so long as your CHT's can handle it and, for him, that generally means 380F or below for most aircraft. His only admonition was that the transition from ROP to LOP at high power settings is problematic so that it has to be done either (a) VERY fast [2-3 seconds] using what he calls the "Big Mixture Pull" method or (b) by first reducing to lower power, getting LOP, and then going back up to higher power while remaining LOP.

Moreover, he doesn't generally pay any attention to EGT's to determine where to run LOP. So long as CHTs are OK, just lean to roughness and then back to smooth. Doesn't matter where it might be between stoichiometric/peak EGT and best economy.

I know not everyone agrees with Mike Busch, but just thought I'd pass along what I learned from him.

And again, to get back to the original poster's question, I was amazed at how messing with the red know really changed the CHT's (for the better).
 
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Cool, that is great info.

I have gradually been going LOP earlier and earlier after takeoff and now go LOP with a BMP (big mixture pull) at 1000ft then do a shallow climb. I have been reducing MAP to 23" or so before the BMP but given Busch's statement, I will try doing the BMP without the MAP reduction and see what happens.

I typically see CHTs go from 360 to 380 or so down to 300 to 320 after the BMP. I couldn't pour enough gas to get an equivalent CHT drop on the rich side. The effect on fuel has been huge.

Also, i notice on my last 5 hours after the oil change, the oil is still amber colored and still looks like new. I have never seen my oil stay amber for so long. I am thinking that can only be good for the engine, too.

Jae
 
I have been reducing MAP to 23" or so before the BMP but given Busch's statement, I will try doing the BMP without the MAP reduction and see what happens.
Glad it helps, Jae, though I would mention to be sure to take his comments about leaning at high power settings in context of his entire presentation on leaning. http://eaavideo.org/video.aspx?v=994986557001 His general recommendation is to stay ROP while in a significant climb and then only go to LOP thereafter. While climbs can be done LOP, he comments that they are trickier. Good luck with your experimenting.
 
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His only admonition was that the transition from ROP to LOP at high power settings is problematic so that it has to be done either (a) VERY fast [2-3 seconds] using what he calls the "Big Mixture Pull" method or (b) by first reducing to lower power, getting LOP, and then going back up to higher power while remaining LOP.

It's not actually all that problematic for us.

Take a look at the first and second dyno charts here:

http://www.vansairforce.com/community/showpost.php?p=566697&postcount=81

The first chart is roughly 27/2700, certainly a high power setting, and pretty much what you would have with prop and throttle full forward after a few minutes of climb. Note there is no evidence of detonation at any mixture setting, even with test temperatures at maximum. You could pull the red handle as slow or as fast as you please. This is the reality of a standard compression NA Lycoming...you can't detonate it with the mixture knob while running even or undersquare. BTW, this is also the simple reality behind the recently reviewed Lycoming SI for leaning at Embry Riddle.

The second chart is 28.5/2700, i.e. leaning near sea level, or leaning a turbo-normalized engine anywhere below critical altitude. With high operating and intake temperatures it shows light detonation from about 60 ROP to about 50 LOP. Detonation during 10% of combustion events isn't likely to hurt anything, and at normal temperatures it may not detonate at all. Still, a conservative pilot (or engine guru) might prefer pulling through the pro-detonation range quickly. Personally I think it a pointless issue with stock NA installations in RVs. To have maximum possible manifold pressure you would need to be on the deck, and if at full RPM you must be trying to go like stink. Why reduce power with a LOP mixture? Run at max power mixture, well rich of the detonation range.

Usual disclaimer...higher compression or advanced timing makes you an experimenter, although the general trends are the same.

Now back to the original thread theme, high CHT. It is good to know how to exercise some limited control over CHT with the mixture knob. However, after break-in the installation should be capable of cooling the engine at full rated power. If it will do not do so, there is a design or fabrication problem. Power reduction (by mixture or otherwise) is just a crutch.
 
