MP and TIT for upgraded turbo/intercooled K Models

[Red Leader]

Hello guys! Having recently purchased a Mooney, I have found lots of useful information in this forum so I am hoping I can tap some of the expert knowledge here to help me address an issue. My purchase is a 1981 M20K with an added Intercooler and Merlyn variable wastegate. The POH numbers for my plane do not reflect the MP for the upgraded engine performance. My instructor (Insurance checkout), although very helpful, had me keeping the pressure very low and expressed great concern about over-boosting the engine - I am assuming that is still possible even with these upgrades? My TIT gauge was inoperative so my field mechanic replaced it with a known good unit but it still isn't working so my questions are two-fold.

1) Where can I get an accurate MP/RPM guide so I can fly my plane with these upgrades at more mooney-like speeds?

2) Until I get the TIT repaired, I am treating my CHT gauge like a TIT gauge, so I keep the temps around 5k or less. Is that a fair use of the CHT gauge?

I am currently flying just about full rich and running 2350rpm and 23". Not blistering performance but until I get the last part working properly, I am concerned about over-boosting/overheating the turbo. My hottest CHT never exceeds 380. How much manifold pressure is too much? Any advice? 

[LANCECASPER]

@NewOldPilot

This is the Operation Equipment List from a '97 M20K Encore that I used to own. Your POH has a page just like this. It will show that even on day VFR flights you are requited to have a functional TIT gauge to operate the airplane. I also used to own a 1983 M20K 231. A faulty TIT gauge grounds the airplane. Even though that may sound like bad news, it's not. You do not want to operate this engine in particular without all of the gauges, especially the TIT gauge with a good, known, tested TIT probe. 

[231LV]

Agreed. You cannot legally fly the plane without an approved TIT. I have a JPI 900 which incorporates an approved TIT and an entire engine management system including RPM and MP. The Intercooler and Merlyn is about the best combo for the 231 but requires engine management...especially with the Merlyn. I typically don't fly with more than 28 inches of MP.  The intercooler essentially provides a more efficient boost by cooling the air so you must reduce your MP to compensate. I am surprised a certified flight instructor even flew without a TIT but he was correct to be concerned about overboost. I fly LOP and find my hottest CHT's in the low 300's unless I am up high where the turbo is working hard. Usually set up 2500 rpm and run about 9 gph. Up high, that trues out at about 175kts. I recently put a vernier throttle in which makes managing the Merlyn much easier.

 

[stevesm20b]

I have a 231 with the turbo plus intercooler and the merlyn wastegate. I use the 252 manifold and rpm limits. I run 36 inches and 2700 rpm for take off and climb, full rich. For max cruise I run 28 inches and 2500 rpm. The max TIT is 1650 but I don't like to run it that high. I lean for about 1550 to 1575 which is about 12.5 gal per hr. At 2500 rpm and 25 inches I can lean to peak TIT and be under 1550 TIT and burning about 10.5 gal per hr. I have the TSIO 360 GB engine which tends to run a little hotter than the LB engine. At high power settings without a TIT gauge you run the risk of overheating the turbo even when the cylinder head temp is under 400 degrees.

[Red Leader]

Thats great advice, thanks for the information. My 231 is currently in the shop having the TIT fixed so I hope to be flying it soon. The pressures and RPMs being run by similar airplanes seem to differ between models or pilots. I will get a better idea how to dial it in once that last item is fixed. I misspoke about using my CHT gauge as a TIT gauge - I meant to say I was using my EGT gauge as a TIT gauge, thinking they would be very similar. Soon to be resolved - thanks again for your knowledge!

[LANCECASPER]

20 hours ago, NewOldPilot said:

Thats great advice, thanks for the information. My 231 is currently in the shop having the TIT fixed so I hope to be flying it soon. The pressures and RPMs being run by similar airplanes seem to differ between models or pilots. I will get a better idea how to dial it in once that last item is fixed. I misspoke about using my CHT gauge as a TIT gauge - I meant to say I was using my EGT gauge as a TIT gauge, thinking they would be very similar. Soon to be resolved - thanks again for your knowledge!

TIT will always be considerably hotter than EGT. You are accumulating the exhaust from 6 cylinders at the inlet of the turbo.

