Wet Heads

[Lumps]

The following is from a Mooney M20M TLS flight evaluation.

It seems that perhaps due to 'aggressive leaning' to the 1750°F TIT limit the original TIO-540-AF1A often couldn't get passed 3-400 hours without cylinder work, but Lycoming installed oil-cooled valve guides, called it the TIO-540-AF1B and.. I don't know, was this the end of the problems? Also, if it was such a problem with this engine why don't Chieftans etc also have wet heads, the article seems to indicate not. The fix was specific to the Mooney and had been also used on the Beech Duke before.

It seems like they set a very high TIT limit, told pilots to lean to it in their POH and then had to introduce an engineering solution for a problem they sort of created themselves. Seems like it would have been easier to reduce the TIT limit at high power settings.

And fast it is. The engine is a version of Lycoming’s parallel-valve; 540-cubic-inch opposed six with a single AiResearch Turbocharger and carries a maximum power rating of 38 inches manifold pressure and 2575 RPM. Two controllers operate the single wastegate to regulate pressuri ze d air to the induction system. With this system, the engine is capable of maintaining its full 270 hp up to FL210 under standard conditions. With this high 21,000-foot critical altitude, the TLS is able to achieve very high cruise airspeeds. At FL250, as high as you can legally fly in the M20M, it’s still possible to utili ze maximum continuous power – 34” and 2400 RPM, which is about 240 hp or 89%!

Of course all this speed comes at a cost - about 18 gallons of Avgas per hour of cost to be specific. And that is if you lean aggressively to the 1750-degrees-Fahrenheit turbine-inlet temperature (TIT) maximum, one of the highest certified TIT's in piston aircraft. We will discuss leaning in detail again later in this report.

One thing did become evident during the first few years of production. With the airplane delivering such high cruise airspeeds, at high altitude with high power settings, many TLS owners discovered that their airplanes needed engine work at 400 to 500 hours.

In retrospect, this could be a predictable situation. Here we have a large-bore engine producing 270-horsepower and in the hanger next door may be another variation of the TIO-540 in, say a Navajo Chieftain, producing 350-horsepower. It would be easy for the average TLS operator to think his engine was a de-rated version of the 350-hp monster. At 270 hp it’s not working as hard as the engine in the Piper, and using nearly 90% of that number for cruise should pose no major problems. Unfortunately, this premise is incorrect. The two engines have little in common. The engine used in the TLS is rated at 260 hp without the turbocharger – at a higher compression ratio and RPM – and is really a lightweight version of the Navajo’s 540. As a result, exhaust valve guides bore the brunt of the wear from these operations.

There was a predictable rise in oil consumption and dropping compression readings during as little as 300 hours of operation. Fortunately, these excessive wear indicators did not lead to any catastrophic failures. But many owners discovered that a quarter of the way to overhaul, top-end engine work was necessary. One of the factors in this increased need for unexpected maintenance could have been the high TIT red line. Most turbocharged Lycoming engines of that day had a more conservative limit of 1650 degrees F, and they had a better maintenance picture than the early TLS’s.

Mooney and Lycoming came up with a solution for the TLS top-end wear problems. A process that Lycoming used successfully to cure similar problems on the TIO-541 Beech Duke engines – oil cooled exhaust valve guides – was accomplished on the TLS. The illustrative name “wet head” was given to the conversion that was accomplished on all production engines that resulted in a designation change to TIO-540-AF1B. The change from the AF1A to the AF1B brought about the nickname for the engine, the “Bravo mod”, and in fact the TLS became the TLSBravo and has since been shortened to just the Mooney Bravo.

In this conversion (and on subsequent production engines) oil is fed under pressure to a gallery in each cylinder head adjacent to the exhaust-valve guide. The guide it self has a small groove cut into the outer diameter allowing oil flow to surround the guide and draw away heat. From the valve guide, this additional oil flow is routed through the rocker boxes where it helps to draw away additional heat and then through the normal drains back to the sump. The modification is easily seen as a bunch of snaking external oil lines leading to each cylinder head. Our information is that all US airplanes have been modified (Mooney paid a substantial part of the Service Bulletin), however some foreign TLS’s may have been missed.


