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E/Pmag timing advance explained

N941WR

Legacy Member
We have had a number of customers ask about the E/Pmag timing advance and how it works. I thought it might be worth posting our reply on here so that other Emag customers might benefit.

E/Pmag Electronic Ignition

The E/Pmag controls the ignition timing through a combination of:
1. Static timing of the E/Pmags set mechanically to approx 25 Deg (for typical Lycoming 4 cylinder)
2. Advance Curve Selected (e.g. Via the "A" or "B" configuration - or user configuration, if using the Laptop EICAD program or the Electronic Ignition Commander. The “B” curve is the only configurable curve and can be adjust as the user sees fit. The EICommander[/url’] stores multiple configurations and when sent to the E/Pmas updates the “B” configuration memory location.)
3. Amount of RPM and Manifold Pressure sensed

Typically, the E/Pmag static timing is mechanically set to around 20 deg BTDC using the Pmag set up procedures (blow in the tube or by turning the E/Pmags). A base table is then used to relate the rpm/manifold pressure values to the advance curve selected to provide the timing advance increase. So total advance = Static (25 deg BTDC) + advance value (function of RPM/Manifold pressure). The "A" advance curve is shown in orange line in the graph below. More aggressive advance curves are indicated in blue and less aggressive in Green. Note that if a very aggressive advance curve is configured and sent to the E/Pmags, you will hit the 39 Deg Max Angle shown at a lower RPM value.



The default factor advance curve is set by the "A" configuration which has a constellation shift of zero deg. This means the constellation shift = 0.0 which results in the active advance curve being the default "A" configuration curve. If the "B" curve is selected, then the advance curve is biased 5 deg in front(ahead of) the "A" curve as shown by the blue line in the drawing. So this is a more aggressive ignition advance as it will have approximately a five (5) degree timing advance over the “A” configuration at each rpm/manifold pressure point along the curve.

In either case as RPM/Manifold pressure changes this causes the total ignition advance to vary. Total Advance = Static Timing (20 Deg BTDC) + Amount of advance as a function of RPM/Manifold Pressure.

If you are using your Laptop and the Emag EICAD program provided from Emag’s web site or the EICommander to monitor, control or change your E/Pmag ignition configuration, there are a total of four ignition advance values affecting ignition timing. Two are static (limit) settings and two are dynamic values. All four items are reported over the E/Pmag serial communication link.

Static Advance Settings (These values can be adjusted with Laptop or EICommander)
1. Advance Maximum - This is the total ignition advance limit set by the configuration of the Pmag. Once and if this limit is reached, the Pmag will not advance the ignition timing beyond this value
2. Constellation Shift - This sets the aggressiveness of the advance curve. "A" is the default with constellation shift set = 0.0. "B" provides slightly more aggressive advance curve of being 5 degrees more advanced at each RPM/Manifold point than the "A" curve. The E/Pmag permits a maximum of +12.6 degree of “shift” - a very aggressive advance profile (negative values are also permitted, which might be desired for forced induction engines [turbo or super charging]).

These two settings place limits on maximum advance permitted and how aggressive the curve to that maximum advance will be. With a "B" curve for example the E/Pmag could reach the same point at a lower rpm/manifold pressure point than the "A" curve, so the ignition could run into the Maximum Advance limit at a lower rpm for example - unless the user adjusted the Maximum Advance Limit upward. Also the Maximum RPM limit for the E/Pmag may need to be increased to accommodate the more aggressive advance curve.

Dynamic Advance Values (These values are reported on the serial link by the E/Pmag)
1. Target Advance - exists and is reported over serial link, but not currently used nor displayed by the EICAD program or the EICommander.
2. Current Advance - this is the firing point of the E/Pmag - This is the total advance, which is a combination of the static timing point plus the timing advance based on the advance curve selected (A or B or user) and the point on that curve as a function of RPM/Manifold pressure.
 
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Emag

Thanks Bill,
This very subject has been on my mind for the past few days.
Apparently, you have ESPN.

Thanks for posting.
And BTW, how is your RV9 rebuild coming along??

Regards, Chris
 
...
Apparently, you have ESPN.

Thanks for posting.
And BTW, how is your RV9 rebuild coming along??

Regards, Chris

No ESPN, I want to work on the plane, not watch TV.

