LifeofReiley
Well Known Member
Bob... ++++ 1 But there are good systems making good head way. 
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Van's Air Force
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P-Mag "B" Curve Advance Map
- Thread starter Brantel
- Start date
ColoRv
Well Known Member
What curve are you referring to? You have never seen or discussed Pmags actual curve, just numbers that are part of an equation that calculates that curve. By the way, that's how modern ignitions outside of lycomings have done it for decades.
What I find most funny in this thread is the willingness to take a chart and assumptions made by someone you don't know as gospel, even after a manufacturer whose product directly controls Pmags attempts to explain how the chart is wrong. No wonder manufacturers stay off Internet forums. What purpose would be served by making their curves public? Most of what I've read in here only proves that most wouldn't know how to use that info if they had it. What typically happens is the customer monkeys with things they know naught about and then scream for warranty work when they blow something expensive up. Want proof? Look at post #12.
RVG8tor
Well Known Member
RV10inOz
Well Known Member
Hi Gary
Slight correction to your post above, it is the location of the peak ICP in terms of angle past TDC hence we call it ThetaPP. It is not a contention about the timing lag, it is fact, it happens before your own eyes if you have the ability to measure it. The twist in the crankshaft has a measurable effect, and that too can be measured. But lets ignore that for now as it has no real interest to this discussion.
As for the timing light, yes in theory that is correct, however how good are you at shooting a light, seeing a mark on the flywheel, and then hopefully having a pointer at the right position relative to TDC.
One of the reasons Mags get set up wrong is the old pointer to a mark and rotate the mags. when you use an accurate digital means and I suggest something like a Rite System http://www.ritesystem.net gets good results.
So the timing light may not be the ideal way to do it. What we get on the data set from the dyno is a location of the peak pressure and spark timing and crank angle with something like 50,000 samples per second, or 2500 per revolution. This means for the 60 degrees covering the combustion process (-25 to +35 degrees) has over 400 samples. This is a very good measurement process.
So when you ask about what a timing light is actually telling you, well it will be close I guess.
One point worth raising is that with changes in Mixture, the effective timing of Theta PP varies greatly. The spark timing is still fixed and maybe well advanced. So those who like running at peak EGT or 75ROP are getting a lessor ThetaPP and higher ICP, so best run LOP if you ask me.
Excessive spark advance will reduce HP. How much is excessive?.You get to Guess!
Great question. Lets say, in rough terms the magneto at 20 degrees fires at 13-15 degrees, or assume that a 25dBTDC engine is actually sparking around 18-20 degrees, if you have an accurate electronic device firing at 26 degrees, and there is virtually no lag, or lets assume only a fraction, and then we add to that several more degrees, how far away from the optimal spark timing are we? And how would you know?
Brantel
Well Known Member
Like I told Bill a few post back, my data is straight off the Pmag, matches what EmagAir's EICAD reports, has been verified by Tom the creator and programmer of the Pmag, and matches really close to what numbers are published in the manual.
Bill says his data does not match mine or the published info in the manual, that his data shows that the Pmag's actual timing is somehow different.
I have no way to know which is correct without building a test cell so guys please just take the info for what it is and make up your own mind as to what it means.
The goal in all of this was not to start a war but was to add some additional data for those that want it.
Bill and I are online friends and have been for a long time... I want to keep it that way.... He has a neat product for the Pmag and deserves a ton of credit for bringing it to market.
One thing that I can assure you all of.....nobody knows exacly what is going on inside of the brains of the Pmag other than Tom at EmagAir. Not Brad, not Bill and not Brian.
rocketbob
Well Known Member
Yep I know I've worked on code to do timing advance calculations in C using a multidimensional array, pin capture and timer interrupt...
Even though it became a bit more clear in this thread later on that the numbers being returned serially were not the real advance numbers due to various rounding errors etc., there is ample evidence from the chart that the timing on a PMag is advancing well before the other established ignition manufacturers have done given a particular mid/high power RPM/MP combination.
Brantel
Well Known Member
Interesting timing curve......just sayin
Please tell us where this came from so we don't get it confused with the Pmag.
Weasel
Well Known Member
I have no idea. Sorry if it caused confusion Brantel. I was only ref. it because of how complex they can be vs how simple they can be. It is NOT a pmag chart
Brantel
Well Known Member
No problem, just wanted to clarify for folks that may pop into this thread. This one is definitely complex!
ColoRv
Well Known Member
If you've done what you just said you've done, you know there is no evidence of anything based on that chart. It's part of an equation. It's one variable. That's like saying you can predict HP based on an RPM chart without knowing anything else. I'm not trying to be contentious here, but you are spreading misinformation and people are throwing our things like "Just buy XX instead" based on your misinformation. The chart isn't the curve. It's ONE variable that the curve takes into consideration. That's all.
