Out with the Old, In with the New

Upgrading from Slick magnetos to P-MAGS.


Seven or eight years ago, when I was buying equipment for my RV-8 project, I was intrigued by the (then) new E-MAG electronic ignition. Intended as a drop-in replacement for regular magnetos, I sure liked the clean design that did not require a separate brain box, crankshaft sensor or extensive wiring. It seemed to be a great design concept—but to be honest, I was a little nervous about trying something so new that absolutely must work to keep the airplane in the air.

The complete P-MAG kit—mags, plug harness, plug adapters, install kits, and a bag of popcorn.

I decided to go with tried-and-true Slick mags and keep an eye on the E-MAGs. I watched as numerous people went with one, then two of the units, as well as the even-newer P-MAG—an E-MAG with an internal alternator, so once it’s going, it keeps the engine running independent of ship’s power. This really upped the interest, since it’s pretty much as electrically independent as a traditional mag, except for starting.

After some early teething problems with temperatures and mechanical components, it appeared that folks I have a lot of respect for were piling up hours on their P-MAG installations. Reports of difficulties became few and far between, and reports of improved customer service on the part of E-MAG Ignitions went up. I saw both of these as positive signs, so when it came time to have an engine built for our new RV-3, we pulled the trigger and went with dual P-MAGs to get the maximum benefit of electronic ignition (EI) all the time.

Left mag hole, impulse coupler spacer removed—note the long studs that interfere with the P-MAG.

With 1430 hours on the RV-8’s engine, we suffered our first real Slick mag issue. Although I have had great luck with Slicks on a number of airplanes, the left mag died on a long cross-country. Most likely a coil issue, we were able to borrow a mag from a friendly mechanic to get home, and then I started shopping for a pair of new Slicks—the old ones were the same age, and if one coil went, the other was soon to follow. The price of coils and overhaul parts are such that it really makes about as much sense to buy a new Slick mag as it does to fix one that is malfunctioning, so I was looking at about $1600 for a set.

P-MAGs would cost more, but if I was ever going to make the switch, now was the time. And since I was committed (and happy) on the RV-3, I figured I’d go ahead and bring the Valkyrie’s engine up to the same standard. At the same time, it would allow me to see (and share) first-hand what was involved in making the swap. It turned out to be very straightforward and simple, with the greatest time spent in adding a couple of circuit breakers and determining where I wanted to run the wiring to supply ship’s power to the P-MAGs.

As always, making the installation look pretty takes a little extra time, but overall, this was a weekend project, if you don’t count the days I spent waiting on a couple of special parts and tools for my unique installation.

Here are a few notes and pictures to outline the project—one that even a non-builder should have no trouble following.

Removing the Slicks

Pulling the old ignition was a piece of cake. The only things that are remarkable is that the hold-down studs for the left mag will most likely be too long for the P-MAG, since that mag usually has an impulse coupler, which requires a spacer, which requires longer studs. You’ll remove the spacer to install the P-MAG, and will probably want the shorter studs.

You can use a steel-tube spacer (or stack of washers) to take up the extra length of the stud, but it will severely limit the orientation of the P-MAG—there is probably only one way it will fit. Since one of the neat things about the P-MAG is that it can be mounted in any orientation, and some work way better for access to the electrical connectors than others, it sure is nice to have the flexibility. I decided to take the time now and change the studs to make maintenance down the road a whole lot easier.

The Snap-On stud puller is expensive—but not as expensive as removing a buggered up or broken stud from the accessory case. Beg, borrow, or steal one.

The Snap-On stud puller made long stud removal simple—attempts with double nuts threatened to break the studs instead of removing them.

Removing studs can be easy or hard —in this case, I double-nutted them and got nowhere. Some suggested heat, others Vise-Grips—but doing either with the engine on the mount is difficult. I did a little research and found that Snap-On makes a special stud puller that is the cat’s meow; works slick and easy. It is, unfortunately, a $130 tool—outrageous! But compare it to the cost of removing a buggered up or broken-off stud; you’ll be pulling the engine and accessory case. How much will that cost? I was fortunate a friend owned the tool and that made the decision easy—I simply borrowed it. In 10 minutes, both studs were removed and the replacements installed. I used the same shorter studs that are used on the right side, and everything fit like factory new.

The P-MAGs (like other mags) do not come with drive gears—those are engine parts. You can remove and reuse the one from the right mag, but the impulse-coupled mag has a different gear. E-MAG Ignitions was able to supply me with the correct gear. It was marked used, but looked great and that, to me, was an easy way to go—unless you happen to have one lying around. You’ll probably also find that the ignition wire clamps used to secure the wiring harness to the cylinder heads are too small.

