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Old 01-18-2019, 06:57 PM
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N941WR N941WR is offline
Join Date: Jan 2005
Location: SC
Posts: 12,884
Default P-mag Timing Explained

Axel, thank you for the picture!
Originally Posted by AX-O View Post

I also set the timing of the PMAGS and configured the "B curve" as shown below. Set the Max engine RPM to 2816, dropped the Max Advance to 33.6 deg and subtracted 1.4 deg on the curve shift. Will play around with this once I get more familiar with it. For now the instrument will remain off along with ADSB since I have to get back in the cockpit. Trying to minimize the info coming in that is not required.

This is a great picture of our new EICommander EIC32 that Axel posted on his Fast Back thread.

I am writing the following to help explain how the timing should be set on engines running P-mags.

This seem to be especially important for those running angle valve engines (IO-360, 390, & 400's).

The following assumes the P-mag timing marks are set at the TDC. All examples for standard 8.5:1 compression parallel valve engines. Below will be some numbers for angle valve engines.

Everything I describe below can be configured with either an EICoimmander, with the EICAD program available from Emag Ignitions, or by clocking the ignitions as described in the Emag Electronic Ignition Installation & Operating Guide available here.

Displayed in this picture it the timing configuration page from the new EICommander EIC32. This is a custom "C" configuration that Axel has made and sent to his P-mags.

First, the standard P-mag "A" jumper in configuration has a the following settings:
RPM Max (Rev limiter): 3328 RPM's
Advance Shift: 0 - This equates to 26.6 degrees before TDC.
Max Advance: 35.0 degrees before TDC.

Max RPM;
Axel reduced the point where the P-mags will stop firing to 2816 RPM's. This is good because should he have a prop governor failure, the P-mags will limit the overspeed to this number and help him avoid an engine overhaul.

Advance Shift:
By setting the Advance Shift to a -1.4 degrees, the high power timing setting will be 25.2 degrees BTC.

Max Advance:
The Max Advance is exactly what is sounds like. As the manifold pressure drops off with altitude and throttle setting, this is limits how far the P-mags will advance.

Run Mode Start Delay allows the engine to delay firing the sparkplugs for a set number of revolutions. Zero is the desired setting. If you change this to two (2), the engine will make two complete revolutions prior to firing the sparkplugs. If this is set to any value other than zero (0), the engine will pump raw fuel out the exhaust ports, which will light off with a bang once the ignition comes on line. Thus we highly recommend it be left at zero (0).

The allows you to turn on and off the external LED. Leaving it set to "SENS" allows you to see the LED turn red, yellow, and green as required to set the timing. In the newer EIC32, we do not allow this to be changed.

A few comments about P-mag configurations:
1. We have not heard of any Lycomings where the P-mags should be run on the "B curve" (no jumper). The "B Curve" starts firing the ignitions at 30.8 degrees BTC and advances out to 39.2 degrees.

2. The configuration Axel has selected appears to work very well for Parallel valve engines. We have enough experience with it to say that in a typical installation, this will reduce the CHT's 10 to 20 degrees F and increase speed a few knots over the standard "A" - jumper in configuration.

3. If you run an angle valve engine (IO-360, 390, 400, etc.) that requires a 20 degree timing, neither the "A" nor "B" curve should be used when the P-mag's timing mark is set to TDC. Using either of these configurations could damage your engine.

There are three ways to set the timing for these engines. One is to "clock" the ignitions, similar to how the timing is set with a standard magneto. Contact Emag Ignitions for details.

The other two options are to create a custom configuration with either an EICommander or the free EICAD program from Emag Ignitions.

Again, this assumes you have set your timing mark to Top Dead Center.

Advance Shift:
-7.0 will cause the P-mag to fire at 19.6 degrees BTC during high power operations such as takeoffs.

Max Advance:
29.4 will limit the maximum, lower power advance to this value.

These engines should never be set at TDC and then run with either the jumper in or jumper out. Either of these configurations may damage your engine when the TDC mark is set to Top Dead Center.

CHT cooling on angle valve engines seems to be much better than parallel valve engines. Do not take acceptable CHT's as an indication that all is OK with your engine while running excessive advance in your angle valve engine.

If you have a high compression engine, consult your engine builder for the proper timing advance.

As always, feel free to contact me off line, if you have questions. I am more than happy to help protect you and your engine. I don't care if you are an EICommander customer or not, I am happy to help.

Either Angle or Parallel Valve engines:
Finally, if you have a new engine, or a newly overhauled engine, I recommend you set the Max Advance number to equal your high power timing number for the first 10 hours +/-. This way, if you experience high CHT's for the first ten hours or so, you know the issue isn't a result of your timing advance and is probably the result of a baffling leak. After your CHT's drop, then change the Max Advance number as appropriate for your engine.

Clocking your P-mags:
Emag Ignition's preferred method of setting the timing is to not use the EICAD program but rather "clock" the timing mark. This achieves the same things as adjusting the internal timing values with either the EICAD program or the EICommander.

Originally Posted by Emag Igntion's 114 manual, page 13
CLOCKING: Set timing with the engine positioned slightly after TDC (1-6 degrees). Greater offsets will produce greater retard (less aggressive advance).
This does not require you to purchase any hardware (USB to serial connectors, EICommanader, etc.) or install the EICAD program on your computer. It accomplishes the same thing by moving the initial firing point and should be accomplished with the jump installed between P-mag pins 2 and 3.

Remember, the goal is to fire the spark plugs at the point recommended by your engine builder, any way this is accomplished is beneficial to you and your engine.

DB9 Connectors:
The following image is what I recommend to builders who install P-mags and plan on adjusting them with either the EICAD program or adding an EICommander later on (If you are going to start with an EICommander, wire them as recommended in the EIC manual. As stated above, it is not required, if you plan on "clocking" the ignitions to achieve optimal timing. This will allow you to connect to the P-mags with a PC from inside the cockpit and should you later decide to install an EICommander, you can make a simple wiring harness to join both P-mags to the EIC.
"No jumper" is depicted because the drawing assumes you are going to customize the P-mag configuration. If you elect to run the standard "A Curve", place the jumper at the DB9 plug.

Hand Proping:
Do not hand prop your plane, unless you have been trained in the fine art of hand propping.
If you expect to need to hand prop your aircraft, contact me off list (include your email address), and I will send you a wiring diagram on how to wire in a 9 volt battery to one P-mag.
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC

Last edited by N941WR : 01-24-2019 at 07:43 PM. Reason: Added comment about "Clocking your P-mags"
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