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High CHTs

J

jimgreen

Well Known Member
Now summer has arrived, my CHTs are making me squirm.
At an OAT of around 25 I get 420 to 430 in an extended climb which drops in cruise to 360 - 380 at 75%.
The engine only has 40hrs and oil consumption is around 1qt per 10 hrs.
Nickel carbide ECI cylinders. IO360 C/S on a 7.
I've read the article by ECI on the effects of excessive CHTs.
I've also read on a recent thread that Lycoming is not too concerned below 440 due to modern metallurgy.
My question is, What is normal and acceptable for an RV?
Can I expect temps to reduce over time? I know gear fairings will help a bit.
I'm working on my baffles of course.
 
I live and operate in a hot place. You should not accept climb temps above 380.

Either your installation is wrong, or your operation is wrong.

Is this the CHT screw in or spark plug probe?

Make sure your fuel flow is correct at ake off, make sure your leaning in the climb is correct, and make sure your cruise settings are good.

baffles are most important. Plenty of reading material here about that.

David Brown
 
The info I got from a forum by Mike Busch at OSH11 was that 380 should be the acceptable limit and 400 absolute max.

I usually have to throttle back and limit the climb rate shortly after takeoff to keep it under these numbers. If the engine is already hot, say from a quick land-refuel-takeoff, I have to start throttling back almost immediately after takeoff.

I've been wondering if this is normal or if I need to look into redoing my baffles. Engine is 160 HP O-320 in RV-6A
 
but what data supports these assertions of 380 or 400 when the engine designers say otherwise?
 
--------------------------------------------------------------------------------

but what data supports these assertions of 380 or 400 when the engine designers say otherwise?
Click to expand...

Just plot a graph with CHT versus longevity. You will notice that if you leave the engine pickled in a cold garage the cylinder life goes to infinity. Jeez guys they're just chunks of aluminum, not the crown jewels.
 
RE: Graph ????

aerhed said:
Just plot a graph with CHT versus longevity. You will notice that if you leave the engine pickled in a cold garage the cylinder life goes to infinity. Jeez guys they're just chunks of aluminum, not the crown jewels.
Click to expand...

Where can I access this graph or graphs from multiple sources?
 
I was just kidding about the graph. Its hard to plot infinity (takes a really big sheet of graph paper).
 
Funny.

The OP is looking for help and asking questions about his CHTs and he gets arbitrary calls for limits far lower than the engine manufacterers detail.

If 380 is a limit I'd presonally like to understand how the number was determined and at least a description of the analysis undertaken in its derivation. Otherwise I think the CHT limit should be 357.3 in cruise and 379.7 in climb any temps higher than these requires a complete overhaul or factory new engine ;)

Follow the manufacter published limits and operating procedures and your engine should reach TBO and beyond all things being equal.

If you are concerned about CHTs (no matter what their value) the most important check is for leakage of baffling. In RVs the inlet area often needs the most work. Adding wheel paints and fairings will help CHTs in cruise for a given power setting but do nothing for climb CHTs if compared at the same climb airspeed, although you will climb faster getting to cooler air quicker. Therefore the CHTs may cool off sooner but will probably still peak to near the same values.

Your prop configuration will also affect climb CHT due to blade root chord, planform and airfoil. Changing from a Sensenich Wood 2 blade to a Catto 3-blade resulted in at least a 20 deg avg climb CHT reduction across many, many flight tests under very controlled and documented flight conidtions.

inlet/exit ratio affects mass flow which in conjunction with OAT determines cooling capacity. see many threads on this topic for details.

if you have a carb engine how tight is your lower cowl to FAB seal? Leakage here can over pressurize the lower cowl and reduce mass flow (mass flow is a function of Upper to lower cowl pressure)

The true benefit of working to reduce CHTs far below manufacters limits is to increase the margin available for a full out drag reduction program which will tend to raise the CHTs toward those limits again, such as thottling the exit area.
 
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RV8R999 said:
but what data supports these assertions of 380 or 400 when the engine designers say otherwise?
Click to expand...