Brantel
Well Known Member
I don't want to be contentious either but how do we know this is true? Bill says it is but do we just take his word for it? (Sorry Bill)
My stance is that Bill very well may be correct but if Bill is correct, the guys at EMagAir are deceiving all of their customers with their published marketing and technical documentation as well as the tool that they give us to monitor and configure our Pmags.
There public data is either correct or it is not and if it is not, what good is it?
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Perfectly reasonable, assuming they have something to protect...notably the dyno work to establish optimum timing values.
David has told you about determining the point of peak cylinder pressure on the GAMI dyno. I've posted a peak pressure plot taken from FAA dyno work (http://www.vansairforce.com/community/showpost.php?p=838752&postcount=18). Recent work mapping a new electronic ignition for a popular radial was done the same way...recording pressure vs angle vs torque.
So, can anyone tell us how E-Mag developed their map?
Brantel
Well Known Member
Another thing to consider on the theory that they are somehow hiding their true curve...
It does not take too many smarts to find the true curve.
All one needs is:
A variable speed drill motor and handheld tach
A degree wheel
An inductive timing light
A vaccum pump and MAP gauge
It does not take too many smarts to find the true curve.
All one needs is:
A variable speed drill motor and handheld tach
A degree wheel
An inductive timing light
A vaccum pump and MAP gauge
Toobuilder
Well Known Member
It occurs to me reading this thread that we are creating more alarm than discussion. If this was an automotive forum, then the excruciating details of ignition maps would be warranted. After all, an optimized racing engine spends a bunch of time on a dyno changing ignition timing, curve, valve lash, jetting, cam timing, profile, exhaust primary tube length, diameter, configuration and collector... In contrast, we build an engine, run it once and determine its HP...done.
Do I think ignition map data is a useful pursuit? You bet! But really, what are we going to DO with that info? Even most of the aircraft engine gear heads have never done any dyno tuning. It appears they bolt an engine together and simply accept what they get.
So in my mind, we are left with a very simple, "bad" or "good" decision. And the overwhelming evidence points to The PMag product (whatever advance map used) as better than even the best magnetos. Am I happy their advance map is "PFM"?.... No, but I'm also not happy about the nearly nonexistent dyno data for a custom assembled aircraft engine either. It would be nice to do a magazine style "dyno shoot out" among several engine builders to see who can build the strongest Lycoming 360 or 540. But it's unlikely we'll ever see that because the consumer base largely doesn't care.
Do we know exactly what the ignition map of a PMag looks like?
...No
But we DO know it's working better than a magneto.
So perhaps we should keep the end goal in perspective and not freak out 99% of the readers by putting the notion in their head that their engine is going to self destruct the next time they fly. PMags may not be the bleeding edge of ignition timing for every Lycoming ever built, but they are a vast improvement over magnetos. That's one part of their marketing you can believe.
Do I think ignition map data is a useful pursuit? You bet! But really, what are we going to DO with that info? Even most of the aircraft engine gear heads have never done any dyno tuning. It appears they bolt an engine together and simply accept what they get.
So in my mind, we are left with a very simple, "bad" or "good" decision. And the overwhelming evidence points to The PMag product (whatever advance map used) as better than even the best magnetos. Am I happy their advance map is "PFM"?.... No, but I'm also not happy about the nearly nonexistent dyno data for a custom assembled aircraft engine either. It would be nice to do a magazine style "dyno shoot out" among several engine builders to see who can build the strongest Lycoming 360 or 540. But it's unlikely we'll ever see that because the consumer base largely doesn't care.
Do we know exactly what the ignition map of a PMag looks like?
...No
But we DO know it's working better than a magneto.
So perhaps we should keep the end goal in perspective and not freak out 99% of the readers by putting the notion in their head that their engine is going to self destruct the next time they fly. PMags may not be the bleeding edge of ignition timing for every Lycoming ever built, but they are a vast improvement over magnetos. That's one part of their marketing you can believe.
ColoRv
Well Known Member
EmagAir has said from the beginning that they are not releasing their curve which is common in all manufacturing and aftermarket tunes in the performance world. They aren't deceiving anyone. They created a tool to let people control their units, not decipher their proprietary info. You are using the wrong tool for the job you're attempting to do. If you want to KNOW the curve, rent a dyno and do some real testing. A box made on your kitchen table isn't up for the task you are taking on. EmagAir tells you they won't give you their curve but we are to believe that they validated your numbers as their curve? That just doesn't seem likely to me.
