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-   -   E/Pmag timing advance explained (https://vansairforce.net/community/showthread.php?t=62158)

N941WR 09-04-2010 07:41 PM

E/Pmag timing advance explained
 
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 [url=www.eicommander.com]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.

carguy614 09-05-2010 05:40 AM

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

N941WR 09-05-2010 06:33 PM

Quote:

Originally Posted by carguy614 (Post 464668)
...
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.

apkp777 09-05-2010 06:50 PM

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.

N941WR 09-05-2010 08:22 PM

Quote:

Originally Posted by apkp777 (Post 464826)
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.

IowaRV9Dreamer 09-05-2010 09:15 PM

what do pmag jumpers do?
 
Quote:

Originally Posted by apkp777 (Post 464826)
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.

N941WR 09-05-2010 09:48 PM

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.)

N941WR 09-05-2010 10:01 PM

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.)

apkp777 09-06-2010 05:44 AM

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?

N941WR 09-06-2010 07:36 AM

Quote:

Originally Posted by apkp777 (Post 464893)
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.

Quote:

Originally Posted by apkp777 (Post 464893)
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.

Quote:

Originally Posted by apkp777 (Post 464893)
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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