Dont have a web reference at my fingertips for you, but somewhere in the Deakin articles there is a graph showing relatively rapid drop off in the strength of aluminum at about 400 degrees, although its a bit subjective exactly where to draw the line. It would certainly seem that changes in the alloys would affect the graph, but I have not seen any graphs and data that support a value above 400. Not saying it doesnt exist, but to me, the onus is on the engine companies making the claims for higher temps to provide this data, not the other way around. It is reasonable to me that, other factors aside, lower temps would correlate with longer life, so when I see my temps creep above 400, I lower my nose until the temps come down.

erich
 
RV8R999 said:
but what data supports these assertions of 380 or 400 when the engine designers say otherwise?
Click to expand...

for me, it's just that Mike Busch specializes in maintaining these engines and seems to know what he's talking about. Before I went to his forum, I didn't know any better, and just left the throttle all the way in until I was at cruise altitude. According to Mike, that's not at all good for the engine, so now I monitor CHT all the time and limit it accordingly.
 
erich weaver said:
Dont have a web reference at my fingertips for you, but somewhere in the Deakin articles there is a graph showing relatively rapid drop off in the strength of aluminum at about 400 degrees, although its a bit subjective exactly where to draw the line. It would certainly seem that changes in the alloys would affect the graph, but I have not seen any graphs and data that support a value above 400. Not saying it doesnt exist, but to me, the onus is on the engine companies making the claims for higher temps to provide this data, not the other way around. It is reasonable to me that, other factors aside, lower temps would correlate with longer life, so when I see my temps creep above 400, I lower my nose until the temps come down.

erich
Click to expand...


it is absolutely true the alloys in our engines have reduced yield at higher temperatures..this is a matter of the physical properties of most, if not all alloys. The designer takes this into account and compensates by increasing the material thickness acording to the local forces which will be present under worst case conditions plus some margin. Knowing this and the manufacteres tested and designed limits should give everyone comfort that although the metals have reduced strength, the strength remaining is greater than needed to operate safely for the life of the engine when operated at or below those published limits. Operations below those are simply for happiness and bragging rights.

If the designer wanted to minimize the margins and design with much reduced CHT limits it would be possible to produce a very light weight engine but without any room for construction or installation variances.

I agree reducing CHTs is a worthy effort for myriad reasons but espousing made up limits without supporting data isn't helpful to anyone.
 
RV8R999 said:
I agree reducing CHTs is a worthy effort for myriad reasons but espousing made up limits without supporting data isn't helpful to anyone.
Click to expand...

Agreed; my point is that Ive seen more real data (and logic) from Deakin/Busch than I have from the engine manufacturers. So, Im erroring on the conservative side and sticking to a 400 degree limit until Im shown convincing evidence to the contrary. Its got to be more than just empty words on a page saying you're good to 500 degrees or whatever

erich
 
I'm kind of busy today so I won't be able to follow the thread as closely as I otherwise would.

Would someone just email me when a knowledgeable source weighs in with actual data and sources, rather than "I heard once" stuff. Preferably with links and data?
 
LettersFromFlyoverCountry said:
I'm kind of busy today so I won't be able to follow the thread as closely as I otherwise would.

Would someone just email me when a knowledgeable source weighs in with actual data and sources, rather than "I heard once" stuff. Preferably with links and data?
Click to expand...

Good luck Bob, there isn't any, just theories.....from the same people that tell you if you run in the "red box" your going to detonate, yet, so far, and I have challenged this large and fine group of people, nobody has found one example of an RV destroying an engine by detonation, and you can't tell me people don't run there all the time, by accident or otherwise. Please, somebody prove me wrong.
Running in the box is not wise or good. Running high CHT's is not wise or good either. Now, what that is seems to be the matter of discussion.

I worked and worked on my baffles, including reworking my ramps. Now I cool so well I have to be careful not to shock cool even doing something simple like slowing for pattern entry.
Meanwhile, my 2300+ hour 0320 in the Bucker, with one CHT probe, chugs along just fine and has never been topped. Who knows what the CHT's are really doing up there....
I think it is great we have all of this wonderful instrumentation to analyze everything to death, but it sure prompts a bunch more discussion.
 
Don't say shock cooling, you'll start another war!
But seriously, does anyone know why TCM and Lycoming publish different red lines for CHT? Do they have significant differences in the alloy?
 
C-FAH Q said:
Leaning in climb will increase temps. Fuel flow helps cool, don't lean in climb.
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I have found that leaning in the climb does help CHT temps, maybe im doing it wrong. LOP, less fuel, less bang, cooler temps.