If the TIT probe is older put in a new probe or your reading will be too low. If the airplane was purchased with an inop TIT gauge and it was flown like that, have someone carefully scrutinize the exhaust system and especially the clamps that attach to both sides of the turbo. Having one of those fail may not ruin the engine, but it stands a really good chance of killing you and everyone else in the cabin. That firewall only lasts a few seconds with a 1600 degree blast furnace pointing at it.

[spistora]

If you have the Turboplus intercooler, they have  power correction chart near the bottom of their webpage: http://www.turboplus.com/mooney231-intercooler.asp

http://www.turboplus.com/documents/Turboplus-power-correction-table.pdf

[kortopates]

The aftercooller, nor Merlyn, changes the power settings. The way this STC works, and I'll use Turbo Plus as an example, they provide a chart to modify your MAP setting based on the amount of cooling your getting rom the aftercooler. They suppose to include a differential temperture gauge when installed, measuring the difference CDT and IAT - the difference being the amount of cooling your getting. Based on ths differnence which equates to na incease in air density you need to reduce the POH MAP by that amount specified in their table. 

You can get the table at the Turbo Plus website here along with additional documentation (if you have the Turbo plus installation - its the most common): http://turboplus.com/documents/Turboplus-power-correction-table.pdf

I've found 30-35C typical amount of cooling, and based on that you can see that 40" uncooled MAP is equal to 37.5" cooled. So your redline MAP setting is nominally reduced from 40" to 37.5. RPM doesn't change. So for any performance chart in your POH, you can simply take the specified MAP setting and reduce the MAP per the chart. But when you look at the table for power settings at 30" and below, you see for the amount of cooling we've been using that a 2" reduction in MAP from the POH is all you need.

I am sure you can get the differential temp gauge from Turbo plus if you need it.  

Or you can also be even more conservative and go by the 252 numbers. But that engine has an entirely different induction system and turbo system. But using only 36", as used in the 252, is a good conservative safe number as well.

The biggest problem with these engines is that the max FF isn't set up based on new redline ~37.5" inches, in that the mechanic still set it up at 40" which results in the engine is not getting enough fuel at takeoff pushing TIT's above 1450F at redline (37.5") which  is much too high. 

Lastly TIT is usually 100F > the EGT on the JPI monitors.

Welcome to Mooneyspace and the Mooney ownership community.

Edited February 2, 2022 by kortopates

[carusoam]

On 1/31/2022 at 8:18 PM, NewOldPilot said:

 

2) Until I get the TIT repaired, I am treating my CHT gauge like a TIT gauge, so I keep the temps around 5k or less. Is that a fair use of the CHT gauge?

 

I’m glad you thought to ask these questions…

Transition Training is a great way to get up to speed with everything you want to know…

 

Specifically…

I liked the number 2 question the most…

EGTs and CHTs are loosely connected…

And EGTs are loosely connected to TITs…

 

But, for the safety of the turbo’s health…

none of the CHT or EGTs can tell you what the TIT would actually be reading….

EGTs are highly dependent on location in an open ended tube… (nice to know about their sensitivity to everything)

EGTs are averaged over time… one flame front per two revolutions…

TITs are seeing six flame fronts in the same amount of time…. (Really affects the average temp that the gauge is reading)

Chts are on the cold side of the engine, and have very little in common with temps inside the hot side…

 

Now for the hard part…

You know there is a minimum equipment list right?

This list is in the POH… for your specific plane…

See if the TIT gauge is listed as a must have for day, night, VFR, or IFR flight…

For NA Mooneys… a single CHT is required but an EGT is not….

For TC’d Mooneys… if I owned the plane the TIT would be a requirement…

It is too easy to overheat the exhaust system of a TC’d engine…. Care should be taken to avoid the damage that gets caused by excessive wear… caused by extra heat….

Kind of a heads up and what to look for during your transition training…

At least find the MEL in the POH and see if the TIT is required for flight…

PP thoughts only, not a CFII…

-a-

 

[81X]

You should have a supplement with the intercooler. I believe the only two intercooler for the 231 are the airflow systems and the turbo plus. Do you know which one you have?  
 

Basically  there are two ways to operate this- the easy, conservative way or the harder, calculated way. As others mentioned, the 252 power charts are the easy way- 36” 2700rpm to cruise and then max cruise 28” and 2500RPM. Yields good performance and good heat management in most conditions.  The harder way is to use the power charts and intercooler corrections to take into account OAT and altitude. 