Bill tried nicely to explain to you the errors in your assumptions. You continue to get more and more offended. Now you ask if we are going to take Bill at his word? On this topic...yes I am.
rocketbob
Well Known Member
If what you are saying holds true then a EI Commander is doing nothing but spitting out values from the equation, just as Brian has done.
And that would make the product Bill sells worthless. I doubt that being the case.
Other products in this category do not hide this "proprietary" information.
Brian's intention is to see if the ignition is causing CHT issues and he shouldn't have to take his engine off and put it on a dyno to verify a EI maufacturer's RPM/MAP curve. Hence why the other manufacturers provide an interface for one to actively see what is going on.
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rocketbob
Well Known Member
Pretty bold statement!
Is there any test data available to substantiate this claim?
Toobuilder
Well Known Member
I've been directly involved with 3 PMag installations and all 3 airplanes picked up performance immediately. True, my "sample population" is small, but there are plenty of others with substantially similar experience to back up the statement. So much testimony is available in fact that I don't think the debate even exists anymore. EI (and PMags) work better. The only real remaining debate is the cost/benefit due to the fairly steep acquisition costs, and the ongoing "safety" perception of "noncertified" parts. If these ignitions were $400 bucks, they'd be everywhere.
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N941WR
Legacy Member
No worries Brian! You are doing a good, honest thing with your device and posts.
Exactly!
The EICommander does much more than just spit out the raw data as Brian did. The device interprets it and figures out those number's contribution to the timing curve. It also l monitors when the #1 cylinder fires and compares that to the other P-mag and alerts the pilot if there is a significant difference. The data to do that does not come from the streaming data that Brian reported when he initiated this thread. In addition, the EICommander allows you to tune the timing configuration to your needs.
For example, some engines like the IO-390, require timing down around 20* BTC. By simply installing a P-mag and running either the A or B curve, you are doing yourself no favors. You really need to adjust the B curve and dial the timing in as required by your engine manufacture. This can be done via the EICAD program or our EICommander.
In short, no one timing curve fits all engines and it is up to the builder / owner / operator to set the timing that fits their engine.
These engines are not new technology and the timing is well understood. If the P-mags were so bad at firing the sparkplugs, there would be melted engines all over the place.
It is up to you to understand your engine and ignition and match one to the other. There is enough information in the Emag manual to tune the P-mags to fit your needs. The EICommander, besides being an ignition monitoring tool, allows you to make those adjustments.
No rocket science involved in any of this.
Brantel
Well Known Member
Absolutely love the EI benefits of the P-Mag. Starts like a car, so far reliable, runs smooth, cheap plugs, smoother running, I am sure the better fuel burn turns into more power as well.
This thread was not intended to dispute any of those benefits. It was only to understand what the Pmag is doing as it relates to the flurry of post made by David Brown recently along with the call from Dan Horton to use one of the display devices to determine what the Pmag does with its advance. David's postings started sounding more and more like what I was experiencing with CHT's and therefore I wanted to investigate.
Brantel
Well Known Member
For me it is not about how good or bad the Pmag is. I agree however that it is good. I bought and fly behind one each flight. The original intent of this thread was to see how the timing effects my CHT's. Nobody should run away from the Pmag based on this thread.
rocketbob
Well Known Member
That is somewhat alarming as most folks putting these units on don't possess the knowledge to really understand the effects of advance changes. I thought these things were marketed as being brain-dead easy to install.
Brantel
Well Known Member
Please keep in mind that we are all having a friendly debate here. Nothing wrong with that as long as we keep it friendly and civil.
I agree on all but the deceiving part. If their true timing is not what they say it is in the book and as reported by the EmagAir EICAD software, then they are deceiving us. Does this make me furious? Not at all, just cautious when playing around with the settings....
If they did not want people to know what the advance is, why provide the software at all with the ability to monitor it? There own screenshot on their webpage calls describes the meter that monitors advance as "Current Firing Angle". I don't really care what the nuances of their timing curve are. I only want to know that when I make a change to the settings it is going to do what I think it is going to do.
My box is simply a smaller lighter version of EICAD that does not need a laptop to run.
I never said that EmagAir validated my numbers as their curve. What Tom validated was the method that I used to pull the ADV variable out of the ASCII stream and decode it into a number that matches EmagAir's EICAD. My display is actually more accurate since I carry the ADV variable out to 1 decimal place and do not round off the value like EICAD does. I can show you the emails if you want to see them. All I display is the variable as the PMag reports it.
Bill and I are friends, we know how to have a good debate without getting upset. I talked to Bill yesterday for about 30 minutes on the phone. Like I have said in several post Bill very well may be right. I am not in the least offended. I am not passionate enough about this subject to get offended over it.