The -9 is getting close. I'm sitting on the basement steps right now getting ready to update some new beta code to the EICommander. While that is running I'm doing some of the engine's finish wiring. It is oh so close to moving back to the airport.

Feel free to hit me up with any questions regarding the E/P-mags. For some reason I've learned how they work fairly well.
 
So how does one determine if they should remove the jumper? Is there a downside or concern. Currently I only have the MAP hooked up but jumpers still installed.
 
So how does one determine if they should remove the jumper? Is there a downside or concern. Currently I only have the MAP hooked up but jumpers still installed.
Tony,

That is a good question and one that each pilot/owner/operator will have to make on their own.

What I would suggest doing is to connect a PC to each E/P-mag and change the advance to half its current value and split the difference on the max advance between the A and B curves. Go fly it the plane and watch your CHT and EGT's. If all is good, then bump them up again to the full B curve.

Remember, as you change the advance, you will see your CHTs go up and your EGTs go down as you are burning more in your cylinders and there is less fire to go out past the exhaust valve.

Back when I first installed the dual Pmags I simply moved to the full B curve after 20 hours and never looked back. Well, that was until we developed the EICommander.
 
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what do pmag jumpers do?

So how does one determine if they should remove the jumper? Is there a downside or concern. Currently I only have the MAP hooked up but jumpers still installed.
What do the jumpers do? They aren't described in the excellent writeup above.
 
Dave,

Just to be clear, there is really only one timing curve in the EPI (E/Pmag Ignitions). The "A curve" starts at ~26 degrees BTC and has a max advance of 33.6 degrees. The "B curve" is programmable by the user but the factory default shifts the standard curve an additional 4.2 degrees and caps the max advance at 37.8 degrees over the "A" configuration.

If you put a jumper between terminals #2 and #3 on the EPI, you force them to use configuration "A". Without the jumper, they run the more advanced configuration "B".

Due to how the EPI's are programmed, you can shift the entire curve left or right of the standard "A" curve.

When using the EICommander you remove the jumper and the EICommander sends all the configuration information to the "B" curve. Thus if you are using our device and select the "A" curve, we load the default "A" curve info into the "B" memory area. Same goes with the multiple configurations the EICommander can store locally, when you select a custom configuration, it will move that from the EICommander and place it in the "B" curve memory location.

What I was suggesting to Tony was to modify the "B" configuration by reducing the total shift from 4.2 to 2.8 and set the Max advance at either 36.4 or 35.0. (The EPIs are programed in such a way that you must adjust the timing sifts in jumps of 1.4.)
 
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RPM Limits

The EPI's do have a rev limiter which will stop firing the spark plugs when you hit it.

The default value for both the "A" and "B" curves is 3072.

The rev limiter can be raised and lowered in the following increments: 3072, 2816, & 2560.

Why is it there if you can't set it at your redline? Well, aircraft engines can run over redline and it is there to save your engine if you have a problem, such a CS prop's governor goes "wonky", it will keep your engine from grenading. These pre-defined values are a feature of the EPIs and not the EICommander, just to be clear.

I would not want to hit the rev limiter in a large displacement four cylinder aviation engine. In fact, we have not tested it as we do want to fly behind our engines; however, the Emag guys have tested it and they assure me it works.

(While auto racing I often hit the rev limiter in my car and on occasion ran on the limiter rather than shifting. As I said, I'm not so sure I want to see what happens to our large displacement four cylinder engines when they bump against a hard rev limiter.)
 
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I am thinking about running some MOGAS in the near future. It seems to be that the "Restricted" "B" curve might be better (Jumper installed)?

What are the advantages of using the full "B" curve? I assume better combustion, therefore more power and economy? At some point can you go to far with the advance and start getting in to danger?
 
I am thinking about running some MOGAS in the near future. It seems to be that the "Restricted" "B" curve might be better (Jumper installed)?
The jumper forces the EPIs to run on the "A" curve. If you want to run the "B" curve, with or without changes, you will need to remove the jumper.

What are the advantages of using the full "B" curve? I assume better combustion, therefore more power and economy?
You are correct. My suggestion to cut back on the advance of the "B" curve is simply to start out conservatively and move up to the full curve, once you feel comfortable with it. There is no reason you can't start at the full "B" curve, many people have done that without issue.