I also try and climb with a min speed of 100kts in the summer, if I climb at say 80 kts with the nose point up, I will see over 400 CHT.
 
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fstringham7a said:
So Bob here is the man who MAY have the last word?????? Flame suit on adjusted and readynformanynandmall incoming fire:eek:

http://www.avweb.com/news/pelican/pelicans_perch_84_mixture_cht_194816-1.html
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I find it interesting that he apologizes for the previous articles he wrote on the subject "contributing to the confusion". I still value his articles. I just choose to use my own good judegment and take them with an educated grain of salt. I think he is advocating that if you read between the lines. No two set ups are the same.
For what it is worth, I follow what he preaches, even before he preached it. 420 is my max. limit, 400 is my "watch it", and my cruise CHT's even in high ambients are 360 or less, usually way less.
I have no worries about the longevity of my engine.
 
I was completing my V-speed testing the other day in order to determine Vx and Vy. It's 85 degrees. You can't climb at 65 or 60 knots to complete the lower end of the graph and not go above 400...or,in my case, well above 400. Granted it was only for two minutes.
 
Here we go again. The same old shots from the hip, like where do you get that from, where is the data....Well there is plenty of data, it supports the case, and it MUST BE REMEMBERED the numbers are not hard 380 +/- 0.005 F

You guys need to lighten up a little, more importantly, you need to understand that I can't nor can anyone else present a full education on VAF, not in one post, not in one thread, not in a thousand posts. education simply does not work that way.

Interesting to note, that while having a debrief session recently with John Deakin, Walter Atkinson and George Braly on the topic of how best to educate, it was noted that to the best of their memory, not one RV owner has flown to ADA OK for an APS seminar. Maybe some have been sneaky and gone in by stealth, but we did discuss why so many Cessna/Beech/Piper owners take the time and spend the money yet the RV community does not. I have my opinion on why, and they seemed to think it was plausible, but none the less an interesting issue.

So in one post, or even a few can I give you everything you ask for, no. But I will do my best to cover a few points from the last three pages.

C-FAH Q
Quote:
Originally Posted by RV10inOz
make sure your leaning in the climb is correct,
Leaning in climb will increase temps. Fuel flow helps cool, don't lean in climb.
Click to expand...

Clever username, surprised you got away with it!

Read exactly what I said again, Make sure your leaning in the climb is correct. Not leaning in the climb is incorrect. Do some research on John Deakins articles, In The Climb, no point me reprinting it here.

I see Jamie Lee has mentioned LOP climbs, climbing LOP is a valid method, I would caution everyone about doing this unless you have been trained to do it or are suitably educated. ROP climbs are easy when done by the Target EGT method. In a Turbo (TC or TN) a LOP climb is easy, but so are ROP climbs, in a TN you just touch nothing!!

RV8R999
Quote:
Originally Posted by RV10inOz
I live and operate in a hot place. You should not accept climb temps above 380.
Where did you come up with 380?
Click to expand...

I just plucked a number out of my ####, seriously, it is another fuzzy number, but one from looking at data, and while CHT is affected by ambient so you should NEVER use a CHT as a target, like you do an EGT, when you look at the ICP's (cylinder pressures) and temperatures, the two things that are always attacking your engine are temperature and pressure. It is not a sudden destruction we are talking about, it is about going to TBO and maybe 1-2000 past TBO. When you look at the strength of the alloy, the temps at which properties change, and what the ICP's are when you have high temps (you get high temps when you have high ICP) it is really easy to say....lets aim to stay below 380. I can't easily, and won't post all the stuff here, it just won't fit, but you can obtain this and see it for yourself if you want to.

but what data supports these assertions of 380 or 400 when the engine designers say otherwise?
Click to expand...
And what exactly do they say??? They rarely say the same thing twice, and often contradict themselves and each other. Its your engine, use 500F if you prefer!

The cylinders will have a far better chance of a long healthy life if you keep them cooler and a workable fuzzy limit is around 380, plus or minus 10-20 or what ever you are happy with.

fstingham7a
Where can I access this graph or graphs from multiple sources?
Click to expand...
Not many places I am afraid, but here again, just one or two snippets of info is not enough. Attend an APS course and they will give you all you need and it is valid info from any of the tested to be true sources.