Like I said above, the original purpose of this thread was only to understand what the Pmag is doing as it relates to the flurry of post made by David Brown recently along with the call from Dan Horton to use one of the display devices (EI Commander, EICAD, Homebrew) to determine what the Pmag does with its advance. David's postings started sounding more and more like what I was experiencing with CHT's and therefore I wanted to investigate.
That being said, I beg you please keep this thread civil and don't turn it into something it is not.
I agree on all but the deceiving part. If their true timing is not what they say it is in the book and as reported by the EmagAir EICAD software, then they are deceiving us. Does this make me furious? Not at all, just cautious when playing around with the settings....
If they did not want people to know what the advance is, why provide the software at all with the ability to monitor it? There own screenshot on their webpage calls describes the meter that monitors advance as "Current Firing Angle". I don't really care what the nuances of their timing curve are. I only want to know that when I make a change to the settings it is going to do what I think it is going to do.
My box is simply a smaller lighter version of EICAD that does not need a laptop to run.
I never said that EmagAir validated my numbers as their curve. What Tom validated was the method that I used to pull the ADV variable out of the ASCII stream and decode it into a number that matches EmagAir's EICAD. My display is actually more accurate since I carry the ADV variable out to 1 decimal place and do not round off the value like EICAD does. I can show you the emails if you want to see them. All I display is the variable as the PMag reports it.
Bill and I are friends, we know how to have a good debate without getting upset. I talked to Bill yesterday for about 30 minutes on the phone. Like I have said in several post Bill very well may be right. I am not in the least offended. I am not passionate enough about this subject to get offended over it.
Like I said above, the original purpose of this thread was only to understand what the Pmag is doing as it relates to the flurry of post made by David Brown recently along with the call from Dan Horton to use one of the display devices (EI Commander, EICAD, Homebrew) to determine what the Pmag does with its advance. David's postings started sounding more and more like what I was experiencing with CHT's and therefore I wanted to investigate.
That being said, I beg you please keep this thread civil and don't turn it into something it is not.
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Brantel
Well Known Member
Today I went to the airport with intentions of mapping the "A" curve as it is presented by the Pmag.
I was able to connect and use EICAD to set the ADV Shift to "0" no problem. This is the same as running with the jumper in or on the "A" curve.
I was incorrect in a prior post when I said my default ADV Shift value was 5.6?, it was actually 4.2? the other defaults that I reported were accurate.
I did fly but it was way too rough to get any data. I did not feel comfortable at the low altitudes running at high power needed to fill in the blanks. It was just too rough.
The data that I did gather however confirms that the Pmag did drop the timing it is reporting by the 4.2? as it should have. The few points I checked were almost exactly my original map -4.2?.
I can tell you however that my CHT's were better on climbout and during high power cruise. The OAT today is about 5?F colder than the last flight but even when you subtract that, the CHT's were much better. I am going to look at the engine data logs and try to give a real number for comparison.
I was able to connect and use EICAD to set the ADV Shift to "0" no problem. This is the same as running with the jumper in or on the "A" curve.
I was incorrect in a prior post when I said my default ADV Shift value was 5.6?, it was actually 4.2? the other defaults that I reported were accurate.
I did fly but it was way too rough to get any data. I did not feel comfortable at the low altitudes running at high power needed to fill in the blanks. It was just too rough.
The data that I did gather however confirms that the Pmag did drop the timing it is reporting by the 4.2? as it should have. The few points I checked were almost exactly my original map -4.2?.
I can tell you however that my CHT's were better on climbout and during high power cruise. The OAT today is about 5?F colder than the last flight but even when you subtract that, the CHT's were much better. I am going to look at the engine data logs and try to give a real number for comparison.
Eh??
Bob, you would not be asking this question if you were in my 4 the other day when i switched the mag off and saw no effect on performance just running on EI. Then when I switched the EI off and just ran on the mag there was an instant drop in power and the EGT's were all over the place.
As a result of that I will be replacing my mag with either a second lightspeed, EF11 system or a Pmag. Having rune EI I never want a magneto again.
What we know about Mags is that they are about as accurate as a broken watch, set up just to ensure that the engine does not melt under any fuel/mixture/rpm, etc condition.
I grew up working on bikes like Vellocettes, Pre Unit Bonnevilles and the like with mags. Even the Harley has EI these days and is a vast improvement on what went before.
Bob, you would not be asking this question if you were in my 4 the other day when i switched the mag off and saw no effect on performance just running on EI. Then when I switched the EI off and just ran on the mag there was an instant drop in power and the EGT's were all over the place.
