Hottest cylinder CHT at cruise

[Ragsf15e]

1 hour ago, A64Pilot said:

Ideal would be a timing switch so you could run 20 on takeoff and when climbing at TO power and a way to advance once in cruise, graduate level would be to do it based on manifold pressure.

You can.  Install a Surefly mag.  You described the advance mapping almost perfectly.  There are some people who aren’t fans, and that’s fine, but it does almost exactly as you describe. It even use MP.  It would be nice to have both mags do it though.

[A64Pilot]

59 minutes ago, Ragsf15e said:

You can.  Install a Surefly mag.  You described the advance mapping almost perfectly.  There are some people who aren’t fans, and that’s fine, but it does almost exactly as you describe. It even use MP.  It would be nice to have both mags do it though.

I don’t believe I have that option as I have the one big mag.

But in all honesty the number of hours I fly, it’s likely it would never pay for itself as I don’t believe the fuel savings are that great and there are other issues too, like changing timing changes the vibrations an engine makes and this can cause issues with propellors. When a vibe survey is conducted, it’s conducted at stock conditions, I’ve been a part of STC’s, you would be surprised at what slips by. Assumption is the allowable timing change is smaller than optimum to mitigate those other issues?

Plus comparing our engines to auto engines isn’t really valid, the Buick from years ago operated at much wider load and RPM than we do, so while there are gains with our aircraft motors, they aren’t as great as they are in auto motors. They are there, just not as big a difference

Someone here made the comparison that our engines are essentially similar to stationary engines, and that was actually a very astute comparison I believe. I cruise for example between 2200 and 2500 myself and believe I’m not uncommon, fixed timing with only a 300 RPM band is or can be pretty close. Truth is I’m between 2200 and 2300 99% of the time.

But for me it really boils down to cost, if someone were to come out with a real electronic variable ignition system for my airplane and it cost $5,000 all in including all expenses and it saved 1 GPH (which is pretty close to 10% and 10% would be HUGE, it would still take almost 10 years to break even with my 100 hour a year flying.

500 hour mag inspections would factor in too of course, but still the payback would be a long time.

I have no clue what a full electronic ignition would cost, just threw $5K out there, and I doubt 10% is doable, cause that’s a big number, and maybe fuel will be $10 a gl soon and that would factor in too, so take all the numbers with a grain of salt, meant to be representative is all.

[Shadrach]

3 hours ago, A64Pilot said:

Increasing timing, you WILL increase HP, and should / may decrease BSFC some.

Increased HP WILL increase cyl head temp, and it WILL reduce detonation margin, on edit detonation is the limit for timing advance, hence modern automobiles have detonation sensors and will often run right at the limit of detonation. Cooling is also a limit of course.

Lycoming decreased timing because they learned they could still make the HP requirement and the engine ran cooler, and running cooler it would last longer. I don’t think you will find that in writing.

This is when the engine was operated IAW Lycoming recommendations, which is run pretty hard and either peak or ROP, don’t operate it that way and of course things may or may not change.

Ideal would be a timing switch so you could run 20 on takeoff and when climbing at TO power and a way to advance once in cruise, graduate level would be to do it based on manifold pressure.

I believe almost 100 years ago Buick figured this out and fitted a vacuum advance on their distributor that would advance timing when loads were low and significantly increase economy, our 1923 Model T your in charge of timing, the lever is under the steering wheel on the left side, retard to start, normal cruise full advance, hill climbing retard some or it will overheat. 

I’m not sure where your narrative about Lycoming engineers “discovering that they could reduce timing and still make the same power”, but it reads more like an opinion in search of a supporting story rather than history. The rumor that Lycoming reduced timing as a bandaid to help an airframe manufacturer meet cooling requirements seems way more plausible than a group of highly educated engineers having a eureka moment at some point in the 70s/80s about an aspect of internal combustion that was well understood in the 1930s... 
 

While you’re absolutely correct about how timing affects power and CHTs,  I’m not really sure how you square that with your notion of rated power. Either it was making more than 200 hp when it was certified at 25° or it is making less than 200 hp at 20°. My guess is there is enough fudge factor in the number to keep the Feds from caring.

