Q The Engineer Posted November 28, 2022 Report Share Posted November 28, 2022 I wanted to share some info on the M20K engine I've become familiar with. The engine has an intake manifold design that is less than optimum. The standing wave pushes fuel to the rear cylinders causing misfire at low speed, light load. It causes the plugs to load up and misfire. I've flown the airplane training towards my private pilots license so we've run it full rich for about 10 hours. I did a mid field crossing, hit 500 AGL and pulled back to cruise power at 33" in Hg. The engine missed hard enough to shake the plane. My instructor called my airplane to give you an idea. I talked to Bob Minnis as he was the engineer on the J to K project for continental. Bob shared you shouldn't run the engine for that long full rich. I've been leaning the engine out on run up and every 3-4 pattern runs I'll do a run up to lean it out to clean the plugs off. It's worked good so far. FYI Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 28, 2022 Report Share Posted November 28, 2022 Q, Do you use the TIT for mixture control for this type of flight? Cruising around with the fuel flow maxed out is pretty normal for a simple trainer… The NA Long Bodies use a calibrated EGT gauge with a blue/white box for flights like this… The box is a place to operate where the EGT is cool enough for high power production, and hot enough, to keep side effects from occurring… See if Mr. Minnis can give you a box of temperatures for TIT that you can fly with… With the NA engines… the box is about 200°F below peak and is 100° wide… ending about 300°F ROP… Peak TIT is around 1750°F… 1450 to 1550 is a pretty cool place to be… many people don’t exceed 1650°F as a guideline What is your TIT when flying around full rich? MS has a person learning to fly with a TN’d IO550… it’s a twin turbo, high power, engine… His flight instructor, Mike, usually teaches advanced flying techniques in Mooneys…. With thousands of hours of all types of Mooneys… Find a way to operate the engine without having it clog the plugs…. Being too engine friendly, one way… isn’t very engine friendly, going too far that way… This is basic engine management techniques… with an engine monitor, you look up which cylinder stopped firing… if you got a good shake… that is a sign that two plugs in one cylinder… we’re not firing…. The usual next step… the fuel that didn’t burn in the cylinders, shows up in the exhaust and pops loudly as it explodes… (not recommended) Cue the CFI with engine knowledge… When clearing the engine with a run-up… is it always the same plugs showing trouble? Get that engine monitor working for you…! PP thoughts only, not a cfi… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Pinecone Posted November 29, 2022 Report Share Posted November 29, 2022 18 hours ago, carusoam said: Peak TIT is around 1750°F… 1450 to 1550 is a pretty cool place to be… many people don’t exceed 1650°F as a guideline What is your TIT when flying around full rich? AFAIK the peak TIT is is only 1750 for 30 seconds. 1650 continuous. IIRC, the TLS (pre-Bravo) had a 1750 continuous peak TIT, but they were know for issues due to that. I run with a preferred peak of 1600 for engine and turbo longevity. 1 Quote Link to comment Share on other sites More sharing options...