As a result of that I will be replacing my mag with either a second lightspeed, EF11 system or a Pmag. Having rune EI I never want a magneto again.
What we know about Mags is that they are about as accurate as a broken watch, set up just to ensure that the engine does not melt under any fuel/mixture/rpm, etc condition.
I grew up working on bikes like Vellocettes, Pre Unit Bonnevilles and the like with mags. Even the Harley has EI these days and is a vast improvement on what went before.
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The inconsistencies of the end users experince are a bit puzzling. Although I have very little time on my pmag, the experience of the mag check in the air between my slick and the new pmag was hardly noticeable, 30 RPM drop vs 40 with the slick, every thing else the same. I am running the A curve and auto plug with the pmag
Brantel
Well Known Member
I think it depends on how accurately your Mag is timed along with the Pmag and what RPM/MAP you were at at the time. Keep in mind that the Pmag has variable timing and the Mag does not.
I can tell you that this relationship is very sensitive. My mag check drops changed a bunch just by adding the prop governor to the geartrain that drives the mags.
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Toobuilder
Well Known Member
I don't think you are slamming the PMag product at all, and I think your attempt to "crack the code" is at the heart of every hot rodder/gear head/racer ever born. Good on you!
... But I'd urge some restraint when reporting your somewhat disturbing findings until they are well understood/vetted. And keep in mind the audience here. There are very few who who really know how to use an accurate ignition map in the first place and most of the rest are going to interpret this debate as PMag = bad.
Brantel
Well Known Member
Thats just it, I am not sure what is so disturbing, my data more or less matches what the manual already says just with more detail. I am not qualified to pass judgement on the numbers I posted and have not said they are out of line. I have stated that my own engine reacts like it could stand to go back to the "A" curve or maybe even less advance than the "A" curve which can be done using EICAD.
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Impressive timing!
Don't be fooled by mag checks comparing any EI with a mag, obviously the timing on the two is different. For example the Electro Air/LSE will be running at 39-40 degrees at idle, the Slick/Bendix 20 or 25. That alone is what creates most of the difference that impresses people doing a ground check. If you were to set them the same you would scarcely notice a difference.
In the air same problem, the chance of the mag and the EI firing at the same time is nil, it depends on altitude, throttle setting and rpm, so any comparison is pointless. So if you were to do another mag check at a different Altitude/MP/RPM you might find a much different rpm delta. For example at WOT and 12,000' you will likely not even be able to detect when the magneto is switched off as the EI fired long ago.
Obviously there is value in checking/testing each on the ground and in the air, but the test needs to be done at the same MP/RPM/Mixture to set a base line for future comparison with what each was previously.
Tim
Don't be fooled by mag checks comparing any EI with a mag, obviously the timing on the two is different. For example the Electro Air/LSE will be running at 39-40 degrees at idle, the Slick/Bendix 20 or 25. That alone is what creates most of the difference that impresses people doing a ground check. If you were to set them the same you would scarcely notice a difference.
In the air same problem, the chance of the mag and the EI firing at the same time is nil, it depends on altitude, throttle setting and rpm, so any comparison is pointless. So if you were to do another mag check at a different Altitude/MP/RPM you might find a much different rpm delta. For example at WOT and 12,000' you will likely not even be able to detect when the magneto is switched off as the EI fired long ago.
Obviously there is value in checking/testing each on the ground and in the air, but the test needs to be done at the same MP/RPM/Mixture to set a base line for future comparison with what each was previously.
Tim
AZtailwind
Well Known Member
I'm in agreement with most data presented and the observations- I'm a supporter of the P-Mag and fly behind it. I would not use the B-curve since it lessons the heat margin of a hot CHT climb out -(especially in the summer desert). That may be a different story with an FI engine. I'm carbed.
Now if there is a new "A-B" curve where I'm guaranteed to see default Mag timing (24 deg) at 2700-2550 RPM and 27 and lower-MAP-(all the same dual Mag conservative power points at WOT). I would consider this in the cooler winter months. But that's a wish list along with FI- I'm still want to see where the engine is at with 1000 Hrs on the P-mag. So far all good.
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N941WR
Legacy Member
The problem is the "inconsistencies" in the planes the P-mags are installed on.
Some have cooling issues (Heck, I reduced my CHT's by 20*F just by going after my baffles with RTV!), some have different compression ratios, some even have different head designs. (Ever wonder why one IO-360 is rated at 180 HP and another is rated at 200 HP?)
Like any system we install in our planes, it is up to the builder to read and understand the installation and operation of each component. It is impossible for the manufacture to understand how 500 different builders, with 500 different engines, cooled by 500 different baffle installations will operate their device.