Frank finally, that article you posted the link to is a very good one, earlier in this post I mentioned not using CHT as a target, and JD explains this well.

Enough for today! :)

All the best!

DB

PS Letters..... a couple of minutes once in a while is not instant death, but if you want really good life and low costs, you would not stay there all day, hour after hour for hundreds of hours would you? Of course not. This is the whole point, some folk just fail to see the woods for the trees!
 
brian said:
The info I got from a forum by Mike Busch at OSH11 was that 380 should be the acceptable limit and 400 absolute max.

I usually have to throttle back and limit the climb rate shortly after takeoff to keep it under these numbers. If the engine is already hot, say from a quick land-refuel-takeoff, I have to start throttling back almost immediately after takeoff.

I've been wondering if this is normal or if I need to look into redoing my baffles. Engine is 160 HP O-320 in RV-6A
Click to expand...

Bryan, he said the same thing at OSH 2012.

I like his attitude about CHT. Keep it cool and the engine will last forever. His C-310 engines are at 200% of TBO.

He says at 400 aluminum cylinders are at 50% strength and decreasing as CHT heads up toward Lycomings 500 red line. 400 is the red line in his book, I adopted it some years ago. Pull the throttle back, lower the nose, increase climb speed, increase mixture - do whatever it takes to limit CHT to 400. Yes, it will go up quick after a take off with a heat soaked engine, that is normal. Same rule in my book.

Lycoming says 500 - good advice if your business is selling engines.
 
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DB,

I'm sorry, I don't know you so despite your seemingly authoritative stance on these issues you can't expect folks on this forum to simply "buy it" because you say it. Have you published a study yourself, conducted the testing, what is your education and experience?

Anybody can throw out a limit and sound convincing in doing so. The data and the method used to gather the data is far more credible.

I'm not refuting your 380 number as I don't have the data either, but I do have manufacturers published limits and I do know what they go through to certify those limits and understand the oversight and methods used to test them.
To be clearer..I'm not suggesting operating a lycoming at 500deg is correct because that is their published redline the manual (for O-360 anyway) calls for continuos ops below 430 for longevity.

I've also read the Deakin article posted above many times. It is well written and informative but it is NOT a technical paper.

How are you affiliated with this seminar you propose?
 
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Go to Savvy.com and watch Mike Busch's webinar on proper engine leaning.
If he can get his engines to go 200% past overhaul then I am listening to what he says and not to Lycombing.

John Morgan;)
 
I'm not an engine guy and don't know what problems high CHTs should cause. I do know that my Piper Pacer O-320 had lots of engine problems and I don't know why. It didn't have CHT gauges and I don't know what was happening there. I do know that the engine swallowed exhaust valves twice; both times were at night and in the middle of no-where. I got home OK.

My RV-6 O-360 has good engine instrumentation and I look at that stuff. On the second flight the CHTs were climbing through 450 F and I got on the ground quick.

The engine still runs what would generally be considered on the warm side but I do try to keep it below 430 F or so on climb. Sometimes I throttle back after take off and fly level for a while, especially if it is really warm and a short turnaround. I also climb very rich if it is warm, and it does help a lot. Today it was 110 degrees here; it is a pretty extreme environment. After a while I can almost always keep it below 400 degrees by a bit. In more moderate temperatures it is more like 360 to 380 degrees.

This is way above what most people think is acceptable, but the engine seems to be taking it fine so far. I have put about 1,200 hours on this engine, with no problems at all. The old Pacer would have had to have several cylinder replacements by this time.
 
Popcorn_nommer.gif
 
Go to Savvy.com and watch Mike Busch's webinar on proper engine leaning.
If he can get his engines to go 200% past overhaul then I am listening to what he says and not to Lycombing.

John Morgan
Click to expand...

John, Mike is an advocate and student of the Braly/Atkinson/Deakin folk, and as a result his Savvy business is testiment to the teachings of the science. His results speak for themselves.

Larry, your post, is interesting, it reinforces my new Signature below. Secondly you can do a couple of things, make sure your F/A ratio's are good, the ignition is set up right and fuel flows are good. Make sure you have what George B would call "A conforming engine". Then go work on your baffles and pay particular attention to the air escaping out the front of the engine behind the spinner. Air does not behave as you might like to think.