jlunseth Posted November 29, 2022 Report Share Posted November 29, 2022 Just to be on the button, for my 231 the transient TIT redline is 1725 and the continuous is 1650. The numbers may be different for the MB and SB engines in the 252. I believe the induction system in the MB and SB is better but I don’t fly one so not sure. It is true that the induction system in the 231 is just a straight pipe along each side of the engine that starts at the front and dead-ends at a flat plate at the rear end. There are three droppers, one for each cylinder, off that pipe. It would be conducive to a standing wave off that flat plate but that would work in a forward direction driving pressure back up the main log. I do not regularly run the engine full rich, I do that always for the climb but not at cruise speeds. It should be leaned to somewhere around 13.3-14.5 when ROP and around 11 when LOP at cruise. So I don’t question the idea that it is set to run quite rich with the mixture in all the way, but you definitely need that for the climb. Probably just technical, and purely my non-engineer opinion, but don’t think the standing wave drives fuel to the rear cylinders. The fuel is injected at each intake port, it is continuous injection so I am sure fuel briefly builds up there, but to drive the fuel from the forward cylinders to the back cylinders it would have to be evacuated up the length of the dropper, into the main log, and then back the length of the log and then down the dropper for the rearmost cylinder. It would run into the standing wave off the back plate that is pushing pressure back up the main log toward the front. I have GAMIs which are designed to provide a more or less equal mixture to each cylinder. I don’t doubt that without GAMIs the mixtures might be uneven between the cylinders. But I don’t think the theory that fuel is being driven from the intake port of the rear cylinders all the way to the intake of the front cylinders is much of a factor. The issue is just that, to get sufficient fuel to keep the cylinders cool at full power in a climb, the engine must be set up to run quite rich. So to fly at other mixtures and not in a climb it is best to lean the engine out, definitely. I would be concerned if at 33” and full rich the engine shuddered substantially. There is something going on that should not be. My aircraft has not ever done that. Generally, it is very smooth. Another issue is the final approach descent, which is a low power descent. We are taught in pilot school to put the mixture in full rich during that descent just in case we need to go to full power for a go around. However, the engine runs rough and burbles if you do that because it is way overrich. Best to keep the mixture well leaned so the engine runs smooth during that portion of flight. If you need to push to full power for a go around you definitely need to remember to push the mixture in all the way or you will see redline TIT very shortly. 1 Quote Link to comment Share on other sites More sharing options...
Pinecone Posted November 29, 2022 Report Share Posted November 29, 2022 The -MB and -SB are 1750 transient and 1650 continuous. I have a 252 converted to Encore specs. Quote Link to comment Share on other sites More sharing options...
Will.iam Posted November 30, 2022 Report Share Posted November 30, 2022 7 hours ago, Pinecone said: The -MB and -SB are 1750 transient and 1650 continuous. I have a 252 converted to Encore specs. Your 252 turbo is better than mine. I can only go up to 1700 and then only for 30 seconds or less. Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 30, 2022 Report Share Posted November 30, 2022 Gents, When doing short training flights, or cruising to the $100 hamburger Mooney fly-in… How do you select a TIT target… Like any other flight, Just use your allowed continuous operating temp? @Q The Engineer have you see the responses above? Best regards, -a- Quote Link to comment Share on other sites More sharing options...
jlunseth Posted November 30, 2022 Report Share Posted November 30, 2022 I have written about this before as you know Anthony, so repeating myself. I generally use two cruise mixtures, one LOP and one ROP. I am not really setting to TIT, I use TIT to manage my temps once I have my selected mixture put in. My LOP setting is 11.1 GPH/2450 RPM/34” MP. This is 71% power. My ROP mixture is 31”/2450 RPM/at least 13.3GPH. With the LOP mixture I keep the TIT at or below 1600 (continuous is 1650). I suppose I could run hotter but there are two reasons I don’t. One is that I just don’t want to be that hard on the turbo. Two is that my LOP mixture starts to generate too hot temps somewhere around 12-16k in the summer so I must go ROP, and when it does the TIT will creep up. So if the creep happens I want to have room between the 1600 I want to run at and the 1650 redline so I have time to detect and do something about it. If the temps creep up at the higher altitude I go ROP. With the ROP mixture I am watching CHTs, not TIT. If the CHTs start to climb because of OAT the cure is to increase the fuel as high as 14.5 GPH. The TIT while ROP will be lower than the TIT while LOP by quite a bit, around 100 dF, so there is not much reason to be concerned with it while ROP. One the other hand, the CHTs while LOP will be quite a bit cooler, generally, than while ROP so not much reason to be concerned with those, the temp to watch is TIT. My approach setting is 24.5 MP/2450 RPM/8.8 GPH. I use this to fly holds, instrument approaches, and on downwind in the pattern, or any other time I am not in need of full cruise speed. This is a LOP setting. In reality I target airspeed, I want my approach speed to be 120 kts. With gear down it is slower, around 90-100. The MP and fuel flow may need to be a little higher on some days, say in the middle of the summer, up as high as 25.5 and about 8.9 GPH. On final I keep the engine leaned out to stop the burble. The burble is the engine missing or making little power on some cylinder strokes, because of excessive fuel. You can hear when you have it leaned far enough, the engine should run smoothly. These settings may be a little high. Mine engine is old, way past TBO, we are waiting on a new one. In a turbo I can make up for lost HP because of engine age, with higher power settings. When I get the new engine I am going to have to revisit the whole thing. Quote Link to comment Share on other sites More sharing options...