If you have a source of information about Lycoming‘s “Eureka!” Timing discovery, please link it so we can all read about this “free lunch”.

What you say about timing and CHT’s is  true, but it’s only part of the story.  25° is not an aggressively advanced setting for the RPM ranges in which our engines operate. Even with the apparently “sub optimal” cowling on my vintage F, my engine runs very cool. Indeed so cool, I don’t think I would want it to run much cooler. Maybe you’re right. Maybe I would see a significant increase in engine longevity taking my summertime CHT’s from the low 300s into the high 200s, but I don’t think there’s any evidence to support that supposition. There is a healthy range with which to operate cylinders, either you’re in it or you’re not. You speak about CHTs in engine health like there’s a linear correlation between CHT and cylinder life. I don’t think it’s linear at all. If plotted on a graph, I think it would look like “U”  with cylinder life decreasing at very cool and very hot temperatures. 

 

[A64Pilot]

You get awfully sarcastic don’t you?

Its not at all uncommon for an engine in one aircraft model to have different settings to satisfy the requirements for that airframe. Just as it’s not uncommon for the engine to have different avoid ranges by propellor and airframe combinations, so if one airframe manufacturer had temp issues it’s not a stretch to see a different timing or even a different model of engine for that manufacturer, model difference being timing. Look at how many different models that make essentially the same power there are now.

However I think it would be uncommon for Lycoming or any manufacturer to handicap an entire product line for one customer don’t you think?

Your low CHT is more likely due to LOP operation and the resultant lower power output than timing, run her at high power down low at 100 ROP at high OAT in a Vx climb and report your temps. I know my J with its 20 degree timing can easily get close to redline with cowl flaps open in a VX climb on a hot day, does your F at 25 not?

Do F model’s have a reputation of running exceedingly cool head temps?

Yes it was making in excess of 200HP on average at 25 timing, how else can you explain it still makes rated power (200) at 20 degrees? Do you think they changed compression, valve timing or what? Best way for a manufacturer to make specification power is to exceed it by a significant margin, cause if they don’t make it, they have to reduce the rating or start making changes and start retesting. No one complains if you give them more than they asked for, but don’t meet specs even by a tiny bit and there will be problems.

As the AH-64 got heavier in mission gross weight, went from 17,650 lbs to 21,000 lbs, engine performance got much more important as we were operating in very hot and often high conditions, we needed to know exactly how much power each engine could make, where before we used charts that were based on Rated Power. Our test flights merely determined that an engine could produce rated power, how much more who knew or cared. We began to care in the Desert and I heard Afghanistan was even worse.

So we began determining what was called Specification torque ratio for each engine and the average of the two was called Airframe Torque Ratio, this enabled the pilots doing performance planning to determine for instance that their engines were slightly stronger or weaker than the “average” engine that the performance planning charts were determined from and given a number that they could adjust from the knew exactly when their engines would limit out.

I would establish 100% torque and climb until rotor RPM decayed meaning the engines were at max power, then recording the numbers and using charts the STR was determined and the ATR was simply an average of the two STR’s

Guess what? Even though I had the oldest aircraft in the fleet at the time, an average engine produced about 106% Specification Torque Ratio, meaning they exceeded rated power by 6%, even at their age. New engines could easily be 10%. That’s not uncommon for engines to produce in excess of rated power. Can you imagine how hard it would be to produce an entire fleet of engines with all of them just barely making it? A whole lot easier to have a fudge factor.

None of my engines didn’t make rated power even though most had over 2,000 hours on them.

I even had one engine in Germany that wouldn’t limit, our charts only went to 12,000 ft and at 12K this motor would still pull the transmission torque limit, I had to get a letter from GE saying that’s it’s OK to have an engine that strong to put in the aircrafts records. That only happened once though, it was over 10% stronger than rated power.