Ken K
You should be wary of advice....including mine :) But seriously, I think if you do the research yourself you will find my comments are mostly backed up easily from good sources. This stuff dates back to Lindburgh.

I've also read the Deakin article posted above many times. It is well written and informative but it is NOT a technical paper.
Click to expand...

JD's articles are as good as a technical paper, worded for the lay man. Heck this is VAF :D You must not have read my previous post very well, and I say this in all good hearted manner, read the opening paragraphs again.

Folk on here want a one shot answer or a cook book. It is not that simple. You can not just have one recipe, you need to learn to cook to become a great chef. Same here.

How are you affiliated with this seminar you propose?
Click to expand...

This gets me wound up, I understand the "why are you selling me on this" concept, but I have answered it before, and frankly it makes not an ounce of difference if I owned it 100% and made millions from the seminars per year, or just happened to be a student. The facts and data are all that matter. At present I have no interest/affiliation in APS. And if that changes it will not have one ounce of difference whatsoever. APS is basically a "Not for Profit" venture aimed solely at educating pilots into being safer, better educated and saving them money on maintenance and fuel bills. It is not about LOP v ROP or any of the usual arguments about GAMIjectors etc. Truth is they have made a few cents per hour at best, and just cover outgoings, probably costs them thousands a year if they were honest with themselves.

Larry's post above is a good example of why what I propose could in fact save your life. I know folk who have been there......
Hope this helps! :)
 
RV10inOz said:
Here we go again. The same old shots from the hip, like where do you get that from, where is the data....Well there is plenty of data, it supports the case, and it MUST BE REMEMBERED the numbers are not hard 380 +/- 0.005 F
Click to expand...

The request is for supporting data. Please don't avoid the question. Can you supply it or offer a specific reference?

Interesting to note, that while having a debrief session recently with John Deakin, Walter Atkinson and George Braly on the topic of how best to educate, it was noted that to the best of their memory, not one RV owner has flown to ADA OK for an APS seminar. Maybe some have been sneaky and gone in by stealth, but we did discuss why so many Cessna/Beech/Piper owners take the time and spend the money yet the RV community does not. I have my opinion on why, and they seemed to think it was plausible, but none the less an interesting issue.
Click to expand...

Ahh, but we have you.

Larry, your post, is interesting, it reinforces my new Signature below.
Click to expand...

....which appears to violate the VAF "No advertising in signature lines" rule.

APS is basically a "Not for Profit" venture aimed solely at educating pilots into being safer, better educated and saving them money on maintenance and fuel bills.....Truth is they have made a few cents per hour at best, and just cover outgoings, probably costs them thousands a year if they were honest with themselves.
Click to expand...

What a load.

I sincerely admire George, as much for his business skills as his technical knowledge. APS is not something created to fill up his spare time.
 
Hey Jim,

I too have ECI Nickel cylinders and have had higher (than I prefer) CHT's. When my engine was new <50-60 hours, I would see the same temps you are seeing, almost exactly, 420 in climb and 380-390 in cruise.

Ultimately, I did almost everything I could to improve baffling and still my temps were higher (than I prefer). I ended up installing louvers and now even in these unusually hot summer days (105f) I just break 400 in the climb. Usually around 360 in cruise.

I recently noticed that there are a couple of small gaps in my baffling, though small, I suspect they are causing higher temps. I plan to redo my FWD baffles to rectify that. Maybe fixing that will eliminate the need for the louvers.

With some fiddling, I am sure you will get your temps to come down. I also think ECI cylinders just run a little hotter. Keep working on your baffles, checking to make sure that they leave a mark continuously inside the cowl. I would use louvers as a last result.
 
re "The two best investments you can make, by any financial test, an EMS and APS!"

Perhaps it is an indication of an ignorant life in general, but I find these unknown (to me) abbreviations an irritant.

In an attempt to define APS and EMS - an internet search turns up -

Albuquerque Public Schools
American Psychological Scociety
Atlanta Public Schools
etc, etc, etc,

Same with EMS. There are hundreds of Emergency Medical Organization. Nothing related to aviation.

I am not familiar with EMS or APS in context with this discussion. Is it possible not knowing about these organizations, theories, passions or whatever they are, one could be a successful pilot or is one doomed?
 