Pinecone Posted November 30, 2022 Report Share Posted November 30, 2022 7 hours ago, Will.iam said: Your 252 turbo is better than mine. I can only go up to 1700 and then only for 30 seconds or less. I will double check when I get home. Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted November 30, 2022 Report Share Posted November 30, 2022 I believe you guys are missing the issue, Mooney’s weren’t designed nor intended to be used by and flown by Student pilots to get their license, especially the more complex turbo ones. They just aren’t pattern, touch and go type, slow flight type of airplane. There are entire fleets of airplanes that are. They are traveling machines. Way back when I worked as an auto mechanic, a local Dr had a very specially prepped 911, motor was built by a race shop in Atl. He would bring it to me as no one else could “tune it up” as well as I could, all I did was clean the plugs and go out and run it through the gears a few times at full throttle coming close to red line. He would take it back and drive it back and forth in traffic to the hospital, maybe out to eat a few times a week, in a month or so he would be back. His issues will go away once the aircraft is used as designed and intended. How much wear and damage will it accumulate until then? Who knows, but the hours its being flown as a trainer are equal to many more hours of cruise 1 Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 On 11/28/2022 at 12:44 PM, carusoam said: Q, Do you use the TIT for mixture control for this type of flight? Cruising around with the fuel flow maxed out is pretty normal for a simple trainer… The NA Long Bodies use a calibrated EGT gauge with a blue/white box for flights like this… The box is a place to operate where the EGT is cool enough for high power production, and hot enough, to keep side effects from occurring… See if Mr. Minnis can give you a box of temperatures for TIT that you can fly with… With the NA engines… the box is about 200°F below peak and is 100° wide… ending about 300°F ROP… Peak TIT is around 1750°F… 1450 to 1550 is a pretty cool place to be… many people don’t exceed 1650°F as a guideline What is your TIT when flying around full rich? MS has a person learning to fly with a TN’d IO550… it’s a twin turbo, high power, engine… His flight instructor, Mike, usually teaches advanced flying techniques in Mooneys…. With thousands of hours of all types of Mooneys… Find a way to operate the engine without having it clog the plugs…. Being too engine friendly, one way… isn’t very engine friendly, going too far that way… This is basic engine management techniques… with an engine monitor, you look up which cylinder stopped firing… if you got a good shake… that is a sign that two plugs in one cylinder… we’re not firing…. The usual next step… the fuel that didn’t burn in the cylinders, shows up in the exhaust and pops loudly as it explodes… (not recommended) Cue the CFI with engine knowledge… When clearing the engine with a run-up… is it always the same plugs showing trouble? Get that engine monitor working for you…! PP thoughts only, not a cfi… Best regards, -a- Great post, thanks for your feedback. I've not been using TIT to tune for a couple of reasons, my instructor is not good with anything not full rich until reaching pattern altitude and that coupled with me not being that good yet keeps me at full rich. I'll add the TIT tuning when everything is automatic, it's clearly not yet. I'll ask Bob about the box numbers and check the POH. Running the engine lean of peak on the run up and doing a run up lean every 3 pattern runs has solved the problem so far as Bob suggested. I wouldn't want to go 1650 deg F even with an inconel turbine/casing. No engine monitor here other than TIT, CDT, oil temp and head temp as from Mooney. We definitely got shake but no bang so it must not have been too bad. I can't tell you if it's the same plugs or not without exh port temp measurements. Bob's thought was full rich with extended rich idle times and the poor intake design on the MB loading the back cylinders is causing the issue. I've been helping my CFI with the engine management but I'm still learning stuff. I've been doing engine development/design for 32 years so I get the fundamentals. Good thoughts sir, thanks for your feedback. 1 Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 On 11/29/2022 at 7:21 AM, Pinecone said: AFAIK the peak TIT is is only 1750 for 30 seconds. 1650 continuous. IIRC, the TLS (pre-Bravo) had a 1750 continuous peak TIT, but they were know for issues due to that. I run with a preferred peak of 1600 for engine and turbo longevity. I'm with you on the TIT, I'm thinking 1650 deg F for continuous is a bit high. I'll check with my guys for a check on TIT limits using inconel. Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 19 hours ago, jlunseth said: Just to be on the button, for my 231 the transient TIT redline is 1725 and the continuous is 1650. The numbers may be different for the MB and SB engines in the 252. I believe the induction system in the MB and SB is better but I don’t fly one so not sure. It is true that the induction system in the 231 is just a straight pipe along each side of the engine that starts at the front and dead-ends at a flat plate at the rear end. There are three droppers, one for each cylinder, off that pipe. It would be conducive to a standing wave off that flat plate but that would work in a forward direction driving pressure back up the main log. I do not regularly run the engine full rich, I do that always for the climb but not at cruise speeds. It should be leaned to somewhere around 13.3-14.5 when ROP and around 11 when LOP at cruise. So I don’t question the idea that it is set to run quite rich with the mixture in all the way, but you definitely need that for the climb. Probably just technical, and purely my non-engineer opinion, but don’t think the standing wave drives fuel to the rear cylinders. The fuel is injected at each intake port, it is continuous injection so I am sure fuel briefly builds up there, but to drive the fuel from the forward cylinders to the back cylinders it would have to be evacuated up the length of the dropper, into the main log, and then back the length of the log and then down the dropper for the rearmost cylinder. It would run into the standing wave off the back plate that is pushing pressure back up the main log toward the front. I have GAMIs which are designed to provide a more or less equal mixture to each cylinder. I don’t doubt that without GAMIs the mixtures might be uneven between the cylinders. But I don’t think the theory that fuel is being driven from the intake port of the rear cylinders all the way to the intake of the front cylinders is much of a factor. The issue is just that, to get sufficient fuel to keep the cylinders cool at full power in a climb, the engine must be set up to run quite rich. So to fly at other mixtures and not in a climb it is best to lean the engine out, definitely. I would be concerned if at 33” and full rich the engine shuddered substantially. There is something going on that should not be. My aircraft has not ever done that. Generally, it is very smooth. Another issue is the final approach descent, which is a low power descent. We are taught in pilot school to put the mixture in full rich during that descent just in case we need to go to full power for a go around. However, the engine runs rough and burbles if you do that because it is way overrich. Best to keep the mixture well leaned so the engine runs smooth during that portion of flight. If you need to push to full power for a go around you definitely need to remember to push the mixture in all the way or you will see redline TIT very shortly. I checked the 252 POH Bob gave me. Normal is 1300-1650 deg F, 1650 deg F redline maximum limit*. * = do not exceed 1650 deg F for more than 30 seconds, do not exceed 1700 deg F under any circumstance. Yep the GB and LB's have a short runner to the head with a long log. The MB and SB's have a tuned, longer runner. MB and SB's also have a Garret turbo and an aftercooler where the GB/LB doesn't, it's a straight turbo, no aftercooler. On the short drop runner GB and LB's, the standing wave under lower speed conditions pushes injected fuel back into the long log. The air is fed front to back on the engine so as air is moved to feed the middle and back cylinders the mixture gets richer and richer causing over rich conditions on the back cylinders. The MB and SB intake runners are 4x longer than the GB/LB (haven't measured my parts yet, much longer) so the standing wave pushes the injected fuel up the runner the same amount however, since the runner is much longer, the blown back fuel never hits the common log/plenum so the fuel doesn't get pushed to the middle and back cylinders. That is the idea in theory. Bob says he proved it during 231 development which is what drove the new intake manifold on the 252. He sent me the data but I haven't had a chance to look at it yet. What are you referencing on 13.3-14.5 when Rich Of Peak and around 11 on Lean Of Peak? That is new to me. The burble on decent is definitely there! I'm not ready for TIT tuning in the pattern yet, I'm not that good. And I kinda like the burble being a race car guy. Thanks for your feedback. Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 10 hours ago, carusoam said: Gents, When doing short training flights, or cruising to the $100 hamburger Mooney fly-in… How do you select a TIT target… Like any other flight, Just use your allowed continuous operating temp? @Q The Engineer have you see the responses above? Best regards, -a- Just getting caught up, thanks for your feedback. If you're looking for best fuel economy, yes, max allowed continuous TIT should do it. Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 2 hours ago, jlunseth said: I have written about this before as you know Anthony, so repeating myself. I generally use two cruise mixtures, one LOP and one ROP. I am not really setting to TIT, I use TIT to manage my temps once I have my selected mixture put in. My LOP setting is 11.1 GPH/2450 RPM/34” MP. This is 71% power. My ROP mixture is 31”/2450 RPM/at least 13.3GPH. With the LOP mixture I keep the TIT at or below 1600 (continuous is 1650). I suppose I could run hotter but there are two reasons I don’t. One is that I just don’t want to be that hard on the turbo. Two is that my LOP mixture starts to generate too hot temps somewhere around 12-16k in the summer so I must go ROP, and when it does the TIT will creep up. So if the creep happens I want to have room between the 1600 I want to run at and the 1650 redline so I have time to detect and do something about it. If the temps creep up at the higher altitude I go ROP. With the ROP mixture I am watching CHTs, not TIT. If the CHTs start to climb because of OAT the cure is to increase the fuel as high as 14.5 GPH. The TIT while ROP will be lower than the TIT while LOP by quite a bit, around 100 dF, so there is not much reason to be concerned with it while ROP. One the other hand, the CHTs while LOP will be quite a bit cooler, generally, than while ROP so not much reason to be concerned with those, the temp to watch is TIT. My approach setting is 24.5 MP/2450 RPM/8.8 GPH. I use this to fly holds, instrument approaches, and on downwind in the pattern, or any other time I am not in need of full cruise speed. This is a LOP setting. In reality I target airspeed, I want my approach speed to be 120 kts. With gear down it is slower, around 90-100. The MP and fuel flow may need to be a little higher on some days, say in the middle of the summer, up as high as 25.5 and about 8.9 GPH. On final I keep the engine leaned out to stop the burble. The burble is the engine missing or making little power on some cylinder strokes, because of excessive fuel. You can hear when you have it leaned far enough, the engine should run smoothly. These settings may be a little high. Mine engine is old, way past TBO, we are waiting on a new one. In a turbo I can make up for lost HP because of engine age, with higher power settings. When I get the new engine I am going to have to revisit the whole thing. Good post and the numbers are fuel flow for ROP and LOP. Thanks and cancel my request. Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 58 minutes ago, A64Pilot said: I believe you guys are missing the issue, Mooney’s weren’t designed nor intended to be used by and flown by Student pilots to get their license, especially the more complex turbo ones. They just aren’t pattern, touch and go type, slow flight type of airplane. There are entire fleets of airplanes that are. They are traveling machines. Way back when I worked as an auto mechanic, a local Dr had a very specially prepped 911, motor was built by a race shop in Atl. He would bring it to me as no one else could “tune it up” as well as I could, all I did was clean the plugs and go out and run it through the gears a few times at full throttle coming close to red line. He would take it back and drive it back and forth in traffic to the hospital, maybe out to eat a few times a week, in a month or so he would be back. His issues will go away once the aircraft is used as designed and intended. How much wear and damage will it accumulate until then? Who knows, but the hours its being flown as a trainer are equal to many more hours of cruise I'm learning in mine so I'll deal with the consequences. I just don't see training in a 172 for 70 hours that I'm never going to fly again. They are traveling machines for sure. It sounds like the race shop had the A/F ratio way rich causing the issue. It was common on engines with high overlap cams. It takes a bit of carb work but it can be resolved, you just need more airflow at idle without feeding it more fuel. I understand and will deal with it. Fuel dilution is fine, the biggest issue is fouling the plugs. It shouldn't be too much of a problem as long as it gets leaned out to clean the plugs up frequently. Thanks for the feedback. Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted November 30, 2022 Author Report Share Posted November 30, 2022 FYI, our TIT limit with inconel turbines/housings is 1562 deg F continuous. I don't believe any better production materials were available back in the 80's to mid 90's for turbines. Our TBO expectations are 20,000 hours using that TIT limit. Quote Link to comment Share on other sites More sharing options...