At some point can you go to far with the advance and start getting in to danger?
YES! I would not play with the timing settings (beyond the "A" and "B" curves) unless you have a full EMS w/ CHT and EGTs for all cylinders. We talked about developing a knock sensor for the Lycoming engines but backed off. Cars typically use one knock sensor plugged into the engine block, which works fine for those quiet running engines. Our aircraft engines are very noisy and what we found is that we would require a knock sensor on each cylinder and then some serious computing power (hardware and software) to filter out the noise on each cylinder. Once we had that info, there isn't much we could do with other than display it since we don't control anything. Your rising CHTs are a good indication of pre-ignition. (I'm not talking about poor cylinder cooling here.)

We did work out a way to mount knock sensors on stock cylinders but that is a different story. Ironically, Lycoming's TEO-540-EXP twin-turbo engine with the integrated iE2 electronic engine management system also uses knock sensors mounted on custom cylinders.
 
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Maniford Presssure

What role does manifold pressure have on the advance curve? What is the interaction between manifold pressure, rpm, and advance curve, or does anyone have a pmag look up table which shows this interaction?
 
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What role does manifold pressure have on the advance curve? What is the interaction between manifold pressure, rpm, and advance curve, or does anyone have a pmag look up table which shows this interaction?

Mike,

The timing crave is proprietary to Emag, and I can only guess what the relationship between RPM and MAP are.

We just added the advance numbers to the EICommander's Timing Divergence Alarm screen:

TDA%20with%20Advance.jpg

The green indication on the left side of the display indicates the timing difference between the two ignitions, 2.0 degrees or less in this example. The chevrons indicate the current advance for the right (green) and left (red) ignitions. The vertical bars on the right report the health of the coil packs, wiring harness and plugs. Too low a number and you have a short or fouled plug, too high a number and you have an open lead or broken wire.

Flying with the above screen, our Beta tester found the following during a recent test flight:
Engine: 180 hp IO-360, CS Prop, and dual P-mags

Take off
RPM: 2700
MAP: Full throttle
Advance: ~ 27 deg

High Speed Cruise
RPM: 25
MAP: 25
Advance: ~ 29 deg

Low Speed Cruise
RPM: 2400
MAP: Unknown but lower than above
Advance: ~ 33 deg

This indicates that when the engine is working its hardest, the EPIs limit max advance but when it slows down and is lightly loaded, it can call up more advance. That is working as it should.

For those of you flying with the EICommander, this software update will be made available shortly.
 
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RE:Hot Start ??

I have a Titan ECI IOX-360 in my RV7A with ram air induction. I am also running with dual 113 PMags. I am using the jumpers / with the MAP from the mags not coneccted to the MAP sensor. The engine has 100hrs on the hobbs and at ROP the cylinders are running with 1 the coolest, 4 next with 2 and 3 the hottest (365/385/395/400+ @ 8500 msl and 70 OAT @ 10.9 GPH LOP they nearly always break with 4 first then 3 then 2 then 1 (335/355/358/360 @ 8500 msl and 70 OAT) @ 6.8 GPH.

Cold start are flawless. Engine runs smooth all the way through taxi/run up / climb / cruise / landing / taxi to hangar / and shut down.....

Now for the hot start that is another question. (this is the only way I have found that will start the engine and I have nearly ????( there maybe one that I don't know about) tried them all).

1. Mixture full Rich
2. Master on
3. both PMags on
4 "clear prop"
5. turn on high pressure fuel pump
6. hit start

prop will turn maybe 10 times and the engine will begin to show life.

7. Let go the start bottom.
8. The engine will run rough ...but if I shut the fuel pump off to soon the engine will stop.
9. At a point in time about 5 seconds the fuel pump will be turned off.
10. Engine will still run but a bit rough and on a few occassions has back fired.
11. By the time run up is completed / and ready to launch the engine will finally run smooth but not as smooth as from the cold start.

NOW THE QUESTION..... Could this hot start problem be a PMag timing-set up problem? Or................

Frank @ 1L8 ...RV7A... Flying and Tracken MT-RTG
 
I have a Titan ECI IOX-360 in my RV7A with ram air induction. I am also running with dual 113 PMags. I am using the jumpers / with the MAP from the mags not coneccted to the MAP sensor. ...