The P-mag manual makes it pretty clear how they need to be installed and configured to match your installation. They do not recommend timing that is outside the requirement of any engine manufacture.
They do go out of their way to provide a tool, the EICAD program, to configure the timing to match your engine.
Heck, if you have forced induction, you can dial the timing in to exactly what your requirements are.
If the P-mag's timing curves were as bad as some of the people on this thread would have you believe, there would be a trail of melted Lycones all over the world.
Kyle Boatright
Well Known Member
Bill, I don't think that's the issue at all. I think the issue is that there are plenty of bright people on this forum who are gearheads at heart. They want to understand the real timing of the P-mag so they can make informed decisions on whether the timing curves are reasonable for their intended use. Without the actual data, everyone has to rely on EmagAir's implied assertion that "The curves are fine. Trust us, the curves are fine. You don't need to know what they are."
In doing that, they are eliminating the possibility of peer review by some very informed individuals.
I understand that and to a great degree, I have been comparing with the "like" engine/setup. Granted they can behave differently under different power settings or operating conditions. So far, I have seen little if any performance gain other than a bit of easier start when cold. I am hoping to see more gains as I log more hours/experience.
Brian?s inspiration...
There are a lot of pertinent questions being presented in this thread. Stepping back a ways I wonder if Brian hasn?t exposed a tacit issue that the electronic ignition folks cannot solve without the engine/big engine-shops input. Our questions and frustration may have to be aimed at a wider audience. Let me explain. Pmags offer the utilitarian ?A? curve and it?s modifiable clone the ?B? curve. Despite the giant leap from dumb mags Pmags are still very limited. The dumb mags must serve every 4 cylinder engine with basically a one size fits all. The Pmag is better but it is still a one size fits all. There is more than anecdotal evidence to show that horsepower, compression ratio, fuel/air mixture, rpm, MAP, fuel (avgas/mogas), mission profile (acro vice cruise) etc are factors in determining your optimum performance. So like Cinderella?s slipper one size doesn?t really fit ?all."
Tell me; who knows better than the engine primes what the maps should be? I?d be really surprised if the EI guys have the deep pockets to develop that data on their own. I know Brad has offered to provide a data collection device to one manufacturer but so far no-joy.
The programmable Pmag is a device to optimize engine performance. The ?engine? guys are going to have to be forthcoming with just what defines optimum performance. Therefore maybe we should also lean on the metal benders to open their kimono to the EI guys.
Inspired by Brian?s Louis and Clark-like mapping quest I went to the web and stumbled upon this clip from a CONTACT! magazine article by Allen W. Cline: ?There is another factor that engineers look for to quantify combustion. It is called "location of peak pressure (LPP)." It is measured by an in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees after top dead center. Depending on the chamber design and the burn rate, if one would initiate the spark at its optimum timing (20 degrees BTDC, for example) the burn would progress through the chamber and reach LPP, or peak pressure at 14 degrees after top dead center. LPP is a mechanical factor just as an engine is a mechanical device. The piston can only go up and down so fast. If you peak the pressure too soon or too late in the cycle, you won't have optimum work. Therefore, LPP is always 14 degrees ATDC for any engine.?
Would an operative question to the ?engine guys? be, ?what ignition map is required to maintain 14 degrees ATDC throughout my operational profile.? And yes, I?m assuming that 14 degrees ATDC is de facto a legitimate holy grail.
There are a lot of pertinent questions being presented in this thread. Stepping back a ways I wonder if Brian hasn?t exposed a tacit issue that the electronic ignition folks cannot solve without the engine/big engine-shops input. Our questions and frustration may have to be aimed at a wider audience. Let me explain. Pmags offer the utilitarian ?A? curve and it?s modifiable clone the ?B? curve. Despite the giant leap from dumb mags Pmags are still very limited. The dumb mags must serve every 4 cylinder engine with basically a one size fits all. The Pmag is better but it is still a one size fits all. There is more than anecdotal evidence to show that horsepower, compression ratio, fuel/air mixture, rpm, MAP, fuel (avgas/mogas), mission profile (acro vice cruise) etc are factors in determining your optimum performance. So like Cinderella?s slipper one size doesn?t really fit ?all."
Tell me; who knows better than the engine primes what the maps should be? I?d be really surprised if the EI guys have the deep pockets to develop that data on their own. I know Brad has offered to provide a data collection device to one manufacturer but so far no-joy.
The programmable Pmag is a device to optimize engine performance. The ?engine? guys are going to have to be forthcoming with just what defines optimum performance. Therefore maybe we should also lean on the metal benders to open their kimono to the EI guys.
