M20K 252 TSIO 360 - SB (Road to make it run LOP)

[Ragsf15e]

6 hours ago, Z W said:

When we updated from a JPI EDM 930 to a G500Txi for engine monitoring, pretty much all the CHTs, EGTs, and especially TIT readings changed significantly. Of note, the TITs read significantly higher at the same power settings, I think, anyways. Fuel flow changed from being displayed on a Shaden digital fuel flow display to also being shown on the G500Txi, and we kept the factory manifold pressure and RPM gauges, and they always read slightly different than the new digital display. So the power settings are likely not exactly the same.

My take away is that we're trying to measure with a level of precision never available nor intended by the designers of our 40+ year old engines. I think the probes in each customized installation may be in a slightly different spot and may come from different manufacturers. I keep this in mind when comparing my engine's performance to photos posted on the internet by others. Useful to compare but your mileage may vary (literally).

Good points.  One (not perfect) way is to compare airspeed between settings.  Obviously dissimilar airplanes will be different, but they shouldn’t be grossly different from each other or book values at the same power.

[Ragsf15e]

19 hours ago, Fix said:

I've timed my mags several times with flower pot and digital meter and piston pin.
Maybe I messed up, I've double checked it.
At least both mags are even, maybe could try to adjust both mags 1 degree.

At 29" 2300 RPM at 10.1g/h LOP I my TIT show just above 1550f on the analog gauge, most likley 1510-1560f range.
Maybe it's higher than "normal", but on the other side it's still well below 1650f and also if the reading is "higher" even if the real TIT should be lower I have a margin to ~1600-1610f were my personal limit is. 

If I had a very low TIT with a functional TIT probe, then I might get above 1650f with out knowing it?


On the Garmin G500, do you calibrate the TIT against the analog gauge or how does it work?
I can also see that your EGT is lower than mine, what would be normal EGT temp?

Is there any difference between JPI probes and Garmin Probes and the original Probes with read out?
 

I totally agree that your tit value is plenty good where it’s at.  I guess I was trying to think one step ahead but I didn’t articulate that…. At 10.1gph on a 220hp SB engine you’re running about 60% power (62.8%).  And that’s fine (and very efficient). However, it’s nice to be able to crank it up to say 70% or maybe even higher still LOP and take some extra knots when you want to.  I suspect if you run 11.2gph for 70% (increasing the mp to stay LOP), the tit is going to start getting uncomfortably high.  
 

I bet the new gami injectors will help though.  Your spread is better than mine now, and mine seems to run great lop up to at least 70%.

[Will.iam]

Tit will lower with lower rpm. I have .2 gami spread and jpi says 80 degrees lop before i get rough. But my limiting factor is TIT as i try to stay at 1550 or lower. For one reason drift of tit is milder at 1550. If i push it to 1580 or 1590 some times the drift will go up to 1600 my personal limit. So 1550 and i do not have to watch it so closely. Cht’s below 380 personal limit but that becomes harder to do above 15k or so. Cracking the cowl flaps keeps them inline but hate the 2 kt penalty. Trying different MP settings will surprisingly change the chts for example sometimes at 28” mp the cht will start going over 380 but if i push up the mp 31” it will come back down with the cowl fully closed which is my goal to avoid that extra drag. Really going deeper lop just slows the flame front down more which if you do not slow the rpm will just let more heat/flame out the exhaust and lose power. You can see the effect as tit goes up and cht temps go down as the heat is spending less time in the cyl and more time in front of the turbo. When i start to descend, i will lower my lop to 5 to 19 degrees lop so as to maximize the heat in the chts as the increase airflow from the descent will lower my chts to low 300’s if i don’t otherwise. 
also have you calibrated your fuelflow meter? My hokin meter is .8 gph off compared to my jpi reading as the jpi i can change the “k” factor via software but the hokins i would have to mechanically set some switches. After flying a tank empty and then putting in a known exact 5 gallons into that tank and then fly it empty again you can get the accuracy down to .1 accuracy which you need as each .1 increase in fuel flow while lop changes my tit by 10 to 15 degrees.  Just bumping the fuel mixture knob can move it 5 to 10 it really is touchy again why i shoot for 1550. 
i say this as even though you show the same fuel flow reading as someone else your fuel could be up to .8 off like my hokin totalizer and if you don’t know you would think you are at a power setting that you really are not because of inaccurate fuel flow. . 