Left mag hole with the studs removed.

The automotive ignition wires used by P-MAG are slightly larger in diameter than the aviation harness wire, so you’ll need some larger Adel clamps as replacements. Aside from that, everything is in the box with the P-MAGs—including a bag of microwave popcorn to keep you occupied while reading the manual. And definitely read the manual; there are several things different about P-MAGs, if you are used to installing conventional mags.

Decisions, Decisions…

Once the old magnetos and wiring were out of the way, installation began. I pulled all eight spark plugs, as I had decided to take E-MAG Ignitions’s recommendation and go with automotive plugs. Although I originally wanted aviation plugs just because I was comfortable with them, E-MAG’s Brad Dement convinced me that not only were the automotive plug wires a much better fit, the ignition was really designed to use auto plugs. I had also heard of the benefit of buying $2 auto plugs from other EI users for years—and yes, it was nice to buy a huge box of plugs for the price of a new single set of aviation plugs. E-MAG Ignitions supplies adapters that screw on the plugs to let them fit your Lycoming cylinders, and it all bolts together very quickly.

In with the New

Installing the P-MAGs themselves took no time—and it was really nice to be able to orient them the way I wanted—with the side for the wiring harness plug facing outboard on the engine. This makes hooking things up and doing maintenance down the road so much easier. I simply reused the mag hold-down blocks and nuts, then I was able to route the plug wires to their locations. Each P-MAG comes with four automotive wires—a long one, a short one, and two medium-length ones. It’s not hard to figure out what goes where, but you will need to enlarge the holes in your baffle grommets for the plug wires that go on top. I ran mine the same as I do on Slicks—each mag fires the top cylinders on one side, and the bottom cylinders on the other. You need to look at the drawing to make sure you run the correct wires to the correct cylinders—then check it again several times. With a Slick mag, the distributor cap and labels on the plug ends make it almost idiot proof. The P-MAG expects us all to be better idiots, so check it before you take the time to cable-tie everything in place.

Right mag is oriented so the electrical plug is easily accessible.

Attaching the power and control wires is pretty simple. If you decide to pick off the tach signal, you’ll have four wires to a P-MAG—power, ground, the ignition switch P-lead and a tach wire. There are two other terminals that can be used to jumper the P-MAG for different advance curves, or that can interface to a computer for monitoring and/or control. While some have complained about the type of connector used on the P-MAG, I found that they were fairly simple to use, and look robust if you follow instructions and use the supplied Adel clamp to restrain the wire bundle properly. Since my existing P-leads were shielded wires, where I used the center conductor as the P-lead and the braid as the ground back to the switch and then back to the mag, I had to add an actual ground wire as well. I simply cut the ring terminals off my existing installation, put the P-lead into plug slot #4, the shield into #1 (along with a wire which I ran to engine ground), and the tach signal wire to #6. The new 12-volt power went into #5, and it was time to tie off the bundles.

I supplied power to the two mags through separate 3-amp circuit breakers that I added to the cockpit, and powered from my essential bus. Since the P-MAGs will generate their own power once the engine is running more than 800 rpm, I was satisfied with a single power feed to each, considering that I have two different batteries and two alternators as a way to feed the essential bus. And if the airplane is really dead when I go to start, I probably need to fix that before I go flying anyway. There are very few emergencies that will make you take off on short notice. Being chased by blow-dart wielding Hutu tribesmen is probably one, but highly unlikely, so I consider this an acceptable risk. Adding the circuit breakers and an additional firewall pass-through probably took the most time since I had to pull my panel to do a nice job of running the wires and keeping things neat. This is a good reason to install a few extra firewall-penetration wires when you build the airplane—just in case you want to add something up there later.

After using a T-connector to tap into the manifold pressure hose, I used a Y-connector to split it to the two P-MAGs.

Now for the tach signal line: You’ll have to look up the recommended connections for your particular tach (or EFIS) to see what it is expecting. In my case, I am using a Grand Rapids Technologies EIS 4000 to collect the tach signal and feed it to my EFIS. To hook it up to the old Slicks, it needed an inline resistor to work properly. Fortunately, I had planned ahead for a day like this, and put the resistor in with spade connectors; it was a simple matter of pulling that out and substituting a simple wire with the appropriate lugs in its place. This took almost no time, but since I had an older EIS, I also had to go into the box, using an excellent instruction sheet supplied by GRT, and clip two components—a resistor and a capacitor—off a circuit board. This took about 10 minutes.