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Here is a summary of todays experiments. I have removed both front air dams, this has lowered #1 and #2 by almost 20 deg F. They are now within + - 5 degrees of all cylinders but #5. I then put a washer under the right rear outside attaching screw to space the rear baffle away from the top part of the #5 cylinder. In addition, I used the threaded rod, which holds the lower wrap-around lower baffle to the bottom of the #1 and #5 cylinder, to separate and develop a 1/4" gap around the #5 cylinder. After a short flight and recording the data it appears that this has reduced #5 by almost 10deg. F.
It is my opinion that the #6 cylinder is cool because the oil scat tube outlet is on that side and is allowing the flow of air across the cylinder. The #5 cylinder only has a small opening in the rear baffle for the heat muff supply air. Tomorrow I am going to open the rear baffle at the lower area another 1/4" and see if that gains more improvement. I now have 8 hours on the engine and looking back at the data, I can see a marked improvement in all of the CHTs, but at this point I am still unable to lean to 150 deg ROP without increasing #5 to 400 Deg. When I do the big pull to LOP they all drop to under 350 Deg. with the hottest EGT 40 deg of peak. Any more than that and the engine gets rough. I will flow match the injectors after break in, which should hopefully fix that issue.
 
Bill,

I am not sure what your idea about getting to 150 ROP and having low CHT's is based on. At the kind of power settings I assume you are talking about, this is not surprising, and not an ideal place to operate.

And I do not support Mikes blanket statement on so long as CHT is below 380 either. That all depends. Now we most likely are not all in Alaska in the middle of winter, but you can get CHTs there at 380, and do some less than kind things to an engine. But in general terms if you are doing nice things to your engine, you will be under 380 anyway. :)
 
But we could all use a little charm school eh Dan? :)

Thanks for reposting the detonation limit testing charts..this is DATA and USEFUL!
 
the installation should be capable of cooling the engine at full rated power. If it will do not do so, there is a design or fabrication problem. Power reduction (by mixture or otherwise) is just a crutch.


Thas rite. :)
 
Dan, maybe he might, but that setting and a low CHT at the same time, well those two tend to not happen together do they? But you knew that already. Can't have cake and eat it too!

I am not going to put the words in the mouth of the APS guys, you can try, but they have not posted here for over 5 years, so I would not hold your breath ;) but at a quick glance it does not seem to be something they would endorse. Maybe its the scales or something, I'll look later with a decent screen, but it looks a bit odd to me. EGT and CHT being so linear for a start, the top of the power curve?

Which Turbocharged Lycoming is this from out of interest. Remember they have LOTS of Turbo Lycoming data.
 
Dan, maybe he might, but that setting and a low CHT at the same time, well those two tend to not happen together do they?

No problem with my airplane.

... but at a quick glance it does not seem to be something they would endorse. Maybe its the scales or something...

General relationships to mixture. Remember these?

1zyitki.jpg


zv7bqf.jpg
 
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Yeah.....on the rich side of peak the EGT and CHT the relationship of those last two are vastly different to the first one you posted above :confused:

The TCM one and the APS one look a lot more familiar :) And which ones are you backing? The first one? or the last two?

:)
 
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However, after break-in the installation should be capable of cooling the engine at full rated power. If it will do not do so, there is a design or fabrication problem. Power reduction (by mixture or otherwise) is just a crutch.

Agreed 100% Dan, and hence my comment on page two and in emails with Bill, the comment....
HOWEVER.....LOP operations while they are actually a better way to break in your engine, this is not solving the already proven cooling issues. So they still need addressing. And as time moves on, they will get better.

You need to sort the cooling issues for all modes of operation. Reducing RPM, MAP or using LOP is only covering up a built in problem.

At least we agree on some things, most actually.....:)
 
Yeah.....on the rich side of peak the EGT and CHT the relationship of those last two are vastly different to the first one you posted above :confused:

They look the same to me. Read them again. The lycoming chart has CHT in Centegrade and EGT in F. dont know why but they do.

Both engine manufactures data showes that it is perfectly acceptable to operate in excess of 400F CHT.

Unless data showes otherwise why does so many people preach 380, 400 or some other number as "DO NOT OPERATE THERE"?

It is like some automobile mechanic preaching "NEVER EVER PRESS THE ACCELERATOR TO THE FLOOR AND HOLD IT THERE"!

Look! The engine was designed to handle it for climb out. Just like a car was designed to take the full throttle acceleration to max speed without problem.

If you keep it cooler it will maybe last longer, maybe not. Definantly easier on the parts but no garantee it will last longer. I seriously doubt most Lycoming problems are coming from letting CHT's get above 400 during climb out.