Now for the hot start that is another question. (this is the only way I have found that will start the engine and I have nearly ????( there maybe one that I don't know about) tried them all).

...

NOW THE QUESTION..... Could this hot start problem be a PMag timing-set up problem? Or................

Frank @ 1L8 ...RV7A... Flying and Tracken MT-RTG

My first question is, when did you have them last upgrade? If you haven't had them upgraded since Emag fixed the lost timing issue, get them in before your next flight.

By plugging the MAP line to the P-mags you force them to "retard to an operable, but much less efficient range."

The P-mags have a "shower of sparks" starting mode. This works below 200 RPM, IIRC.


I have suggested that people running injected set the RMSD (Run Mode Start Delay) on the left mag but leave the right RMSD set to 0.

The RMSD is the setting that keeps the E/Pmags from firing until X number of revolutions.

The thing to keep in mind is that the RMSD works for the first starting attempt only. Meaning that if your engine doesn't start and you have to use the starter a second time, there is no RMSD for the second attempt. To rest set this feature, you have to power cycle the E/P-mags.

On a cold start, use both mags and the right one will fire on the first revolutions.

On a hot start, use just the left ignition which will allow the engine to turn over a few times before firing the ignition.

Give that a shot and let us know how it works.
 
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RE:Updates !!!

Bill

Thanks for the info.... My updates have all been complete...

Next time I have the cowl off I will give your suggestions a try. Plus I wished I was flush with more beans the EICommander looks like a great instrument to have for diagnositics

Frank @ 1L8 ...RV7A... Flying/Tracken MT-RTG
 
Mike,

The timing crave is proprietary to Emag, and I can only guess what the relationship between RPM and MAP are.

We just added the advance numbers to the Timing Divergence Alarm screen

TDA%20with%20Advance.jpg

The green indication on the left side of the display indicates the timing difference between the two ignitions, 2.0 degrees or less in this example. The chevrons indicate the current advance for the right (green) and left (red) ignitions. The vertical bars on the right report the health of the coil packs, wiring harness and plugs. Too low a number and you have a short or fouled plug, too high a number and you have an open lead or broken wire.

Our Beta tester found the following during a recent test flight:
Engine: 180 hp IO-360, CS Prop, and dual P-mags

Take off
RPM: 2700
MAP: Full throttle
Advance: ~ 27 deg

High Speed Cruise
RPM: 25
MAP: 25
Advance: ~ 29 deg

Low Speed Cruise
RPM: 2400
MAP: Unknown but lower than above
Advance: ~ 33 deg

This indicates that when the engine is working its hardest, the EPIs limit max advance but when it slows down and is lightly loaded, it can call up more advance. That is working as it should.

For those of you flying with the EICommander, this software update will be made available shortly.

I have had EI (Electroair & Subby) with a timing advance meter of some sort. At WOT on take off timing always was around 24 degrees. What is the advantage of running at 27 degrees? I would be concerned about heat at that power setting.
 
I corrected post #14. It is the RMSD that gets reset with a power cycle of the E/P-mags.
 
I have had EI (Electroair & Subby) with a timing advance meter of some sort. At WOT on take off timing always was around 24 degrees. What is the advantage of running at 27 degrees? I would be concerned about heat at that power setting.

David,

Under heavy load, such as at full power takeoff, most EI's limit the advance, 24 degrees in your example, to preclude pre-ignition.

At high altitudes and lower power settings, such as at cruise, most EI's will allow for greater advance settings.

The idea is that there is less fuel & air in the cylinders when operating at lower MAP's and it takes a longer time for the flame to propagate across the entire cylinder, so they can start it burning sooner.

At high power settings (MAP), the fuel/air mixture will burn faster because there is more fuel/air. Thus the EI's delay when to ignite the mixture until closer to TDC (Top Dead Center). If the mixture burns too fast or too far before TDC, the maximum pressure could be well before TDC, which you hear as engine destroying pinging.
 
Ahead of it's time...