One other quick task was the addition of some cooling blast tubes. I have never used them for mags, but the P-MAG instructions specify blast tubes to cool the round-neck portion of the units. Since they had early problems with temperatures, I think it is very wise to follow their instructions. I simply drilled two holes in the back of the engine baffles, inserted ¾-inch corrugated hose, and pointed them right at the specified area, using safety wire to hold them in place. (Another 20-minute job.)

The (older) EIS needs to have a capacitor and resistor removed from the middle board to make the Tach work right. This took about 10 minutes.

The last thing I needed to do to hook things up was to add a manifold-pressure line to the two P-MAGs. The easiest way to do this is to route the two lines from the P-MAGs to a static-line quick-disconnect Y-fitting. From there, a single line can be routed to a transducer manifold, or to a T-fitting in your manifold pressure sense line. On our RV-3, I used the manifold. Because of the way I had routed the lines on my RV-8, it was easier to add a T in the line going to the manifold pressure sensor, and secure the T to the engine mount. I like the manifold method better, but didn’t want to run all that extra hose. (You could also take a fresh tap off an unused primer port.) I really like having the quick-disconnect in the sense line because you set the timing with a blow into the hose—and you can pop it off quickly to accomplish this.

The GRT EIS needed a resistor in the tach signal line when used with Slick mags. It was installed with spade lugs in the bundle, so it was easy to remove and replace with a jumper (top), since the EIS wants straight voltage from the P-MAG.

Final adjustments

Speaking of timing, this was the easiest part. Set the prop at Top Dead Center—not 25° before TDC—on any cylinder

and line up the TDC mark on the starter alignment hole or the crankcase seam, whichever you have easy access to. Once there, power up the P-MAGs with the ignition switch off. See the red lights? Blow in the tube until the lights blink, then blow again to confirm and the lights turn green. Blow hard—it takes a little bit of pressure. Reconnect the line, and you’re done. An inspection mirror helps to see the LEDs; one will be easy, one will be tougher to get to. Once this is done, roll the airplane out front and get ready for that first engine start. Make sure your battery is charged up, because you’ve probably been fooling around with it doing all this wiring stuff. If that’s taken care of, set the ignition switch to both and hit the starter. Be ready—it is going to light off much quicker than you’re used to!

I have been really impressed with the quick-and-easy starting on our RV-3, but I had nothing to compare it to; it came with P-MAGs, so it has always started quickly. With the -8, I could get a direct comparison to the old Slicks, and it was like night and day. First off, I have always considered this to be a very nice-starting engine. Now I was surprised at just how quick it lit off—like the proverbial one or two blades. Second, I have always had pilot/passengers remark on how smooth the engine runs—with mags. I was shocked at how smooth it now started and idled with P-MAGs, right out of the box. The ignition is obviously hotter and more powerful, and doesn’t misfire a single cylinder. It is truly remarkable. After a little running on the ground, I cowled it back up and took it for a quick flight around the pattern. Leaning was incredible! Even with a carburetor, you can lean it way, way down into the LOP region without misfiring—and I mean down to where the power is dropping off dramatically (but smoothly). It is going to be possible to run quite a bit leaner than before, and I was always able to run 50° LOP without a problem. True, the leaner you get, the less power (and lower speed) you’ll have, but pick up a nice tailwind, dial it way back and enjoy incredible range. That is what we experienced during Phase 1 testing on the fuel-injected -3, and I expect that the -8 will be similar. It is simply amazing how well the P-MAGs work.

Summing Up

Easy installation, reasonable cost when compared to a full-up Slick system, and few reported problems in the latest installations—I’m sold. I fly lots of cross-countries, and cover lots of ground where I’d rather not land. But I am comfortable now that these have reached a level of maturity that I can trust. True, if I find myself with a dead P-MAG, I probably won’t find one on the field to get me home like I might with an old Slick, but FedEx can reach us just about anywhere these days, and I won’t be stuck for very long. Everything is a compromise, and you might find yourself stuck with a dead mag and no replacement at some out-of-the-way refueling stop as well. But the past few years of demonstrated reliability, plus the smooth starts and potential for efficiency finally tipped the scales for us. We still have one Slick-equipped airplane, and when it needs ignition work, we’ll see what makes the most sense. But the P-MAGs seem to be an easy and sensible direct replacement if you are looking at buying two new mags anyway. And the installation? Piece of cake!

Previous articleLetters
Next articleKeith Hedrick's Rans S7S
Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra and an electric Xenos motorglider they completed. Currently, they are building an F1 Rocket. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, FAA DAR, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.