[A64Pilot]

I can’t find Lycoming SI 1325A, but this may help, apparently he was a Lycoming guy

https://generalaviationnews.com/2021/12/08/what-timing-should-i-use-in-my-engine/

 

This is Mike Busch’s take on the reduction from 25 to 20 timing. https://www.aopa.org/news-and-media/all-news/2021/october/pilot/savvy-maintenance-hot-heads

“The Lycoming IO-360-series offers an interesting case study. When the IO-360 was originally certified, Lycoming specified that the magneto timing be set to 25 degrees BTDC—a relatively aggressive value. But the engines had so many issues with excessive CHTs that Lycoming subsequently issued a service bulletin authorizing the engine timing to be retarded to 20 degrees BTDC. Making this timing change had an insignificant effect on horsepower but a dramatic improvement in CHT. Since the timing change was authorized by noncompulsory service bulletin rather than compulsory airworthiness directive, we now have a mixture of IO-360s flying, some timed to 25 degrees BTDC and some to 20 degrees BTDC. When I generate a CHT histogram of the thousands of IO-360s in our database, I see two distinct peaks in the data.

Curiously, the Lycoming service bulletin applied only to the IO-360 family, not the O-360s, O/IO-320s, or O/IO-540s, all of which remain specified at 25 degrees BTDC. I’ve counseled numerous operators of RVs and other experimental aircraft using these engines to try retarding their ignition timing by a couple of degrees, and they’ve been very pleased with the results. I can’t really offer the same advice to operators of certified aircraft, but at least backing the timing off to 24 degrees BTDC (the bottom of the tolerance band) will provide some improvement.”

[Shadrach]

On 7/3/2022 at 4:22 PM, A64Pilot said:

You get awfully sarcastic don’t you?

Its not at all uncommon for an engine in one aircraft model to have different settings to satisfy the requirements for that airframe. Just as it’s not uncommon for the engine to have different avoid ranges by propellor and airframe combinations, so if one airframe manufacturer had temp issues it’s not a stretch to see a different timing or even a different model of engine for that manufacturer, model difference being timing. Look at how many different models that make essentially the same power there are now.

However I think it would be uncommon for Lycoming or any manufacturer to handicap an entire product line for one customer don’t you think?

Your low CHT is more likely due to LOP operation and the resultant lower power output than timing, run her at high power down low at 100 ROP at high OAT in a Vx climb and report your temps. I know my J with its 20 degree timing can easily get close to redline with cowl flaps open in a VX climb on a hot day, does your F at 25 not?

Do F model’s have a reputation of running exceedingly cool head temps?

Yes it was making in excess of 200HP on average at 25 timing, how else can you explain it still makes rated power (200) at 20 degrees? Do you think they changed compression, valve timing or what? Best way for a manufacturer to make specification power is to exceed it by a significant margin, cause if they don’t make it, they have to reduce the rating or start making changes and start retesting. No one complains if you give them more than they asked for, but don’t meet specs even by a tiny bit and there will be problems.

As the AH-64 got heavier in mission gross weight, went from 17,500 lbs to 21,000 lbs, engine performance got much more important as we were operating in very hot and often high conditions, we needed to know exactly how much power each engine could make, where before we used charts that were based on Rated Power. Our test flights merely determined that an engine could produce rated power, how much more who knew or cared. We began to care in the Desert and I heard Afghanistan was even worse.

So we began determining what was called Specification torque ratio for each engine and the average of the two was called Airframe Torque Ratio, this enabled the pilots doing performance planning to determine for instance that their engines were slightly stronger or weaker than the “average” engine that the performance planning charts were determined from and given a number that they could adjust from the knew exactly when their engines would limit out.

I would establish 100% torque and climb until rotor RPM decayed meaning the engines were at max power, then recording the numbers and using charts the STR was determined and the ATR was simply an average of the two STR’s

Guess what? Even though I had the oldest aircraft in the fleet at the time, an average engine produced about 106% Specification Torque Ratio, meaning they exceeded rated power by 6%, even at their age. New engines could easily be 10%. That’s not uncommon for engines to produce in excess of rated power. Can you imagine how hard it would be to produce an entire fleet of engines with all of them just barely making it? A whole lot easier to have a fudge factor.

None of my engines didn’t make rated power even though most had over 2,000 hours on them.

I even had one engine in Germany that wouldn’t limit, our charts only went to 12,000 ft and at 12K this motor would still pull the transmission torque limit, I had to get a letter from GE saying that’s it’s OK to have an engine that strong to put in the aircrafts records. That only happened once though, it was over 10% stronger than rated power.