Engine heat is the enemy of the 231.  Keep your TIT in the approved range, all CHTs generally below 380, power set reasonably, and you’re generally ok  

Feel free to PM me as I’m a 1985 231 owner with the same engine mods and can talk through how I operate. It’s a great airplane!! 

[carusoam]

We have the turboplus guy around here if you have their intercooler…

-a-

[Red Leader]

Looking for the Intercooler info - shop has the books and my TIT should be repaired shortly. Thanks for all the information, you guys are super helpful!

-R

[carusoam]

1 hour ago, NewOldPilot said:

Looking for the Intercooler info - shop has the books and my TIT should be repaired shortly. Thanks for all the information, you guys are super helpful!

-R

Do you have a turbo plus?

let’s invite @Turboplus to stop by…

-a-

[Red Leader]

My shop has the books so I don't know which Intercooler is currently installed but I do have the Merlyn wastgate. My dash has a readout to determine temperature differential so I know how much power to reduce based on the difference between the two temp readings. Is that device on any intercooled airplane or just ones with the turbo plus Intercooler?

[carusoam]

Having an intercooler…

opens up a whole bunch of power…

having instrumentation, allows you to use it safely…

or know when something needs attention…

 

When an engine decides to have pre-ignition…. You may have only a few minutes to do something different…

Get the docs, have the instruments, know everything is working properly…

The cool thing about modern planes… the POH data is meaningful…

The ugly thing about pre-ignition… piston crowns are easily melted…

PP thoughts only…

-a-

[kortopates]

15 hours ago, NewOldPilot said:

Is that device on any intercooled airplane or just ones with the turbo plus Intercooler?

Its just on STC'd aftercoolers such as used on the 231 and few other aircraft like the Turbo Arrow and Turbo Seneca. Complete factory turbo  engine certiifed with hydraulic wastegates and aftercoolers like the M20K 252 don't need this added complication nor do they that have the IAT limit you have the 231 because the aftercooler guarantees its not an issue.  Plus the hydraulic wastegates are fully automatic, unlike the pnuematic Merlyn, and allow you push the throttle fully in, without overboosting, and MAP doesn't change with altitude. Greatly simplifies engine operation. 

[Will.iam]

16 hours ago, carusoam said:

Do you have a turbo plus?

let’s invite @Turboplus to stop by…

-a-

I thought the turbo plus has the side scoop on the right side of the cowl like the 252 does for air intake but is dedicated to flowing over the intercooler where as the other aftermarket coolers do not modify the cowl for the air flow over their intercooler. I. E. Might be easier for the OP if he remembers seeing a naca opening on the right side cowl or not. 

[carusoam]

Let’s invite the right Turbo Plus guy this time….     @Jeff Shapiro

Best regards,

-a-

[Red Leader]

I have been told it is the Turbo Plus intercooler. It does have a large scoop on the right front engine cowl to direct air over the intercooler.

[Phil EF]

A legal installation will include an update of the limitations section of the POH   
For Airflow Systems max continuous MAP is 37”.

Adhering to max power fuel flow is also important especially on the GB engine. 

[Pete M]

On 2/4/2022 at 3:34 AM, carusoam said:

I’m glad you thought to ask these questions…

Transition Training is a great way to get up to speed with everything you want to know…

 

Specifically…

I liked the number 2 question the most…

EGTs and CHTs are loosely connected…

And EGTs are loosely connected to TITs…

 

But, for the safety of the turbo’s health…

none of the CHT or EGTs can tell you what the TIT would actually be reading….

EGTs are highly dependent on location in an open ended tube… (nice to know about their sensitivity to everything)

EGTs are averaged over time… one flame front per two revolutions…

TITs are seeing six flame fronts in the same amount of time…. (Really affects the average temp that the gauge is reading)

Chts are on the cold side of the engine, and have very little in common with temps inside the hot side…

 

Now for the hard part…

You know there is a minimum equipment list right?

This list is in the POH… for your specific plane…

See if the TIT gauge is listed as a must have for day, night, VFR, or IFR flight…

For NA Mooneys… a single CHT is required but an EGT is not….

For TC’d Mooneys… if I owned the plane the TIT would be a requirement…

It is too easy to overheat the exhaust system of a TC’d engine…. Care should be taken to avoid the damage that gets caused by excessive wear… caused by extra heat….