I have had extended conversations with ECI about CHT and they have no problem whatsoever with cruising in the 420-430CHT range.

I personaly do not operate there but that is because I plan to "take it a little easier on my engine than it was rated for".
 
Unless data showes otherwise why does so many people preach 380, 400 or some other number as "DO NOT OPERATE THERE"?

The higher your cht's, the greater chance of having cracks develop. I overhauled jet engines for awhile, I now work on gas furnaces and heat pumps. Thermal cycle count and temperatures have a great effect on parts longevity.

Look! The engine was designed to handle it for climb out.
I always keep that in mind in case I ever need it, but so far I have preferred to keep the nose down for better visibility, safety and cooling.


I have had extended conversations with ECI about CHT and they have no problem whatsoever with cruising in the 420-430CHT range. I am sure they as well as Lycoming don't have a problem since we will be going back to them for their $1000+ cylinder heads.

I personaly do not operate there but that is because I plan to "take it a little easier on my engine than it was rated for".Same for me...at 380F I start lowering the nose.

There are many ways to run or ruin our engines. Break-in is the most critical time because you want just the right amount of heat and pressure. They are pretty well built or we would have many more failures than we do. I always try to be gentle with any power/temperature changes, lean except for takeoff and pull the prop back to 2100 for the descent.
 
Yeah.....on the rich side of peak the EGT and CHT the relationship of those last two are vastly different to the first one you posted above :confused:

Perhaps you could point out the specific differences?

The TCM one and the APS one look a lot more familiar

The Lycoming chart is unlikely to be a handout at APS. It is the cover illustration from a publication called "Experts are Everywhere to Help You", Lycoming's very poor attempt to argue leaning technique with George Braly.

I do want to hear about the vast difference you see. In the meantime I'll cheerfully state all three charts illustrate the same fundamental relationships between mixture, power and temperatures. In the context of this thread, it is clear (1) you can't run LOP and get rated power, and (2) if you want rated power you must build in the necessary cooling capacity.
 
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Dan,

I am using my Macbook Air screen at the moment and maybe it is the scale of centigrade for CHT vs EGT in F, or my eyesight, but I have a hard time seeing that on the Lean side of peak we have a diverging egt and CHT trace in all three graphs, yet on the Lycoming graph at the top it shows perfectly parallel traces on the Rich side, yet the TCM and APS graph are more consistent with everything else I have seen.

Like I said maybe its the scaling or maybe its just a marketing graph, with no other scientific purpose. I assume you know why? I really can't be bothered finding out, I am busier than ever doing work on multiple fronts to second guess what this publication was about.

In the context of this thread, it is clear (1) you can't run LOP and get rated power,

No kidding :D:D Anyone looking at the graphs should be able to work that out especially with a NA engine. However get a Turbocharged engine and you can.....and do even more......but that is thread drift right out there....lets stop here! ;)

and (2) if you want rated power you must build in the necessary cooling capacity.

Is that not what I said in my last post, although you have put it in words far more eloquently than I:) did. Looks like we are agreeing again! :eek:


And while we are having a bit of fun.....here is GB having a little fun after said article was written
pp42_braly.jpg
 
....on the Lycoming graph at the top it shows perfectly parallel traces on the Rich side, yet the TCM and APS graph are more consistent with everything else I have seen.

The Continental rich side traces are chopped off. For example, the full range of graphed EGT is only about 130F, while the longer trace on the Lycoming chart covers a range of 350 or so.

The missing portion of the Continental EGT/CHT traces may or may not be parallel. Doesn't matter. These charts are merely illustrations of general relationships....trends and landmarks. The actual traces shift around slightly depending on MP and RPM.
 
and to compare one chart to the other would require a detailed understanding of the test configuration and method of test for each.

CHT for instance is a function of not only the combustion process but also the cooling flow. How was cooling flow established during Lycoming, APS and TCM engine testing? Was it a constant mass-flow arrangement or did they vary mass-flow as a function of Hp to represent flight conditions?

As installed in a particular aircraft I would not expect to duplicate CHT plots precisely because of cooling configuration differences...but as Dan says, the relative trends are important not absolute values.
 
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