I apologize if my post came off sarcastic. The bit about disbelief that Lycoming “discovered” that their engine engine still made rated power with timing retarded 5° could have been worded better.  I have been flying this particular air frame for 20 years. I’ve been through it from spinner to tail. I can say unequivocally that at 25° it has excellent cooling characteristics and detonation margins at all power settings as long as the baffles and seals are properly installed and maintained. Temps need to be monitored but require very little management regardless of mixture setting.  Much like one's preferred power settings, I don’t care how someone has their engine timed. What I find slightly perturbing is the misinformation about the subject. Which includes but is not limited to the following:

1) “Lycoming changed the timing specs to increase engine longevity.”
This is pure speculation. I’ve not been able to find anything from Lycoming describing why they made 20° an option nor why they started delivering all factory engines that way. As I said, there are rumors that it was done for a specific application.

2) ”timing really isn’t that important. It’s a fuzzy number. A 5° reduction in advance isn’t really going to affect power noticeably.” 
It seems incoherent to suggest that a 5° reduction in advance makes for a significant increase in detonation margin and significant decrease in temps while at the same time suggesting the power difference is insignificant.

3) “20° is the more ideal setting, that’s why the factory sets all of their engines that way”. 
I kid you not, I had a mechanic once tell me that the TCDS specified 20° as optimal. I pulled it up on my phone so he could see that he was mistaking the word “optional” for optimal. 

I can go on but I will just sumerise by saying that people spend tons of money on aerodynamic tweaks to pick up 5 kts. Or spend thousands on an Emag to get increased performance. They will embark on these modifications without even considering that perhaps there’s some low hanging fruit to be picked. For those that like to operate on the lean side of peak the extra 5° makes a considerable difference in engine smoothness and power when operating in that part of the mixture spectrum. The costs are minimal and it’s easy to switch back if you don’t like it. Yet the “you’ll shoot your eye out“ sentiment prevails. Not just here but within the Aircraft maintenance community. Most of the detractors have never run an IO360 that’s timed to 25° yet they have very strong opinions about the utility of doing so.

[Shadrach]

19 minutes ago, A64Pilot said:

I can’t find Lycoming SI 1325A, but this may help, apparently he was a Lycoming guy

https://generalaviationnews.com/2021/12/08/what-timing-should-i-use-in-my-engine/

 

This is Mike Busch’s take on the reduction from 25 to 20 timing. https://www.aopa.org/news-and-media/all-news/2021/october/pilot/savvy-maintenance-hot-heads

“The Lycoming IO-360-series offers an interesting case study. When the IO-360 was originally certified, Lycoming specified that the magneto timing be set to 25 degrees BTDC—a relatively aggressive value. But the engines had so many issues with excessive CHTs that Lycoming subsequently issued a service bulletin authorizing the engine timing to be retarded to 20 degrees BTDC. Making this timing change had an insignificant effect on horsepower but a dramatic improvement in CHT. Since the timing change was authorized by noncompulsory service bulletin rather than compulsory airworthiness directive, we now have a mixture of IO-360s flying, some timed to 25 degrees BTDC and some to 20 degrees BTDC. When I generate a CHT histogram of the thousands of IO-360s in our database, I see two distinct peaks in the data.

Curiously, the Lycoming service bulletin applied only to the IO-360 family, not the O-360s, O/IO-320s, or O/IO-540s, all of which remain specified at 25 degrees BTDC. I’ve counseled numerous operators of RVs and other experimental aircraft using these engines to try retarding their ignition timing by a couple of degrees, and they’ve been very pleased with the results. I can’t really offer the same advice to operators of certified aircraft, but at least backing the timing off to 24 degrees BTDC (the bottom of the tolerance band) will provide some improvement.”

I would love to have a chat with Mike about the data. I am absolutely certain that the parallel valve carbureted engines would reap significant benefits from a reduction in timing. They tend to run hot. The injected Angle valves engines, not at all in my experience. Maybe I’ll drop Mike a line and see if he responds.

[A64Pilot]

It’s my belief that cyl head temp tracks power output more than anything else, it’s not EGT, I can run higher EGT at lower power settings and run cooler cyl head temps, and of course run pretty cool EGT at high power and much hotter cyl head temps. It could also be that I never hang one on the prop climbing. I usually increase speed until I get 500 FPM or so, I call it a cruise climb, but speed does help keep things cooler.