Full report: M20M Evaluation (http://www.mooneypilots.com/mapalog/M20M%20Evaluation/m20m_eval.html)

[Old Akro]

Walter Adamson & John Deakins have spoken eloquently about TIT limits in recent threads. You should seek that out. It may be in my thread on leaning the TSIO 360

[Jabawocky]

Atkinson that is ;)

I should also point out that agressive leaning is the wrong phrase to use. It should be called abusive leaning. Agressive leaning would be on the far LOP side of peak EGT/TIT and would result in far lower cylinder pressures and CHT's.

The problem is also found in the new Turbo 206's where in flight failures have occurred here in Australia. One of this countries beter engine shops has had them in for rebuild. Their comment was also about valve guides and Dukes :hmm:.

Be it poor design or not, with "abusive leaning" on the rich side of peak EGT, and modern glass panels alowing accurate levels of abuse, then the cylinder pressures and thus temperatures become a problem far sooner or far more often than they otherwise would.

The TIT limit is not the actual problem, so correlation of the two is not correct. For example you could create a very high TIT and have much lower ICP and CHT by retarding the spark timing. In doing so you could have kinder load on the cylinders but be at the TIT limit.

The TIT limit is a point where the turbine can operate all day and not suffer from creep problems temp & RPM), it is permissible to exceed it for short periods to establish peak and even then the time frame is generous. TAT have deliberately had to retard timing to do extended TIT testing for FAA certification projects and despite such treatment they live happily. Tough little critters!

TIT is being used to measure a point along a curve, and the famous set of curves by Advanced Pilot Seminars is worth noting with respect to the EGT/TIT relationship to both power and CHT. Study this for a while to get the concept.

http://i849.photobucket.com/albums/ab58/jaba430/Landmarksgraph_zpsbfb07cbb.gif

As for the POH, I have not read that particular one, and if you wish to send me a copy I would happily study it for comment, but it is likely to follow in the footsteps of so many pathetically and scientifically wrong POH's of the past. (Not opinion, just sad fact).

[Lumps]

Akro - I've been reading that thread, very educational but I thought this may be thread drift so started another.

So is the wet head a standard TIO thing these days or was it specific to Mooneys and Dukes? Why was this problem only showing itself on a seemingly de-rated 540?

I understand TIT temps are arbitrary when talking about mixture settings, but you'd have to assume seeing as it is a Lycoming that they'd be recommending ROP operations in a turbocharged engine at FL's that were probably not rich enough, hence the high TIT's on the wrong side of Jabawocky's graph, high ICPs etc.

This sought of ties into another question I have, why did the Piper Malibu get discontinued? Apart from the fact that the then TCM had to pay out US$32m to a pilot injured in an engine failure related incident (wikipedia) what was the real weakness of the TSIO-520BE. If anything it should have been a more reliable engine than the TIO-540 that replaced it, as it was meant to be run LOP only. Sort of flies in the face of the science.

[Jabawocky]

The weakness of the TSIO 520 was the fact despite it being mandatory to run them LOP they were not. This was most likely the poor education at the time but the old habits and some high profile media articles of the day describing how it performed better at something like 50 ROP, and poorly tuned injectors.....problems a plenty.

If John Deakin or Walter Atkinson see this thread they will surely give a much more accurate history lesson as they lived right through it.

As for the Lycoming problems, it is worth a chat with the folk at Brisbane Aero. ;)

[Old Akro]

Atkinson that is

I'm sorry. I was passenger in a car on the iphone. Combine that with Apple auto correct and anything can happen!

[Old Akro]

Why was this problem only showing itself on a seemingly de-rated 540?