[LANCECASPER]

On 12/1/2025 at 9:14 PM, Will.iam said:

Tit will lower with lower rpm. I have .2 gami spread and jpi says 80 degrees lop before i get rough. But my limiting factor is TIT as i try to stay at 1550 or lower. For one reason drift of tit is milder at 1550. If i push it to 1580 or 1590 some times the drift will go up to 1600 my personal limit. So 1550 and i do not have to watch it so closely. Cht’s below 380 personal limit but that becomes harder to do above 15k or so. Cracking the cowl flaps keeps them inline but hate the 2 kt penalty. Trying different MP settings will surprisingly change the chts for example sometimes at 28” mp the cht will start going over 380 but if i push up the mp 31” it will come back down with the cowl fully closed which is my goal to avoid that extra drag. Really going deeper lop just slows the flame front down more which if you do not slow the rpm will just let more heat/flame out the exhaust and lose power. You can see the effect as tit goes up and cht temps go down as the heat is spending less time in the cyl and more time in front of the turbo. When i start to descend, i will lower my lop to 5 to 19 degrees lop so as to maximize the heat in the chts as the increase airflow from the descent will lower my chts to low 300’s if i don’t otherwise. 
also have you calibrated your fuelflow meter? My hokin meter is .8 gph off compared to my jpi reading as the jpi i can change the “k” factor via software but the hokins i would have to mechanically set some switches. After flying a tank empty and then putting in a known exact 5 gallons into that tank and then fly it empty again you can get the accuracy down to .1 accuracy which you need as each .1 increase in fuel flow while lop changes my tit by 10 to 15 degrees.  Just bumping the fuel mixture knob can move it 5 to 10 it really is touchy again why i shoot for 1550. 
i say this as even though you show the same fuel flow reading as someone else your fuel could be up to .8 off like my hokin totalizer and if you don’t know you would think you are at a power setting that you really are not because of inaccurate fuel flow. . 

One thing to consider: On the ground what do your cowl flaps look like when they are at the "closed"  position that's shown on the instrument panel indicator?

If I remember correctly they should be about a 1/2" open. If not you will run too hot and lose a couple knots. In the test flights when developing the 252 they found that 1/2" open at the indicated "closed" position gave it the best cruise speed since the air going into the cowling had to have an exit to be efficient. 

Sometimes a well-meaning mechanic or owner will adjust the cowl flaps so they are really completely closed, which they shouldn't be.

Also if you have a known TIT probe (meaning new) you won't hurt anything if you set it at 1580 and it bumps up to 1600 as it varies. However I would be very suspect if it's an old probe since the probes  indicate low after they are burned up. 

[Will.iam]

On 12/2/2025 at 10:30 AM, LANCECASPER said:

One thing to consider: On the ground what do your cowl flaps look like when they are at the "closed"  position that's shown on the instrument panel indicator?

If I remember correctly they should be about a 1/2" open. If not you will run too hot and lose a couple knots. In the test flights when developing the 252 they found that 1/2" open at the indicated "closed" position gave it the best cruise speed since the air going into the cowling had to have an exit to be efficient. 

Sometimes a well-meaning mechanic or owner will adjust the cowl flaps so they are really completely closed, which they shouldn't be.

Also if you have a known TIT probe (meaning new) you won't hurt anything if you set it at 1580 and it bumps up to 1600 as it varies. However I would be very suspect if it's an old probe since the probes  indicate low as they after they are burned up. 

Lance as always thanks for the researched tip! I had no idea there should be a 1/2 in gap fully closed! Mine do close flush. Will have to fix that but before i do that i am going to do an interesting test as i will do some speed runs at different “slightly” open configurations and if i can squeeze out a faster knot or 2 i will leave it there and land and take a measurement (hopefully remember a picture too) and post the results. 

[LANCECASPER]

39 minutes ago, Will.iam said:

Lance as always thanks for the researched tip! I had no idea there should be a 1/2 in gap fully closed! Mine do close flush. Will have to fix that but before i do that i am going to do an interesting test as i will do some speed runs at different “slightly” open configurations and if i can squeeze out a faster knot or 2 i will leave it there and land and take a measurement (hopefully remember a picture too) and post the results. 

Bob Kromer, the test pilot for the 252, gave presentations at MooneyMax in 2022 and 2024 where he told us about that. 