Only one of those quotes you made I believe that I said and that was the one about the engine will last longer with 20 timing than 25. It will most assuredly if run IAW the POH because within reason pretty much everyone agrees that cooler means less stress and less stress means longer life, increase timing and if everything else is identical and you will increase cyl head temps. Not saying you can’t keep it within limits, but everything else being equal, the more advanced motor will be running hotter, should be making more power too, but maybe not much because there is a point of diminishing returns and I have no idea where that point is.

However I also said those statements are true if you run the thing IAW the POH and to Lycoming recommendations, which are ROP and peak, not LOP. Run it outside of those recommendations and things may / will change of course

Running LOP does change things, slower flame front travel and increased time to peak pressure being one or two actually, I won’t disagree that to maintain peak pressure where you want it to be would likely mean advanced timing when LOP, and power is reduced and reduced power may likely wash out increased heat from advanced timing.

A problem with that though is you have to keep that advanced timing for T/O and climb.

Mike said in that article that they track thousands of IO-360’s and that the ones with advanced timing are evident in cyl head temps, he said the two different timing settings make themselves known by temps, paraphrased of course. I don’t remember his exact wording.

I’d be very surprised if in fact he tracks thousands of angle valve IO-360’s myself, I fell that may be a little bit of an exaggeration. But I would be surprised if they were run in identical conditions that the advanced timing didn’t run hotter. Not saying too hot if you maintain things and keep an eye on it. Not saying 25 is unsafe, just hotter at high power settings than 20 is.

[TigerMooney]

On 7/2/2022 at 1:07 PM, Shadrach said:

This was my impetus for tweaking. The two coolest jugs, #1 and #4 run 300° +/-10 in the summer and track pretty close together. It takes work to get them up to 300° in winter.  Prior to tweaking the delta in temp during climb between #1 (coolest) and #3 (hottest) was >60°, now it’s more like 35° and tracks so close to #2 in cruise that they trade places as hottest cyl depending on mixture setting.

First time poster here….This closely describes my 1981 M20J with an IO-360. I just bought it last week and have only put 7 hours on it. Has EDM 700, and in cruise #3 is hottest, with #2 sometimes being close. I have to go 150-200+ ROP to get the temps below 380 (and they’ll hang in the 370s). I sometimes will open the cowl flaps partially to get more air flow, while I’m trying to figure it all out. If I lean 50-100 ROP it gets in excess of 390 rather quick, but I also notice the fuel flow seems rather low for a given power setting per the book.

 

Obviously I’m still very new to the plane, but it sounds like I should look at the baffling? The mechanic in the Pre Buy took both the top and bottom cowlings off - and maybe they were not seated properly when they were put back on? I’m not entirely sure what I’m looking for, if I were to look at it myself.  

 

I’m operating it in the warmer southeastern temps (mid 80s to mid 90s on the ground) so obviously its going to be hot anyway. Are there and specific Mooney tips for leaning on the ground/takeoff/climb?

 

Also, is it general practice to use the electric fuel pump on every takeoff/landing? In other airframe types, it’s been recommended not to use them, as sometimes the fuel pump themself can break up and cause a fuel like blockage. 

 

Thanks in advance, and sorry for the long post!

[jetdriven]

On 7/3/2022 at 6:36 PM, Shadrach said:

I apologize if my post came off sarcastic. The bit about disbelief that Lycoming “discovered” that their engine engine still made rated power with timing retarded 5° could have been worded better.  I have been flying this particular air frame for 20 years. I’ve been through it from spinner to tail. I can say unequivocally that at 25° it has excellent cooling characteristics and detonation margins at all power settings as long as the baffles and seals are properly installed and maintainedTemps need to be monitored but require very little management regardless of mixture setting.  Much like power setting, I don’t care how someone has their engine timed. What I find slightly perturbing is the misinformation about the subject. Which includes but is not limited to the following:

1) “Lycoming changed the timing specs to increase engine longevity.”
This is pure speculation. I’ve not been able to find anything from Lycoming describing why they made 20° an option nor why they started delivering all factory engines that way. As I said, there are rumors that it was done for a specific application.