I wonder if this is pointing to a cylinder cooling issue more than a combustion condition issue. I wonder if cowl flap technique might be involved??

Also, I wonder if baffle condition might be an issue. It seems to me that baffle condition doesn't get due attention from many Australian LAME's.

[dubbleyew eight]

baffle condition is critical to the longevity of your engine. ....but what would I know :E

I just drink the occasional scotch and fly an old engine...

[Jack Ranga]

I was going to report this thread when I saw the title (for being rascialist)

[Old Akro]

I just drink the occasional scotch and fly an old engine...

Wheras I drink the old scotch and fly an occasional engine...:ok:;)

:E

[sms777]

Hey Jack!.....I think you are referring to towel heads...:oh:. Oops.....here we go again . I got banned for being a racialist once . I could not understand why since I hate everyone equally....Try not to hijack the thread but welcome back.....
What was the thread about again?.......

[Lumps]

So pilots incorrectly assumed they could run this engine hard because after all it's 'only a derated Chieftan engine' and As a result, exhaust valve guides bore the brunt of the wear from these operations.

This seems to me a non-sequitur.

It's indeed a mystery, wish there were more engine builders scouring forums on a Sunday!

[Jack Ranga]

777, if you know me you know I STAY on topic :ugh:

There's no room for rascialist stuff on bulletin boards :cool:

Back to it: wetheads

[jdeakin]

Jaba said:
If John Deakin or Walter Atkinson see this thread they will surely give a much more accurate history lesson as they lived right through it.
"Lived through it?" <Harumph> First we lived through the extinction of the dinosaurs, then we saw the creation of all that oil, then we saw airplanes come along, then there was the Malibu - and then there wasn't.

(That's called humor, er humour! You may laugh now.)

The weakness of the TSIO 520 was the fact despite it being mandatory to run them LOP they were not.That deserves a repeat! The LIMITATIONs section of the POH clearly stated that LOP operations were MANDATORY, and ROP operations were forbidden!

This was most likely the poor education at the time but the old habits and some high profile media articles of the day describing how it performed better at something like 50 ROP, and poorly tuned injectors.....problems a plenty.Yes. It was customary in those days for FLYING MAGAZINE to publish articles in almost every issue with a pilot report on the "Airplane of the Month." Pilots all over would paste these articles on hangar walls, and discuss them, and use them to sometimes buy their airplanes. Good idea, but often poorly executed, often by the Editor.

So, they did the usual thing on the Malibu, a lovely airplane, if a little bit cramped for the tall pilot. He took it out, and reported that they set up cruise power at LOP, as per the LIMITATIONS section. He further reported that the airplane met the factory specifications for performance, and listed all the parameters. So far, so good.

Now, you've got to realize, in those days (and in certain circles these days), "Leaner is worse, Richer is better." Leaning into the LOP range was quite a leap, unknown, unfamiliar territory, and it was somewhat controversial.

Then, as an offhand, unthinking comment, he said that the engine was just a little bit rough at that setting, but this could be corrected by enriching the mixture just a little. No details, just push that li'l ole red knob in a bit. That would, to his mind, made the mixture "better" and smooth the engine out.

That one offhand remark was wholly responsible for many Malibu engine failures, accidents, and deaths. What no one knew (then) was that the LOP setting was critical, and that LEANER would have been better (but rougher), and RICHER was moving squarely into the APS "Red Box!"

And there, my friends, is the classic example of engine abuse by the ignorant. You must, must, must, at about 60 to 65% power and above, operate RICH ENOUGH, or LEAN ENOUGH. To get LEAN enough, you must have good FUEL DISTRIBUTION TO THE COMBUSTION EVENT, and the ignition system has to be in very good condition. If those conditions are not met, you are doomed to operate ROP, where things can be, and usually are, far more sloppy.

