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Dual Pmag Spark Plug wiring

Bob Martin

Well Known Member
I am planning a dual Pmag install on a RV-6 o-360 carb'd set up. Replacing two Slicks.
Wondering if others have used one mag for top plugs and the other for bottom plugs, or set them like like Lycoming does with Slicks. Or if there is an advantage either way?

I understand the bottom plugs are more prone to fouling from worn cylinders or running rich(catching lead balls), so having a mixture of some bottom and some top could be benificial, but not sure that happens with electronic ignition's hotter spark.
Also when using LightSpeed with their coils mounted on top of the engine, it makes sense to run them to all top plugs, but the Pmags originate the wires from the same place as the Slicks so the option is on the table.
Thoughts?
 
I've installed dual Pmags on two airplanes using "all top and all bottom" (contrary to the std magneto practice) without issue. The SDS CPI on the Rocket is the same way. No fouling, no noticable difference doing "mag checks". I will likely be removing the Pmags on the -8 in favor of the CPI and will again do the same.
 
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It's worthwhile to note that "top and bottom split" mag wiring isn't an industry standard. Many small Continental's are wired with one mag firing the top and the other mag firing the bottom plugs. The explanation often given for Lycoming's split wiring is to reduce the differences in mag drop between the two mags and to provide more even plug wear. I don't believe these concerns are a factor with electronic ignition.

I'm running a single P-Mag wired to bottom plugs and for our first engine start this week it was only the P-Mag that was firing. It had no trouble starting the engine, despite the accumulated "gunk" from 12 years of being pickled.
 
When helping sort through P-mag installation issues, I typically recommend the split wiring to eliminate a significant difference in mag drop when testing, as mentioned above.

That said, with the larger gap we run using auto plugs, they don't tend to get oil fouled, but it can happen. When it does happen, then the pilot only has one way to verify and that is to remove the plugs and inspect them. Not fun at any time and more so when on a trip.

Check your PM's.
 
I just finished a dual P mag installation on an RV8. I found It easier to run and secure the wires from the right mag to the left top and left mag to the right top. Then the right mag to the right bottom and left mag to the left bottom. Also get extra crimp ends for the spark plug so you can cut the wires to the correct length.
 
When helping sort through P-mag installation issues, I typically recommend the split wiring to eliminate a significant difference in mag drop when testing, as mentioned above.

I'm not seeing any difference in drop with EI's wired all #1 on top and all #2 on bottom.
 
I'm not seeing any difference in drop with EI's wired all #1 on top and all #2 on bottom.

On a new installation, there probably isn't a difference but after 50+ hours there is usually a difference. Not a large one but still a difference, when running P-mags.

When helping diagnose P-mag issues, I recommend splitting them, among other things.
 
Top and Bottom

120 hours on the plugs. One Pmag all top and the other all bottom. No difference in RPM drop on mag test... FWIW
 
On a new installation, there probably isn't a difference but after 50+ hours there is usually a difference. Not a large one but still a difference, when running P-mags.

When helping diagnose P-mag issues, I recommend splitting them, among other things.

That has not been my experience. The -8 has hundreds of hours on the dual Pmags and there is exactly zero, none, nada, mag drop. The only way I can tell the switch is doing anything is the EGT rise.
 
That has not been my experience. The -8 has hundreds of hours on the dual Pmags and there is exactly zero, none, nada, mag drop. The only way I can tell the switch is doing anything is the EGT rise.

I'm not surprised Mike. Some people have an issue and some don't.

I'm not sure why or what causes it; however, when someone calls with an issue and they split them, the RPM difference goes away.

Either way, it isn't difficult to split them during installation, which avoids possible issues down the road.

Each installation is unique as the person installing them. So the the results vary.
 
Hi all

Just installed (yesterday) double Emag/Pmag on our RV6A with a Lycoming O320, replacing original ones.
The start is swift and crisp for the first time in years. Just as announced.
First flight was made today and the engine sounded great!
We'll now have to install ventilation for the Pmags, as we have very hot summers in Portugal, any draft/photos/recommendation?

Carlos Costa
 
I got dual P-mags on my 9 w/O320 carbed, i split the wires. Used to start with half of crank now it takes white of bit to start. Not sure why yet. I will be pulling the plugs out to check. Unless someone can tell me about any other issue. Also on the mag check I get a noticeable drop between running both to each individual. Why?
 
Thanks Mickey Coggins

That was my idea! What diameter are those vents?
They seam a bit slim. Is that enough?
Are monotoring the Pmags temperature?

Regards

Carlos
 
This might be an easier way.

I drilled a hole in my baffle to match the "valley" in the blast tube and then used RTV to secure it in place.

Using two Adel clamps, one on the engine mount and one on the blast tube, I aimed the blast tube at the neck of the P-mag.

Here is the picture I have:


(Click to enlarge)

One other thing, make sure you have some type of restrictor in your manifold pressure line to smooth out the pulses in the MAP line.
 
I have dual P-mags installed with each one firing both top plugs on one side and the bottom on the other. The bottom plugs will always have more lead build up than the top ones.

You can see the lead blob built up on a bottom plug here. (and yes, I lean aggressively on the ground and fly Lean-of-Peak)
IMG_4971-M.jpg


The plugs get tossed every 100-140 hours. The automotive ones only cost about $24 to get eight new ones.
 
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