2) ”timing really isn’t that important. It’s a fuzzy number. A 5° reduction in advance isn’t really going to affect power noticeably.” 
It seems incoherent to suggest that a 5° reduction in advance makes for a significant increase in detonation margin and significant decrease in temps while at the same time suggesting the power difference is insignificant.

3) “20° is the more ideal setting, that’s why the factory sets all of their engines that way”. 
I kid you not, I had a mechanic once tell me that the TCDS specified 20° as optimal. I pulled it up on my phone so he could see that he was mistaking the word “optional” for optimal. 

I can go on but I will just sumerise by saying that people spend tons of money on aerodynamic tweaks to pick up 5 kts. Or spend thousands on an Emag to get increased performance. They will embark on these modifications without even considering that perhaps there’s some low hanging fruit to be picked. For those that like to operate on the lean side of peak the extra 5° makes a considerable difference in engine smoothness and power when operating in that part of the mixture spectrum. The costs are minimal and it’s easy to switch back if you don’t like it. Yet the “you’ll shoot your eye out“ sentiment prevails. Not just here but within the Aircraft maintenance community. Most of the detractors have never run an IO360 that’s timed to 25° yet they have very strong opinions about the utility of doing so.

I agree, it's magical thinking to think that 20° of timing makes the same power as 25. When we bought our plane we noted it was a complete dog on takeoff and climb and cruise, but we figured there was probably some optimization or it was a tired engine.  Come to find out the dual magneto at 20° which is not even allowed, putting it back where it was supposed to be made us 5 kn in cruise and it would actually run lean of peak whereas before the speed would fall off right proportionally with fuel flow.  for your hot running engine, fix the cooling deficiency, instead of covering it up with the Band-Aid by derating your engine

[Shadrach]

5 minutes ago, jetdriven said:

I agree, it's magical thinking to think that 20° of timing makes the same power as 25. When we bought our plane we noted it was a complete dog on takeoff and climb and cruise, but we figured there was probably some optimization or it was a tired engine.  Come to find out the dual magneto at 20° which is not even allowed, putting it back where it was supposed to be made us 5 kn in cruise and it would actually run lean of peak whereas before the speed would fall off right proportionally with fuel flow.  for your hot running engine, fix the cooling deficiency, instead of covering it up with the Band-Aid by derating your engine

It's good to read someone speaking from actual experience. Your experience mirrors mine.  I believe Mike @201er had a similar "why is this so doggy compared to the old engine" experience after hanging a fresh engine on his plane.

[jetdriven]

There is some speculation that the roller cam engine made more power than rated, so they effectively de-rated the engine by changing the cam profile or advancing the camshaft. But a roller cam engine running at  20° is quite noticeably slower than a A3B6D engine running at 25 degrees.  Actually, around 23-24° is the best timing for these roller engines.

[jetdriven]

6 minutes ago, Shadrach said:

It's good to read someone speaking from actual experience. Your experience mirrors mine.  I believe Mike @201er had a similar "why is this so doggy compared to the old engine" experience after hanging a fresh engine on his plane.

Mike's plane is in my shop right now for its second annual here. He and I had the same experience when we both put factory engines on our planes 7 years ago, and putting Bendix mags on it and turning it up made a big difference.

[Shadrach]

2 minutes ago, jetdriven said:

There is some speculation that the roller cam engine made more power than rated, so they effectively de-rated the engine by changing the cam profile or advancing the camshaft. But a roller cam engine running at  20° is quite noticeably slower than a A3B6D engine running at 25 degrees.  Actually, around 23-24° is the best timing for these roller engines.

It's a shame Lycoming did not specify a range. If 20° and 25° are approved, anything in between is acceptable.  My A&P busies himself with other things until I have finished timing a mag. He thinks I am overly fastidious. I am happy to take a little extra time to ensure I have set the maximum advance that can be read as 25°. 

 

[N201MKTurbo]

I run mine at 25 degrees. It runs LOP much happier than 20. 