(A footnote to this. The Malibu (and a few others) have Inconel rotors in the superchargers, which allow TITs of 1750℉/955℃. The TURBOS are happy all day long at 1750, and these TITs may be exceeded for a short time (a couple of minutes) for finding peak and other tests. But a few (most) airplane manufacturers chose the cheap route in supplying exhaust PIPES that were too thin, or not good material, and many of them failed prematurely after running for many hours, giving the Turbo or the TIT limit a bad reputation.)

(A bad reputation like the Pit Bulls of today, and the T-Rex of yesteryear. I used to raise T-Rex's, and as long as you kept 'em fed they were very gentle. They preferred virgins, which was a problem around Walter, who had other uses for them, and who raised Diplodocus's. Why, I remember the time...but that's a story for another day.)

Best...
John Deakin

[Jack Ranga]

(That's called humor, er humour! You may laugh now.)

Ban him :ugh:

[Jabawocky]

Ohhh Deakin....you are a funny man. My eyes are watering once again.

But for those learning something, stop laughing at the humour and study Johns words VERY carefully.

And as for Atkinson and the virgins.......I think he appreciated the Virgin Australia Premium Economy. :ok: :}

[Jack Ranga]

He deserves no less ya tightarse! Why wasn't he in business?

[Jabawocky]

ssshhhhh just coz John is a tights airline guy...and Walter thought it was Business ;)

Hey Bro, be in LAX when I am as JD and I are doing lunch. I am sure you and he would have fun catching up again. :ok:

[Jack Ranga]

and Walter thought it was Business

lol :D

Dates?

[Jabawocky]

Lumps,

If you need some more "one on one" attention you should be able to email me via the APS website.

Hope this has helped.:ok:

[Lumps]

Thanks Jabawocky, I don't own a Mooney M20M, was just a hangar talk curiosity thing. Here is the POH excerpt - they allow max continuous power (89%) at peak TIT. Red box be damned it seems.

http://www.flyingwarbirds.com.au/wp-content/uploads/2014/06/Screenshot-2014-06-09-15.31.591.png

[A Squared]

Also, if it was such a problem with this engine why don't Chieftans etc also have wet heads, the article seems to indicate not.

Nobody seems to have responded to this particular part of your question, so I'll have a shot at it:

The TLS engine is unlike the Navajo engine, the TLS engine is a "parallel valve" engine, and the Navajo engine is an "Angle valve" engine. The parallel valve engines are much lighter, and have significantly different cylinder heads. The angle valve cylinder heads have better cooling at the valves; the valve guides are longer (more transfer area) the valves are further apart so have more mass between them to transfer heat, and have greater cooling fin area. So, with a different head construction, different compression ratios and different operating parameters, it doesn't follow that the Navajo engine should need oil cooled valve guides like the TLS engine does.

[Jabawocky]

AxA, good pickup. I had forgotten that was even raised.

And Lumps, you hit the neail on the head. The use of the expression "best power" is not necessarly "Best" as in "The best" spot to operate. A concept lost on many folk.

Just for your entertainment and educational pleasure, and for any of your hangar flying mates, go to the website and play this interactive "Red Box" demo, and then you can manipulate the one at the bottom of the page.

Another free give away courtesy of Advanced Pilot Seminars. Advanced Pilot (http://www.advancedpilot.com/redbox.html)

And we must thank Noel and Felicity Schultz at Chinta Air in South Australia for asking us to put that n the website.:ok: Of course it could have been the effects of Felicity and her over zealous force feeding some of us red grape juice......but thats another story best left alone, because I bet she is watching this :}

[Lumps]

Asqrd thank you! At last

Running 89% power at peak TIT with the lowered heat transfer ability in the FLs probably didn't help CHTs either.

Jaba - the M20M POH comes under fire by one of the engineering test pilots that helped write it - the article is in a certain folder under 'cooling down turbos' you might recognise it!

[Old Akro]

Red box be damned it seems.