Bill/David,

I purchased one of the first Electroair Ignitions from Jeff Rose back in the 90's for my RV4. I did alot of experimentation with my single mag, EI, spark plugs and Mag advance over the 1500 hours I flew my -4. I found that setting my non impulse coupled Bendix mag to 22 BTDC, EI installed standard (TDC) and using REM-37BY plugs for the Mag and Autolite 386 (18MM) plugs for the EI I achieved the best results. Starting was easy, no pre-ignition and always showed 8GPH at 20/2500 at 10,500 feet 165 knots true with 150 horses. EI advance was always around 33. My Rocket has the identical setup as my RV4. With GAMI injectors and the same plugs, Bendix Mag advance I achieve 10.5 GPH LOP at 20/2400 at 10,500 doing 185 knots true. (33 advance) Not bad for SIX cyllinders!

Jeff Rose once told me he set up a Long EZ with two EI's way back in the day. He installed one Hall effect at slightly before TDC and the other slightly post TDC. This gave him a very even burn across the power range.

I always start hot or cold on the EI, then bring the Mag on line when she fires. IO-540 procedure:
Cold: 3 seconds boost with mixture rich, throttle cracked, EI on, CLEAR!
Hot: Mixture lean, no prime, Mag/EI both on, throttle cracked, CLEAR! AS soon as it pops, Mixture rich, boost on.

Electroair still makes a fine system, I like the flexibility and efficiency.

My Dos Centavos...

Smokey
HR2
RVX
 
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EI advance curve discovery

What role does manifold pressure have on the advance curve? What is the interaction between manifold pressure, rpm, and advance curve, or does anyone have a pmag look up table which shows this interaction?

The only reason we don't have a timing map is no one has taken the time to make one and share it. I only see three or four variables here, and each are controllable by simple tools.

Base timing
RPM
Manifold pressure
Ambient pressure
Could be done on a bench or in the airplane.

The EI commander can show timing advance so this would be easy to do and would be a benefit to the community here.

Why isn't EI sharing data?
In past conversations with Brad, he made it real clear they want to be a hardware seller, not the engine optimizers (the timing curve design/engineer). He stated he would like to see the engine sellers come up with their own timing maps via testing. So... basically they they aren't going to share what is going on inside the unit. My read on this, Brad knows builders want a bolt on solution and that a ignition system with no ignition map wouldn't sell very well. At the same time, they don't feel like they are the "timing experts" and their are other entities better suited to make those decisions. :) So, we are left to our own devices, but not that hard really, probably hardest thing to do is get the materials and protocol together, the testing might only take a few minutes.
 
Pelican's perch #43

David,

Under heavy load, such as at full power takeoff, most EI's limit the advance, 24 degrees in your example, to preclude pre-ignition.

At high altitudes and lower power settings, such as at cruise, most EI's will allow for greater advance settings.

The idea is that there is less fuel & air in the cylinders when operating at lower MAP's and it takes a longer time for the flame to propagate across the entire cylinder, so they can start it burning sooner.

At high power settings (MAP), the fuel/air mixture will burn faster because there is more fuel/air. Thus the EI's delay when to ignite the mixture until closer to TDC (Top Dead Center). If the mixture burns too fast or too far before TDC, the maximum pressure could be well before TDC, which you hear as engine destroying pinging.

I suspect you mean to preclude detonation? :D Easy to get the two confused, but if ignition wires are routed correctly and the timing chip not scrabbled, then its really detonation we are worried about, not so much pre-ignition.

IMHO, the best description of what goes on in our Lycoming cylinders is by Deakin, "Detonation Myths" http://www.avweb.com/news/pelican/182132-1.html Probably a good read in terms of understanding what is at stake with our choice of timing advance.

Deakin also points out that you won't hear pinging in an aviation big bore, as the frequencies produced are linked to the diameter of the chamber, thus the noises are lower frequency, and close to the usual noises coming from the engine.

I appreciate his detailed explanation of the different levels of detonation coupled with the timing and pressure maps of the cylinder. Even if you've got heavy detonation, don't expect to hear it, you might see really high CHT's if you are paying attention and have a probe in the offending cylinder. Otherwise, when you have the severe detonation long enough, the burnt valve or hole in the cylinder may be the first clue.
 
Hmmmm.

The EI commander can show timing advance so this would be easy to do and would be a benefit to the community here.

I'm hearing nothing but silence on coming up with a timing map :mad: . Have I stepped on toes here or???
 
Looks like this thread died out some time back.
Bill,
I overhauled a 150 hp O-320 to, hopefully, around 180 HP or so with more compression and Ly-Con cylinders and indexed cam. What should I do with my P-mag? I cut the jumper to run smoother on 7:1 compression. Figure I need to reconnect at 9.5:1. Any other suggestions? Was hoping to upgrade to two EI but didn't get there.....