In 2024 at MooneyMax we were touring the factory on Saturday morning and I noticed a picture of the 252 from back in 1985/6. I asked Bob if that was him in the picture . .  sure enough it was. I think you'll also notice in the picture if you enlarge it that the cowl flaps are "closed", but in 1/2 inch trail as recommended.
 
Later that night Bob was nice enough to get in the picture with a couple of 252 owners, @MarcJohnson (L) and @shawnd (far R) and an Encore owner @Marc_B (C) .

[Will.iam]

Well i checked today and sure enough my cowl flap closes flush to the bottom so before i was going to adjust it for 1/2” opening i decided to go fly first. First problem i had to figure out is that when you run the cowl flaps down a little there is some serious slop at least on my cowls anyways. So i could move the cowl a good 2” with the play it had. Only after multiple landings and reverification (is that a word?) did i realize my cowl flap indicator is tied to the actual cowl flap itself so if i move it up it would indicate that as well as when i moved it down. Because in the past i always had it fully open i never noticed this movement at a partial cowl flap setting and at first i assumed the wind blast would try to push the cowlflap to the closed position but literally just the opposite happened. Apparently the amount of pressure coming into the openings of the cowl inlets by the prop forces the cowl flap open as far as it will go and has a stronger overwhelming force than the slipstream that flows around the outside of the cowling.  Having figured all that out, ironically today i was faster with the cowl fully closed than when i opened it a 1/2”. Now it was bumpy and i was only at 2500ft so maybe when I’m up in altitude where it is smooth i might get a better reading. Even if it stays the same speed with the cowl open 1/2” would be a win as up in the teens i struggle with keeping the cyl temps below 380 with fully close cowl flap. Will do further testing when i get the chance at a higher cruise altitude. 

[Ragsf15e]

13 hours ago, Will.iam said:

Well i checked today and sure enough my cowl flap closes flush to the bottom so before i was going to adjust it for 1/2” opening i decided to go fly first. First problem i had to figure out is that when you run the cowl flaps down a little there is some serious slop at least on my cowls anyways. So i could move the cowl a good 2” with the play it had. Only after multiple landings and reverification (is that a word?) did i realize my cowl flap indicator is tied to the actual cowl flap itself so if i move it up it would indicate that as well as when i moved it down. Because in the past i always had it fully open i never noticed this movement at a partial cowl flap setting and at first i assumed the wind blast would try to push the cowlflap to the closed position but literally just the opposite happened. Apparently the amount of pressure coming into the openings of the cowl inlets by the prop forces the cowl flap open as far as it will go and has a stronger overwhelming force than the slipstream that flows around the outside of the cowling.  Having figured all that out, ironically today i was faster with the cowl fully closed than when i opened it a 1/2”. Now it was bumpy and i was only at 2500ft so maybe when I’m up in altitude where it is smooth i might get a better reading. Even if it stays the same speed with the cowl open 1/2” would be a win as up in the teens i struggle with keeping the cyl temps below 380 with fully close cowl flap. Will do further testing when i get the chance at a higher cruise altitude. 

Mine is set fully closed as well.  It also “seems” a knot or two faster there than if it’s open slightly.  But I haven’t done real good testing on that.  I haven’t had cooling issues running lop and flying in the teens except in the dead of summer.  Usually it’s still cool up there in the northwest where I live.

[Will.iam]

9 hours ago, Ragsf15e said:

Mine is set fully closed as well.  It also “seems” a knot or two faster there than if it’s open slightly.  But I haven’t done real good testing on that.  I haven’t had cooling issues running lop and flying in the teens except in the dead of summer.  Usually it’s still cool up there in the northwest where I live.

Yes winter time it’s easier to keep the cyl temps down. Seems only in the summer or huge temp inversion do i struggle with the thinner air at alt to keep cool. 

[LANCECASPER]

14 hours ago, Will.iam said:

Yes winter time it’s easier to keep the cyl temps down. Seems only in the summer or huge temp inversion do i struggle with the thinner air at alt to keep cool. 

In early 2014 I bought a 1997 M20K (Encore) with about 750 TT. The cylinders had been replaced with new Continental cylinders before I bought it at around 645 hours.



 
When we took the top cowling off the first thing I noticed was that the rear baffling material was "lazy" and blowing back, meaning that almost no air was being forced down over the cylinders. During the annual I had them replace the baffling with Gee Bee baffles. Over the next month or so a few pleats had to be cut to get them to lay perfectly, but I never had a problem with the cylinders overheating during the summer in Texas.