Walter, John & Jaba all contributed generously to my thread about the TSIO 360. Peak TIT is not necessarily in the "red box".

You should also note that TIT is a different curve than peak EGT. TIT peaks later than EGT, so peak TIT will almost certainly be LOP EGT.

An interesting question for Walter et al. is: If below 65% power is about the threshold safetly go LOP - or just about any other mixture condition - in a de-reated engine such as this, is the 65% taken from the original power rating or the derated power rating?

[Jabawocky]

Akro, I am not sure I can agree with the different curve bit, the TIT is always a higher number but as for lagging significantly behind relative to fuel flow left to right, not so much. The TIT is directly related to all 6 inputs, and is a collector average.

You do raise an excellent point however about what do you consider the base line for 100%. In a derated engine say the 235HP in the C182, this is achieved by nobbling the RPM, thus you start out at 90% of the original 260HP engine and the ICPs are the real number to look at. They are actually higher per cycle but with fewer cycles per minute there is less HP.

Remember the red box concept has fuzzy edges and is conservative.

So the Parallel Valve turbo engine is more closely related to say the IO540D4A5 Comanche engine, except that the CR is 8:1 midway between the 8.5:1 of standard CR's and the Turbo's normally 7.2/3:1 in many planes. So I would not view this as a derated engine at all.

So to get a rough guess on this I would say all the variables are about even. The buffer of the fuzzy edges of the red box will cover it.

The point here to remember the Red Box is actually based on a nominal cylinder pressure limit that the Three Amigo's determined was a good safe number to use that would give longevity and some wriggle room for the variations you are talking about. You are trying to split hairs but in reality we just need to be within a few cm of the deal. If that makes sense.

Add to that the conservative nature the ICP boundary for the red box is in the order of maybe 5-10% in terms of ICP. So you could push the edges in a bit, but when you do the longevity is compromised if all other things are not optimal, namely cooling airflow distribution.

So in a non exact science answer what would I call the TIO540AF1A relative to the red box? I would call 270=100% but no room for squeezing the edges as much as say the IO540D4A5.

One thing we show in the class is how the edges of the red box were defined during its development. Almost impossible to describe here in a post as you need graphics moving on a screen, but there is a science behind it.

Hope that helps and if JD or Walter have any tidying up to do, I am sure they will give me a quick http://www.beechtalk.com/forums/images/smilies/beechslap.gif

[Old Akro]

Akro, I am not sure I can agree with the different curve bit, the TIT is always a higher number but as for lagging significantly behind relative to fuel flow left to right, not so much.

I've had a fair bit of trouble getting real data on this. There is a bit in the Bosch Automotive handbook and I've found a couple of old NASA papers. But none of it is definitive. For engine calibrators & researchers, TIT and EGT are crude measures. Its only pilots who are stuck trying to operate with them!

We should really be moving toward installing lambda gauges. Then we could measure the A/F ratio rather than use EGT as a proxy for it. If I had an experimental aircraft that's what I'd do. For my certified twin, I'd rather have a go at reconciling the Russians & Chinese than go through the STC process.

TIT is higher than EGT because is a more constant flow of hot air. The EGT probe is allowed a fraction of cooling in between pulses It measures temperature a bit like measuring RMS AC voltage.

TIT appears to peak 25 - 50 degF after EGT. But I'm not sure why. I can imagine that the temperature in the exhaust pipe would be a complex thing that behaves differently ROP & LOP and at different gas temperatures & flow rates. Some ROP conditions will have continued burning of the charge in the exhaust piper for example.

I believe the TIT curve will be a bit "flatter"and less "peaky"than EGT. But its at the margin really.

Which is an opening to talk about gauges. A stock analogue gauge using a k type thermocouple is lucky to be with 100degF and its calibration curve will be non-linear. I calibrated our stock Alcor ones and they are within about 10 degF in the operating range after fettling, but outside that it very quickly deteriorates. The digital gauges are a lot better, but not all are cold junction compensated and I challenge you to discover which are! Without cold junction compensation they can vary by the change in ambient temperature from the calibration temperature - in other words up to probably 50 degF. The trends count more than the absolute readings.