Updated post for accuracy!
 
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My suggestion is at 10:1 CR you do not want advance of any great amount. My thoughts on this are best not made in this post, so you could read between the lines.

I would strongly urge you to research the mag timing of high compression engines and make an educated decision.
 
This is a tough question because of your high compression pistons. I hope someone else jumps in with experiance and comments.

With the jumper the timing starts at about 26? BTC. Without the jumper it starts around 31? BTC.

It seems to me that with your pistons, you might want to try moving your timing in the other direction.
 
Resurrecting a really old thread........

Bill,

Now that the PMag 200s are shipping, does the EIC32 support them? If not, is there a plan to?

Bob
 
Bob,

Recommend you look at the six cylinder pMag install manual. For this pMag you set the maximum advance during install - in other words it is not the binary ?jumper in or jumper out? option.

Carl
 
I am posting to revive this old thread.

The graph in OP #1 post shows a very aggressive curve. Of course MAP is not shown which is POWER. The graph would be better if showing PERCENT POWER to advance not just RPM.

The following post #12 gives some information but it has some big holes and not specific MAP for two of the three data points, Takeoff, High Speed Cruise, Low Cruise.

Take off, full power is 27 Deg. Gives RPM 2700 but does not give MAP. Assume 100% power, about 30 inches. Not radical, but over 25 Deg. I assume setting base line timing back 2 degree can fix that.

HIGH Cruise does give RPM/MAP. 25/25, which is about 78% to 79%, with advance of 29 Degree.

Low Cruise it states 2400 RPM and less than 25" MAP.... Assume 24/24.... about 65% The advance is 33 degrees. That is the PMag max advance correct?

I never want over 25 degrees advance between 75% to 100% power. Nax advance of 33 degrees at or below 60%.

So to ask the question again, HAS anyone plotted out better data with RPM, MAP, OAT, Altitude?

I know there are problems reported with the EMAG but many of those are known and managed, BUT HAS ANYONE EVER HAD ENGINE DAMAGE DUE TO DETONATION.
 
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...

So to ask the question again, HAS anyone plotted out better data with RPM, MAP, OAT, Altitude?

...[/B]

I don't know if the EICommander eic32 provides the current advance value that could be used by an EFIS to plot this data along with the other parameters you mention. I believe that the Engine Bridge has this capability. I have the original EIC and I do look at it from time to time, and never see more than 25 when under high power. I would like to have this plotted along with my other data in Savvy but have so far been too lazy to decode the serial data coming from the pmags to capture it and send it to my EFIS.
 
I don't know if the EICommander eic32 provides the current advance value that could be used by an EFIS to plot this data along with the other parameters you mention. I believe that the Engine Bridge has this capability. I have the original EIC and I do look at it from time to time, and never see more than 25 when under high power. I would like to have this plotted along with my other data in Savvy but have so far been too lazy to decode the serial data coming from the pmags to capture it and send it to my EFIS.
Thanks for the reply. I found some more threads on subject, and also talked to Brad, Principle of EMag. Satisfied PMags I bought will do the job safely and fill my need for my engine to go bang.

The EI Commander is a nice accessory, but not necessary or needed to use the PMags. The EI Commander (separate company) gives timing advance indication of the PMag in cockpit. I believe it can shift the timing curves. Other EI systems have this capability and can make infinite changes to timing advance curve map or schedule. I personally don't need to fiddle with my ignition and monitor it's advance in cockpit. Nothing wrong with that just not necessary for my mission.

I looked at all the other Electronic Ignitions (for decades back to Jeff Rose), SDS CPI-1 and CPI-2, Lightspeed, Electroair, FlyEFI and SureFly. There are many common characteristics. They all have high energy spark, can use automotive plugs with larger gaps, and advance timing at lower power. All this is better efficiency; the plus going for Pmag's is easy installation, easy setup, and has self sustaining internal power, if you lose ships power.

They have been out for over +15 years, 10,000's of hours, and early bugs have been identified, sorted, eliminated or mitigated for sometime. At Oshkosh 2021 I asked big engine builder what EI he recommended. He said PMag.
 
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