Supposedly (emphasis) the choke bore on a Lycoming goes flat around 380 degrees and I believe that this is where the 400 degree number came from. Like a lot of old wives tales about choke bores, autogas, LOP, etc. some things never die. The book says 500 redline and thats what it is. Cooler the better.

If your temps are running consistently high its going to be one of these three:

1. Airflow disruptions at the cowl inlets or exits.
2. Too lean in climb.
3. Timing too advanced for the particular compression ratio.
 
thread drift. . .

I guess Ill thread drift. . back to high CHT's

I purchased a 0-360 10:1 electronic ignition rv6a a few years ago. On extended climb the CHT's would go thru 400 pretty easy. I would have to level off, pull the power back, and let things cool down.

One summer day on a heat soaked engine I looked down at only a couple thousand feet and had a cylinder going thru 420 pretty fast. I decided that wasn't acceptable.

After reading some other peoples real world experience I decided to do a little tweaking on the baffles. I added a couple washers to the right rear baffle attachment to get some space there. I used about a tube of RTV on any gap that didn't belong including around the oil cooler. I even added a large fender washer over the cabin heat inlet hole to limit that air being wasted. A little tape over the gap at the front of the cowling top to bottom gap. . .

BIG difference. We've been having 100+ degree days. I can continuous climb at 120kts 1000+fps and be in the 380's on the hottest cylinder..

Little changes can make a big difference.
 
Well, I didn't realise this was such a hot issue.......
Thanks for the replies, specially the practical advice.

I think what I'm getting through all the noise is that my engine won't explode but the long term durability could be affected.

For now, I'm going to make more effort to keep the CHTs down in the climb with operating technique and spend more time on the baffles for a more permanent improvement. Good to hear it can be done.
 
jimgreen said:
Well, I didn't realise this was such a hot issue.......
Thanks for the replies, specially the practical advice.

I think what I'm getting through all the noise is that my engine won't explode but the long term durability could be affected.

For now, I'm going to make more effort to keep the CHTs down in the climb with operating technique and spend more time on the baffles for a more permanent improvement. Good to hear it can be done.
Click to expand...

Pretty much summarizes it.
 
OK, I finally got a call in to ECI.
They consider the Lyc redline of 500 too high.
They like to use a max of 460-475 ( not sure why this is a range and not a hard limit)
Climb temps up to 430 considered quite normal.
Cruise in 380-400 range is fine.( no benefit to operating below this temp)

Asked, if operated in this way is there any impact on durability?
"No, not at all."
By the way the rep responded, sounds like they have been getting some calls on this!
 
Jim

Did you ask if that was based on the old traditional CHT probe (plug ring) or the typical modern day screw in probe?

The rule of thumb is the probe reads 30F less, give or take a bit, so when the old certified machines were built they had the plug type, and those numbers reflect that. This was the industry standard for so long.

You will have the screw in type no doubt, so maybe its worth considering this.

Pressure and temps..... keep the ICP and CHT down for longer life and less costs.

Remember that good mixture control and pilot technique controls the ICP, which in turn affects CHT. However if the pilot controllable factors are good and CHT is higher than expected, it is all about baffles. As was noted a few posts back, little things make a big difference.

As I said in the beginning, I would not accept CHT's as was shown. I would work on solving the issue.

I run my IO540 hard, it is WOT and target EGT leaned in the climb and typically 10-20 LOP or in the flight levels maybe best power, although the fuel savings at FL130 are significant at 10LOP. Down Low, it is WOT, and 60-80 LOP.

My CHT's are rarely over 370, so if I live in a hot place and run hard, with good CHT's, and you do not replicate this, you are leaving money on the table so to speak. You invested so much money in your pride and joy, why not aim for perfection rather than accepting third rate.

I hope that makes sense and does not offend anyone, but if it does perhaps the message is aimed at you.

Here are two examples, the first is blurry so ere are the details, 1000' on a high QNH day and the RV generates a bit extra MP so 29.6" and 2430 RPM, 52LPH and generating around 79% power, 60-80 LOP. Check out those CHT's :D
photo2-3.jpg


Next is in the cruise at 9000' and WOT and LOP with a fuel flow giving 63% power, and again look at those CHT's.;)
photo3-1.jpg



By the way, from that position you can dive hard to the airport, you can't shock cool a cylinder that is already cool ......... hehehehe
 
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