jlunseth Posted November 30, 2022 Report Share Posted November 30, 2022 @Q That is good information about the standing wave. If Bob says he proved it, he did. The issue I have always wondered about in a non-tuned exhaust like the GB/LB is whether the successive cylinders along the log (my word for the main runner) receive the same MP. We have measured MP at the start of the intake, of course, let's just say its 30" for the sake of discussion, but whether it is 30" at each of the cylinders down the log is another question. I have reason to believe that at near idle it is not. The last two cylinders on each side do not "come alive" and start producing power until the engine is warm and powered up a little. The cylinders upstream seem to be stealing all the air. It is entirely possible that MPs vary not only along the log, but also vary differently depending on the measured MP. So at, say, 14", not much pressure gets to the last cylinders because it is being stolen by the first cylinders, while at, say, 36" there may be so much pressure in the log that it evens out to all the cylinders, and at measured pressures in between it may be mixed results. There are also no doubt standing waves produced in multiple directions along the log and the position of the wave fronts probably varies with measured MP. GAMIs (which I have) operate on a sort of "all other things being equal" basis. In other words, one runs a lean test at a certain MP, installs GAMIs that even out the fuel flows for each cylinder, and the thesis is that if the MP changes from the MP used for the test, it affects all cylinders more or less equally and therefore the GAMI's continue to provide the proper fuel flow to each cylinder to make the mixtures more or less the same. But what if the pressures at each cylinder intake do not increase or decrease equally with increases and decreases in measured MP, what if the wave fronts change, what if at high pressures relatively more air gets to the back cylinders than at low pressures, etc. This is all theoretical. My engine (Merlin and intercooled LB) runs well LOP at all power settings. But I have often wondered what is going on inside that untuned manifold. Beyond my instrumentation. Quote Link to comment Share on other sites More sharing options...
carusoam Posted December 1, 2022 Report Share Posted December 1, 2022 Q, How soon can you get an engine monitor? It must be killing you to not have the usual plethora of data…. Some of the best writing on engine ops of the M20K… found around here… Come from @jlunseth…. Where he has detailed the practical procedures of flying LOP with his M20K… A few pages over time…. The search function will probably be able to hunt down those discussions… See if you can find a TIT between too rich, and too hot… Fortunately, you are familiar with turbo temp issues already… You probably want to lean enough to not foul the plugs… It is OK to clear them out every now and then… But that sets you up for missing an important problem if it is happening at the same time…. If you have an internal oil leak… it will also be masked by clearing the plugs… Turbos often go 1k hrs before they see any maintenance… where seals get changed… if a seal wears abnormally, it may leak oil into the intake… PP casual conversation only… no turbos on my IO550, yet… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Aerodon Posted December 2, 2022 Report Share Posted December 2, 2022 I think you are over thinking this. First, get a set of GAMi's, your engine will run better and they are easy to fit during an oil change. Second, get a 6 cylinder engine monitor with fuel flow. Third make sure your engine fuel pump is properly setup according to the Continental SB. A good mechanic will be able to use the engine monitor and tell you if everything is more or less right without doing this SB. Fourth, get a new CFI, if he can't teach you how to manage the engine, what else is he not teaching you? I think you are off the mark speculating about a standing wave. Prior to GAMi, the belief was that there was an imbalance in airflow to the middle and aft cylinders. Continental spent millions fixing it with the MB engines. After GAMi's came along, it is well understood that with continuous flow injectors, when the front intake valve is closed, the fuel is injected into the stationary air, evaporates, expands and some is carried backwards. It is a very precise amount, and very repeatable, solved by a set of off the shelf GAMi injectors. Aerodon 1 Quote Link to comment Share on other sites More sharing options...