[PT20J]

According to Lycoming, a requirement for the roller tappet engines was that they had to meet all the same specs including rated power else they would have had to recertify them. The issue is that the cam profile is different for the roller tappets -- more rounded ramps and flatter nose. They couldn't make it work for the turbos which is why turbos still have mushroom lifters. The rollers have little effect on the top end of the IO-360 -- maybe a hair more power but nothing you would notice -- but there is a change in the idle and the roller engines idle closed throttle at an inch or two higher MAP.

I don't know what to make of the 20 deg vs 25 deg thing. I believe those of you that say you experienced performance differences. I didn't notice any difference when I replaced the A3B6D (25 deg) with a -A3B6 (20 deg). But they were different engines and one was old and one was new. Lycoming claims both timings meet spec. And all my internal combustion engine textbooks show that the power difference between MBT timing and +/-5 deg is only a couple percent -- the power vs timing curve is pretty flat around the peak. I suppose it is possible that MBT timing is more like 30 BTDC, and it was originally backed off for detonation margin, in which case 20 degrees would be pretty far off optimum. Maybe someday I will try running my engine at 25 and see what difference it makes.

Skip

[Shadrach]

46 minutes ago, PT20J said:

I suppose it is possible that MBT timing is more like 30 BTDC, and it was originally backed off for detonation margin

I believe this to be the case. Nigel Speedy's raw data seems to support this supposition. For ops at 25LOP his data suggests 35 BDTC is closer to ideal.

[Shadrach]

3 hours ago, TigerMooney said:

First time poster here….This closely describes my 1981 M20J with an IO-360. I just bought it last week and have only put 7 hours on it. Has EDM 700, and in cruise #3 is hottest, with #2 sometimes being close. I have to go 150-200+ ROP to get the temps below 380 (and they’ll hang in the 370s). I sometimes will open the cowl flaps partially to get more air flow, while I’m trying to figure it all out. If I lean 50-100 ROP it gets in excess of 390 rather quick, but I also notice the fuel flow seems rather low for a given power setting per the book.

 

Obviously I’m still very new to the plane, but it sounds like I should look at the baffling? The mechanic in the Pre Buy took both the top and bottom cowlings off - and maybe they were not seated properly when they were put back on? I’m not entirely sure what I’m looking for, if I were to look at it myself.  

 

I’m operating it in the warmer southeastern temps (mid 80s to mid 90s on the ground) so obviously its going to be hot anyway. Are there and specific Mooney tips for leaning on the ground/takeoff/climb?

 

Also, is it general practice to use the electric fuel pump on every takeoff/landing? In other airframe types, it’s been recommended not to use them, as sometimes the fuel pump themself can break up and cause a fuel like blockage. 

 

Thanks in advance, and sorry for the long post!

Your engine is running 40-50 warmer than my F at similar OATs.  Ensuring the baffle seals are in good shape and properly oriented is the first order of business.

[PT20J]

1 hour ago, Shadrach said:

I believe this to be the case. Nigel Speedy's raw data seems to support this supposition. For ops at 25LOP his data suggests 35 BDTC is closer to ideal.

Yes, but his engine has the 10:1 pistons. Not sure what effect that might have. 

[Will.iam]

7 hours ago, PT20J said:

According to Lycoming, a requirement for the roller tappet engines was that they had to meet all the same specs including rated power else they would have had to recertify them. The issue is that the cam profile is different for the roller tappets -- more rounded ramps and flatter nose. They couldn't make it work for the turbos which is why turbos still have mushroom lifters. The rollers have little effect on the top end of the IO-360 -- maybe a hair more power but nothing you would notice -- but there is a change in the idle and the roller engines idle closed throttle at an inch or two higher MAP.

I don't know what to make of the 20 deg vs 25 deg thing. I believe those of you that say you experienced performance differences. I didn't notice any difference when I replaced the A3B6D (25 deg) with a -A3B6 (20 deg). But they were different engines and one was old and one was new. Lycoming claims both timings meet spec. And all my internal combustion engine textbooks show that the power difference between MBT timing and +/-5 deg is only a couple percent -- the power vs timing curve is pretty flat around the peak. I suppose it is possible that MBT timing is more like 30 BTDC, and it was originally backed off for detonation margin, in which case 20 degrees would be pretty far off optimum. Maybe someday I will try running my engine at 25 and see what difference it makes.