This impinges on the TIT debate. There is no point in being hung about about being degree perfect on an instrument that will probably have 50 degF error.

I think manufacturers install TIT gauges to protect the turbo, then they get used as a proxy for EGT for the purpose of leaning. The proper thing is to install an engine analyser and use EGT for leaning and the TIT to monitor turbine temperatures to protect the impeller & housing.

[Lumps]

Peak TIT is not necessarily in the "red box".

Quite. But to put it back in context:

Running 89% power at peak TIT

What you say about TIT peaking 25-50dF after EGT is interesting though, could it be that the clever heads at Mooney meant the engine to be run LOP!?

(I'd say there'd still be a few pots with uncomfortably high ICPs, at 89% power on a factory engine)

[Jabawocky]

Howdy Akro,

I have been studying some dyno runs to see if I can spot what you are talking about and I can't, and it does not make sense in a conforming engine.

You say the TIT will be flatter at the top, yes that makes perfect sense as some start peaking and falling the others are depending on the close F/A ratio matching going to peak at different times, so there will be some individual EGT's dropping while others are still rising.

I am sure you have a good grip on that, so I really do not see a mathematical average differing greatly from what the collector average (TIT) is measuring actually happening. The trend graphs on the GAMI dyno all track each other, accurately and even on an engine with unusual exhaust plumbing.

I think we are looking for microns when measuring for cm's here.

If on the other hand you had an engine with vast spreads of F/A ratio's then I can see a measurable effect, but that would not be a conforming engine would it?

JD or WA might have some views to add when they wake up over there.

[Walter Atkinson]

Jabba has it correct.

TIT and EGT track very closely in a conforming engine. Based on our evaluations, the raw values of the EGT/TIT probes are quite close to reality. The TIT probe sees six pulses of hot gas instead of one as in EGT every 720 degrees of crank rotation. In MOST applications, this results in TIT being a higher value than EGT--even though the gases are actually cooler at the TIT probe since it is further down the plumbing. There are a few installations where TIT is lower--like the C-421.

[Old Akro]

Walter, thanks.

I don't have primary data like you. So, I'll defer to your advice.

My belief that EGT & TIT curves is part based on a conversation I had with a mate who is an ex FEV engine calibrator and some old NASA papers. His hand drawn graphs are still on my office whiteboard.

I haven't looked back in detail, but one of the NASA papers I liked best was titled " ultra lean combustion in aviation piston engines" by a guy named Chirivella. His TIT curves are a bit different from his tabled EGT curves. The peak is less defined and the slope up to peak less steep.

There was truly some amazing work done by NASA, the AIAA and a couple of the universities in the sixties & seventies. Its a pity it didn't filter through more. I'm astounded and grateful that NASA gives full & free access to it all via the Langley library. One of my favorites (and please don't ask me to find it) is a project done by a university who designed and installed a new wing on a Seneca using a laminar airfoil, full span flaps and spoilers for roll control. But that's a diversion.

I forget why I think TIT peaks about 25 degF after EGT. Chirivella does not put EGT & TIT on the same graphs. I may have transposed one to the other using BMEP as a reference. I also fancied John Deakin may have referred to this in the thread on leaning by reference to TIT in BeechTalk. But, I don't recall clearly.

[Jabawocky]

Akro,

I can only imagine the hand drawn curves are possibly accurate, and if drawn on a whiteboard by me, possibly not :ouch:, but in any case the flatter peak etc on any given day would be as a result of variation from cylinder to cylinder.

I have rerun some dyno runs which are clearly showing no offset. That is not to say you can't have some as I suggested above from a larger GAMI spread, or other external influences but really we are measuring microns when cm would do I think.