Will.iam Posted December 2, 2022 Report Share Posted December 2, 2022 16 minutes ago, Aerodon said: I think you are over thinking this. First, get a set of GAMi's, your engine will run better and they are easy to fit during an oil change. Second, get a 6 cylinder engine monitor with fuel flow. Third make sure your engine fuel pump is properly setup according to the Continental SB. A good mechanic will be able to use the engine monitor and tell you if everything is more or less right without doing this SB. Fourth, get a new CFI, if he can't teach you how to manage the engine, what else is he not teaching you? I think you are off the mark speculating about a standing wave. Prior to GAMi, the belief was that there was an imbalance in airflow to the middle and aft cylinders. Continental spent millions fixing it with the MB engines. After GAMi's came along, it is well understood that with continuous flow injectors, when the front intake valve is closed, the fuel is injected into the stationary air, evaporates, expands and some is carried backwards. It is a very precise amount, and very repeatable, solved by a set of off the shelf GAMi injectors. Aerodon I agree with the list but it’s backwards to the implementation. Make sure the fuel system is setup properly first then get an engine monitor with fuel flow to identify which cylinder(s) are leaner than the average and which are richer than the average. One of the first things gami wants is a data file of the lean test sweep to identify which cylinder peaks at what fuel flow so as to finely tune the injectors to each cylinder. If not you could be wasting your time as well as theirs with swapping out injectors that are miss matched. Also fix any induction leaks before ordering or you will be getting an injector tuned to the leak and once fixed will have to swap that injector out with a richer one once none of the air is escaping out the leak. Quote Link to comment Share on other sites More sharing options...
Aerodon Posted December 2, 2022 Report Share Posted December 2, 2022 Just now, Will.iam said: I agree with the list but it’s backwards to the implementation. Make sure the fuel system is setup properly first then get an engine monitor with fuel flow to identify which cylinder(s) are leaner than the average and which are richer than the average. One of the first things gami wants is a data file of the lean test sweep to identify which cylinder peaks at what fuel flow so as to finely tune the injectors to each cylinder. If not you could be wasting your time as well as theirs with swapping out injectors that are miss matched. Also fix any induction leaks before ordering or you will be getting an injector tuned to the leak and once fixed will have to swap that injector out with a richer one once none of the air is escaping out the leak. I disagree, GAMi does not need a set of data, I have installed 4 sets of GAMI's in TSIO360's and all had excellent results out of the box. GAMi will start fine tuning if you are not getting good results after installing. (Yes, if you have a MB or SB engine you need data first). The priority is to get a good set of injectors in, so you more or less eliminate that variable. Also you would not want to have to repeat the fuel setup process again after installing the GAMis would you? It's a fairly time consuming process, I would guess a few hours at least. The reason I say engine monitor second, is you know you are going to install one eventually, so do it early to be able to do the GAMi test and also gain knowledge on how your engine is running. I know the Continental SB, and it is supposed to be done every year (especially if you need to maintain a cylinder or engine warranty). But if you have a lot of data, you will know if you need to make any adjustments. This test was invented before the advent of 6 cylinder engine monitors and before GAMi's etc. When my engines are running fine, I'm not about to go through the whole setup again just to feel better. Aerodon Quote Link to comment Share on other sites More sharing options...