Skip

Hey skip did you get to ask lycoming about timing 25 vs 20 degrees at your lycoming class?

[Wildhorsetrail]

First time poster here….This closely describes my 1981 M20J with an IO-360. I just bought it last week and have only put 7 hours on it. Has EDM 700, and in cruise #3 is hottest, with #2 sometimes being close. I have to go 150-200+ ROP to get the temps below 380 (and they’ll hang in the 370s). I sometimes will open the cowl flaps partially to get more air flow, while I’m trying to figure it all out. If I lean 50-100 ROP it gets in excess of 390 rather quick, but I also notice the fuel flow seems rather low for a given power setting per the book.
 
Obviously I’m still very new to the plane, but it sounds like I should look at the baffling? The mechanic in the Pre Buy took both the top and bottom cowlings off - and maybe they were not seated properly when they were put back on? I’m not entirely sure what I’m looking for, if I were to look at it myself.  
 
I’m operating it in the warmer southeastern temps (mid 80s to mid 90s on the ground) so obviously its going to be hot anyway. Are there and specific Mooney tips for leaning on the ground/takeoff/climb?
 
Also, is it general practice to use the electric fuel pump on every takeoff/landing? In other airframe types, it’s been recommended not to use them, as sometimes the fuel pump themself can break up and cause a fuel like blockage. 
 
Thanks in advance, and sorry for the long post!

I had some concerns about the old baffling on my 1979 J so I put all new seals on from GeeBee. They were a great fit, but did very little to the temperatures. The thing that actually made a noticeable difference was putting some seal across the "v" below the deleted ram air. As some others here have noted, there is a significant gap in that area if the ram is gone.

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[PT20J]

18 minutes ago, Will.iam said:

Hey skip did you get to ask lycoming about timing 25 vs 20 degrees at your lycoming class?

Lycoming's position is that the engine meets specs at 20 degrees. The rationale of the change is in the original pub. 

SI 1325 Timing Change for IO-360 Series Engines.pdf

[TigerMooney]

On 9/21/2022 at 12:32 AM, Wildhorsetrail said:

I had some concerns about the old baffling on my 1979 J so I put all new seals on from GeeBee. They were a great fit, but did very little to the temperatures. The thing that actually made a noticeable difference was putting some seal across the "v" below the deleted ram air. As some others here have noted, there is a significant gap in that area if the ram is gone.

Sent from my SM-A326U1 using Tapatalk
 

Interesting. I still have the ram air, however the rubber seal around the bottom is sort of chewed up and loose. Maybe that will help. It’s still really strange to me that I have to run it so rich to keep the temps down. I’ll keep trying one thing at a time until I get it right.

[Tx_Aggie]

On 9/23/2022 at 9:09 PM, TigerMooney said:

Interesting. I still have the ram air, however the rubber seal around the bottom is sort of chewed up and loose. Maybe that will help. It’s still really strange to me that I have to run it so rich to keep the temps down. I’ll keep trying one thing at a time until I get it right.

I live in western texas. The trick for me was adjusting the cowl flaps such that when in the “closed” position, they’re actually 1” or so cracked open. This small adjustment allows better airflow around the cylinders and reduces CHTs significantly. Don Maxwell did this for me at annual and showed me it has no negative effect on cruise speed. Hope that helps. 

[TigerMooney]

On 8/4/2023 at 11:34 PM, Tx_Aggie said:

I live in western texas. The trick for me was adjusting the cowl flaps such that when in the “closed” position, they’re actually 1” or so cracked open. This small adjustment allows better airflow around the cylinders and reduces CHTs significantly. Don Maxwell did this for me at annual and showed me it has no negative effect on cruise speed. Hope that helps. 

Thanks for that tip. That may be my last option. Had baffling rechecked a second time, fuel injectors cleaned, and had the CHT probes checked….no spark plug gasket plug (same CHT probes all around).

#2 still runs about 20 degrees hotter at times in cruise, while the other 3 are within 5 degrees of each other. 
 

Been uploading my JPI EDM 700 data to savvy analysis pro. They don’t seem alarmed, but it does say I’m in the high end of my cohort for CHTs.