Inspired by Brian?s Louis and Clark-like mapping quest I went to the web and stumbled upon this clip from a CONTACT! magazine article by Allen W. Cline: ?There is another factor that engineers look for to quantify combustion. It is called "location of peak pressure (LPP)." It is measured by an in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees after top dead center. Depending on the chamber design and the burn rate, if one would initiate the spark at its optimum timing (20 degrees BTDC, for example) the burn would progress through the chamber and reach LPP, or peak pressure at 14 degrees after top dead center. LPP is a mechanical factor just as an engine is a mechanical device. The piston can only go up and down so fast. If you peak the pressure too soon or too late in the cycle, you won't have optimum work. Therefore, LPP is always 14 degrees ATDC for any engine.?
Would an operative question to the ?engine guys? be, ?what ignition map is required to maintain 14 degrees ATDC throughout my operational profile.? And yes, I?m assuming that 14 degrees ATDC is de facto a legitimate holy grail.
Yes Don, that is exactly the question you should be asking. But first, a question for you....what are you running now? Your signature says you have an IO-390 and dual p-mags. Are you running the A map, the as-delivered B map, or a modified, shifted B-map?
[email protected]
Well Known Member
IO 390 settings...
From within my post (#13)...
After much testing:
IO390
Two P-Mags
Programable curve set to -2.8 degrees
Timed about 2-3 degrees past TDC...
I believe that this gives me an effective floor that works out to something very close to 20 degrees of advance.
From within my post (#13)...
After much testing:
IO390
Two P-Mags
Programable curve set to -2.8 degrees
Timed about 2-3 degrees past TDC...
I believe that this gives me an effective floor that works out to something very close to 20 degrees of advance.
My current configuration is
Hi Dan - Happy New Year,
I am running the A curve now. Frankly the only reason for doing that is lack of courage (read tech savvy) to experiment on my very expensive engine - as you well know. I do plan to follow the lead of more cognizant folks like Brian or Steve (see post just above this one).
Over the next several weeks I'll characterize my "A" curve performance then venture carefully, cautiously to a modified "A" starting with something like Steve did.
Honestly I don't anticipate any great performance enhancements but I think it is worth seeking/finding your engines sweet spot whatever that might be.
Hi Dan - Happy New Year,
I am running the A curve now. Frankly the only reason for doing that is lack of courage (read tech savvy) to experiment on my very expensive engine - as you well know. I do plan to follow the lead of more cognizant folks like Brian or Steve (see post just above this one).
Over the next several weeks I'll characterize my "A" curve performance then venture carefully, cautiously to a modified "A" starting with something like Steve did.
Honestly I don't anticipate any great performance enhancements but I think it is worth seeking/finding your engines sweet spot whatever that might be.
Thanks Don. I asked as an experiment. It appears you're not alone; quite a few folks don't understand the P-mag setup process, or are simply hesitant to work with it. I'm sure the factory attitude is that they wrote adequate instructions and the builders should be able to follow them, but it doesn't seem to be working out that way. Just an observation.
You're running too far advanced. As previously noted, the A map starts around 26 degrees and advances to some unknown figure under unknown circumstances. You need to switch to a modified B map....modified to retard timing as compared to the A map.
Stephen has chosen to retard the map timing by 2.8 degrees and shift the TDC setpoint a few additional degrees. You can also do it by retarding 6 degrees (or more) and blowing in the tube while dead on TDC. Either will work to get your full power timing around 20 degrees BTDC, "correct" for your engine.
Will 20 BTDC timing result in a peak pressure point at 14 ATDC? Not necessarily.
The 20 degree fixed timing is a compromise. There are indeed some conditions where more advance should be beneficial....but there are others where less advance would be the best choice.
As my friend David from Oz has pointed out many, many, many, many times, air-fuel ratio has a significant effect on burn speed. Rich or lean mixtures burn slowly, while mixtures closer to stoichiometric burn faster. The key concept in GAMI training is go lean and use the slower burn rate to delay peak pressure.
Charge density also changes burn rate, lower density being slower. That's why we link variable advance to manifold pressure.
With those things in mind, go back to your fixed, compromise timing of 20 BTDC. If we feed the system a stoich mixture at high manifold pressure, the burn rate is fast and peak pressure arrives early. If we feed it a lean mixture at low density, the burn rate is slow and peak pressure is late. The 20 degree figure wasn't optimum for either end of the spectrum, but it is necessary to cover both ends. In a perfect world you would like less advance for takeoff power and more for high and lean cruise.