T. Peterson Posted December 3, 2022 Report Share Posted December 3, 2022 On 11/30/2022 at 7:01 AM, jlunseth said: I have written about this before as you know Anthony, so repeating myself. I generally use two cruise mixtures, one LOP and one ROP. I am not really setting to TIT, I use TIT to manage my temps once I have my selected mixture put in. My LOP setting is 11.1 GPH/2450 RPM/34” MP. This is 71% power. My ROP mixture is 31”/2450 RPM/at least 13.3GPH. With the LOP mixture I keep the TIT at or below 1600 (continuous is 1650). I suppose I could run hotter but there are two reasons I don’t. One is that I just don’t want to be that hard on the turbo. Two is that my LOP mixture starts to generate too hot temps somewhere around 12-16k in the summer so I must go ROP, and when it does the TIT will creep up. So if the creep happens I want to have room between the 1600 I want to run at and the 1650 redline so I have time to detect and do something about it. If the temps creep up at the higher altitude I go ROP. With the ROP mixture I am watching CHTs, not TIT. If the CHTs start to climb because of OAT the cure is to increase the fuel as high as 14.5 GPH. The TIT while ROP will be lower than the TIT while LOP by quite a bit, around 100 dF, so there is not much reason to be concerned with it while ROP. One the other hand, the CHTs while LOP will be quite a bit cooler, generally, than while ROP so not much reason to be concerned with those, the temp to watch is TIT. My approach setting is 24.5 MP/2450 RPM/8.8 GPH. I use this to fly holds, instrument approaches, and on downwind in the pattern, or any other time I am not in need of full cruise speed. This is a LOP setting. In reality I target airspeed, I want my approach speed to be 120 kts. With gear down it is slower, around 90-100. The MP and fuel flow may need to be a little higher on some days, say in the middle of the summer, up as high as 25.5 and about 8.9 GPH. On final I keep the engine leaned out to stop the burble. The burble is the engine missing or making little power on some cylinder strokes, because of excessive fuel. You can hear when you have it leaned far enough, the engine should run smoothly. These settings may be a little high. Mine engine is old, way past TBO, we are waiting on a new one. In a turbo I can make up for lost HP because of engine age, with higher power settings. When I get the new engine I am going to have to revisit the whole thing. Thank you for repeating yourself. I found it very helpful. As a matter of fact I am going to screenshot and print this page. Thanks again, Torrey Quote Link to comment Share on other sites More sharing options...
Q The Engineer Posted December 3, 2022 Author Report Share Posted December 3, 2022 On 11/30/2022 at 12:33 PM, jlunseth said: @Q That is good information about the standing wave. If Bob says he proved it, he did. The issue I have always wondered about in a non-tuned exhaust like the GB/LB is whether the successive cylinders along the log (my word for the main runner) receive the same MP. We have measured MP at the start of the intake, of course, let's just say its 30" for the sake of discussion, but whether it is 30" at each of the cylinders down the log is another question. I have reason to believe that at near idle it is not. The last two cylinders on each side do not "come alive" and start producing power until the engine is warm and powered up a little. The cylinders upstream seem to be stealing all the air. It is entirely possible that MPs vary not only along the log, but also vary differently depending on the measured MP. So at, say, 14", not much pressure gets to the last cylinders because it is being stolen by the first cylinders, while at, say, 36" there may be so much pressure in the log that it evens out to all the cylinders, and at measured pressures in between it may be mixed results. There are also no doubt standing waves produced in multiple directions along the log and the position of the wave fronts probably varies with measured MP. GAMIs (which I have) operate on a sort of "all other things being equal" basis. In other words, one runs a lean test at a certain MP, installs GAMIs that even out the fuel flows for each cylinder, and the thesis is that if the MP changes from the MP used for the test, it affects all cylinders more or less equally and therefore the GAMI's continue to provide the proper fuel flow to each cylinder to make the mixtures more or less the same. But what if the pressures at each cylinder intake do not increase or decrease equally with increases and decreases in measured MP, what if the wave fronts change, what if at high pressures relatively more air gets to the back cylinders than at low pressures, etc. This is all theoretical. My engine (Merlin and intercooled LB) runs well LOP at all power settings. But I have often wondered what is going on inside that untuned manifold. Beyond my instrumentation. The tuned exhaust is only used if the cam is set up for it. You need the low pressure wave hitting the cylinder when both the intake and exhaust valves are open using the exhaust energy to pull in air from the intake on overlap. I think you're talking average pressure versus dynamic pressures in both systems. The average is the average, the dynamic is the result of blow down and tuning lengths on both the intake and exhaust. I have no idea what a GAMI is? Can you share some info? It sounds like you have a great machine! Cheers! Quote Link to comment Share on other sites More sharing options...
jlunseth Posted December 3, 2022 Report Share Posted December 3, 2022 GAMI is General Aviation Modifications Inc. They sell tuned injectors. https://gami.com. One runs a lean test that is described on GAMI’s website. The idea is to determine at what fuel flows each factory injector causes its cylinder to hit peak EGT. With that information, GAMI sells you a set of injectors that brings the range of fuel flows at which peak is reached to within 0.5 GPH or less. This helps the engine run more smoothly. It also is very helpful if you want to operate your engine lean of peak. Quote Link to comment Share on other sites More sharing options...
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