If you can find something on this that we can all learn from it might make for intellectual entertainment but from a piloting perspective it may not be significant. But the more I know the more I realise how much more there is to know.

JD said he had nothing to add by the way. He has a word quota per day I think. Some would say I should have one and a lot smaller too :}

[jdeakin]

Jaba said:
JD said he had nothing to add by the way. He has a word quota per day I think. Some would say I should have one and a lot smaller too :}Naw, just lazy. I figure if someone says pretty much what I'd say, leave it alone.

Best...
John Deakin

[Old Akro]

I have rerun some dyno runs which are clearly showing no offset. That is not to say you can't have some as I suggested above from a larger GAMI spread, or other external influences but really we are measuring microns when cm would do I think.

Walters comment about "conforming engines" may be the missing link.

[Jabawocky]

Akro..... :uhoh:

That was my post not Walters, but anyway what missing link?

Either of us...or JD whoever gets to it first, will most likely answer you, but I don't get it. :confused:

I mentioned about the conforming engines. But still do not follow you.

Howdy Akro,

I have been studying some dyno runs to see if I can spot what you are talking about and I can't, and it does not make sense in a conforming engine.

You say the TIT will be flatter at the top, yes that makes perfect sense as some start peaking and falling the others are depending on the close F/A ratio matching going to peak at different times, so there will be some individual EGT's dropping while others are still rising.

I am sure you have a good grip on that, so I really do not see a mathematical average differing greatly from what the collector average (TIT) is measuring actually happening. The trend graphs on the GAMI dyno all track each other, accurately and even on an engine with unusual exhaust plumbing.

I think we are looking for microns when measuring for cm's here.

If on the other hand you had an engine with vast spreads of F/A ratio's then I can see a measurable effect, but that would not be a conforming engine would it?

[Lumps]

From an article written in 1998:

Current owners of wet-head TLSs and potential customers for the Bravo might be asking the same question: Does the oil-cooling scheme make the turbo Lycoming worthy of its 2,000-hour TBO? Too early to tell, but the initial indications are promising. The question remaining to be answered is this: Now that the exhaust valve guides are cooler, what is the next-weakest link in the chain? Bravo (and wet-head TLS) owners then face a dilemma square-on: Do you throttle back a bit--to, say, 75 percent of maximum for cruise--and sacrifice about 10 knots for the possibility of greater engine longevity? Or, do you run at maximum cruise--because, as one TLS owner told me, "I didn't buy the airplane to go slow"--and hope the additional oil cooling does the trick?

Would love to know from any Mooney drivers or maintainers if this engine proved capable of such abuse with the addition of wet heads.

From a Mooney test pilot:

With all that said and considered, this former test pilot flies turbocharged Mooneys at 50 degrees rich of peak TIT. Like the normally aspirated Mooneys, it is my professional opinion that this mixture setting is a perfect compromise between best power (100 degrees rich of peak) and best economy (peak) mixture settings. I have never seen an engine over-temp in level cruise using 50 degrees rich of peak, even the notoriously hot running -GB engines in the early 231's. I might be using a little more fuel at 50 degrees rich of peak TIT than at actual peak, but come on-- what's an extra gallon an hour of burn cost compared to that $60,000 engine I'm flying behind? Saving a few dollars of extra fuel burn by operating at peak TIT or even lean of peak TIT turbocharged engine just isn't worth it to me. Replacing a turbocharged engine costs too much.

[Walter Atkinson]

1) the oil-cooled valves do have good service records.

2) It's a shame that that Mooney "test pilot" knows so little about the laws of physics or engine management. His statements are simply at odds with the laws of physics or the known data.

[Jabawocky]

Hey Walter...ya think that bloke might have written a certain Lycoming publication? :}

amazing!

[Walter Atkinson]

***ya think that bloke might have written a certain Lycoming publication? ***

Little chance. The Mooney guy is at least a pilot.