Kind of a heads up and what to look for during your transition training…

At least find the MEL in the POH and see if the TIT is required for flight…

PP thoughts only, not a CFII…

-a-

 

Should be a "required equipment list" or a "kinds of operations list". An MEL is an faa approved letter issued to specific operators. Lots of confusion over this. Also, 91.205 applies so anything broken we check 91.205 to see if its required, then kinds of ops list and mel if issued. Private pilot training is my life:) Well, till April. I did it, I'm not proud, I sold out to da man, ...off to airline training end of april...

Pete

[Red Leader]

Both the CDT and TIT gauges will be repaired shortly (one broken wire, one failed probe) so I hope to be back in the air in a couple of days. Thanks again for all the helpful advice, you guys are great!

[Red Leader]

An interesting update: I believe this aircraft has flown previously using the EGT probe to read TIT. I stopped by the shop the other day and saw I have a single EGT probe (but I knew that already) that is installed just over an inch away from the TIT probe - both of which are mounted either on or immediately before the turbo. Given its location, I assume it would read and react the same manner as the probe feeding the actual TIT gauge. Also the CDT probe is just where the temp probe for the intercooler and because of their proximity, I believe they would've also read the same. Although my TIT/CDT gauge was out, do you agree the other systems would've shown equivalent numbers?

We looked over my books and found the Turbo-Plus intercooler installed in the mid-eighties so our records are all good. Just had the oil changed and it was also clean with no contaminants found in the filter. My consumption had been just about zero for the last ten hours, or so. I would think that is good but shouldn't there be a little consumption? I had the oil changed just before the 30-hour mark, what do you 231/252 guys feel is the best change interval?

Another question I have is that a couple of entries earlier in this topic refers to an "aftercooler". Is that different from an "intercooler" and if so, in what way? If it is a different item, would it benefit me to have one installed?

I LOVE having a turbocharged airplane and I see why many pilots say that once you go turbo, you never go back. My next airplane will likely be an Acclaim (I am already looking). 

[LANCECASPER]

3 hours ago, NewOldPilot said:

An interesting update: I believe this aircraft has flown previously using the EGT probe to read TIT. I stopped by the shop the other day and saw I have a single EGT probe (but I knew that already) that is installed just over an inch away from the TIT probe - both of which are mounted either on or immediately before the turbo. Given its location, I assume it would read and react the same manner as the probe feeding the actual TIT gauge. Also the CDT probe is just where the temp probe for the intercooler and because of their proximity, I believe they would've also read the same. Although my TIT/CDT gauge was out, do you agree the other systems would've shown equivalent numbers?

We looked over my books and found the Turbo-Plus intercooler installed in the mid-eighties so our records are all good. Just had the oil changed and it was also clean with no contaminants found in the filter. My consumption had been just about zero for the last ten hours, or so. I would think that is good but shouldn't there be a little consumption? I had the oil changed just before the 30-hour mark, what do you 231/252 guys feel is the best change interval?

Another question I have is that a couple of entries earlier in this topic refers to an "aftercooler". Is that different from an "intercooler" and if so, in what way? If it is a different item, would it benefit me to have one installed?

I LOVE having a turbocharged airplane and I see why many pilots say that once you go turbo, you never go back. My next airplane will likely be an Acclaim (I am already looking). 

6 of the 7 Mooneys I've owned have been turbo (one 231, one Encore, three Bravos, one Acclaim). I change oil at 25 hours.

Intercooler and aftercooler, two names for the same thing.

[carusoam]

Some answers to some of your questions…

1) In open ended exhaust pipes… where the exhaust pressure drops along the pipe… temps change with external cooling, and exhaust gas expansion….

2) A turbo isn’t really an open system until after the turbo vanes, and it’s not completely closed either… so using an EGT gauge after all of the six cylinder exhaust tubes come together will work pretty well as a TIT back-up…. Position is important for reliable operations info…

3) Terminology… you have an intercooler… but technically, it’s an aftercooler….  If you are hanging out with your mechanical engineering friends… and you want to impress them with your terminology….  You are going to want to know a few more technical terms like CR, and what MP controller you have….

4) It’s fun to have more details than required… CDTs are good… and temp leaving the intercooler is really nice…. This helps knowing if the intercooler is working properly… (they can get dirty, or a clamp can open…)

5) In the end… you want to know how many cfm and what temp it is, that are being delivered to the engine…

6) For best engine health… make sure you are following the engine operations guidance provided by the intercooler guy…. It is on top of the operations guidance originally supplied for the engine….

PP thoughts only, not a mechanic…

Best regards,

-a-