I've twice made reference to a peak pressure plot pulled from an FAA study (post 18) in which the subject 540-K has pretty much the same cylinder head as our 390's. Given 20 BTDC timing, high manifold pressure, and a near-stoich mixture the peak pressure is arriving earlier (about 7 ATDC) than the mid-teens optimum (the 14 or so you mentioned previously). By running the 26 degree A map, your peak pressure under the same conditions is even further from optimum, probably near TDC and very high...not a good thing.
RV10inOz
Well Known Member
Indeed Dan
I was reading something from George earlier today about some unrelated testing work he was doing, and at full power in a TN IO550 he had been playing with timing and there was more actual HP at the prop with the timing retarded a bit.
Gets you thinking a little. Besides the observed thetaPP issue, a lower ICP and hence CHT will yield greater volumetric efficiency.
So beside the work in VS work out there are other losses from having the timing too early.
Just little tid bits of information that pop up at times that are useful.
I was reading something from George earlier today about some unrelated testing work he was doing, and at full power in a TN IO550 he had been playing with timing and there was more actual HP at the prop with the timing retarded a bit.
Gets you thinking a little. Besides the observed thetaPP issue, a lower ICP and hence CHT will yield greater volumetric efficiency.
So beside the work in VS work out there are other losses from having the timing too early.
Just little tid bits of information that pop up at times that are useful.
rocketbob
Well Known Member
The K-series 540's have a velocity stack intake tube design that's buried in the sump, so even though the cylinders are stock angle-valve the intake is completely different. Not sure its pertinent to this discussion but worth noting.
Also worth noting is if one is running mogas with a PMag I would be very cognizant about mechanically retarding the timing as others have done here.
Interesting point Bob...theory says higher intake stream velocity should increase turbulence, and thus increase burn rate. That said, is the -K intake tube system really all that much different compared to those used with the 360/390 angle valve horizontal sump? The -K is pretty much just a two-piece version, an internal "extension tube" coupled to an external intake pipe. I'll bet 'ya a Spotted Cow that they're within an inch of the same length overall*
*Heck, I'll buy you one anyway...see you at OSH.
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RV10inOz
Well Known Member
Bob, can I suggest you run that line again in a BIG font size.
N941WR
Legacy Member
Education
There has been a lot comments made about timing. I searched YouTube and found these two videos to help explain what all the concern is about.
While not the best videos, they are worth looking at.
http://www.youtube.com/watch?v=_KEbXwvTxkg
http://www.youtube.com/watch?v=p_P1-2octb4
(There was a better video of an engine firing with a window but I can't find it.)
There has been a lot comments made about timing. I searched YouTube and found these two videos to help explain what all the concern is about.
While not the best videos, they are worth looking at.
http://www.youtube.com/watch?v=_KEbXwvTxkg
http://www.youtube.com/watch?v=p_P1-2octb4
(There was a better video of an engine firing with a window but I can't find it.)
rocketbob
Well Known Member
No on the K engines each tube goes all the way to the opposite side of the sump, and they overlap. The air box side of the sump is two-piece and bolts together, so one can get to everything inside. There is a large magnesium "funnel" casting that holds the RSA-10 in place and directs the air flow to the box. Its sort of a crazy looking setup and quite heavy.
I overhauled one a couple of years ago, hopefully I can dig up a pic of the sump.
I do like Spotted Cow!
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I already did, before betting the beer
See above. The drawings are scaled; compare across the cyl 1 and cyl 2 port ends. Now compare the overall pipe lengths.
rocketbob
Well Known Member
I looked and did not find any photos of the sump, and the parts manual doesn't show a good pic. The Google answer machine revealed nothing either.
You've got the right idea in your enhanced photo but they extend much further, to within 1/2" of the opposite wall on the other side of the sump. When I first saw the arrangement it puzzled me because it violates the general principles of smooth airflow we typically strive for. But then it started making sense to me. Another subject altogether.
Another thought, it would be interesting to validate the A-curve timing and I have a special ignition probe for an oscilloscope to do the job. This would have to be done in-flight One would have to connect a TDC sensor of some sort to the other channel and its simple math to convert the time difference into degrees of rotation at a given RPM.
You've got the right idea in your enhanced photo but they extend much further, to within 1/2" of the opposite wall on the other side of the sump. When I first saw the arrangement it puzzled me because it violates the general principles of smooth airflow we typically strive for. But then it started making sense to me. Another subject altogether.
Another thought, it would be interesting to validate the A-curve timing and I have a special ignition probe for an oscilloscope to do the job. This would have to be done in-flight One would have to connect a TDC sensor of some sort to the other channel and its simple math to convert the time difference into degrees of rotation at a given RPM.
