Time for a magneto upgrade

by | 2024-06-15

Improving the old reliable magneto with an electronic ignition system

General aviation aircraft engines have been around for ages. The technology has evolved into super reliable propulsion source.

One does not have to dwell too long on the punishing environmental and certainly difficult operating conditions. Yet well maintained and operated there is an excellent chance that a classic engine will make it to its planned overhaul time of generally 2000 hours.

So why change a winning condition? Considering the cost of newer, more modern types of engines many prefer to stick with the respectable Continentals or Lycomings of this world.


Those reputable engines count on one accessory of incredible dependability: the venerable magneto. Here we have a mechanical success story that sits on top of so many others. For the story, the magneto (“mag” for the intimate) generates independently electricity to the spark plugs at a set point in the compression cycle. Usually one sets this point at 25 degrees before top dead centre (BTDC).

I will not develop on this point 4 cycle engine theory. But a lot of smart people have determined under average conditions that an empirical 25 degrees BTDC is good compromise for adequate combustion (power).

Mechanical cut out view magneto
The magneto precise clockwork

“Homebuilders” – experimental aircrafts lead the way

Over a few decades now the experimental aircraft world has been flying around with optimized engine components in order to improve efficiency. Thanks to the fact that onerous certification is not required in this airworthiness category.

One of those components is the electronic ignition system – electronic mag – if you will.  Our old standard engines revamped with new technology magnetos have been getting  successful results so much so that a few manufacturers have managed to certify their “emags”.

A simple concept that evidently had to work its way against well established paradigms   arrived in the certified world about 10 years ago. Hey, I am writing about this, granted well past the “innovation” point. I caught up on the issue just recently… In many respect, I was part of this paradigm problem, not anymore!

Theory behind the concept: cost saving!

First, a legacy magneto is composed of all sorts of smaller parts within, much like a clockwork, so it appears to a pilot like me! Mags need to be overhauled because of these. Every 500 hours, they must be pulled from the engine, packed and sent to the repair shop. They then get resent – like new – to be re-installed by your mechanic.

This no longer required with an electronic ignition system. You guessed it, from the start, the emags require to be pulled every 2000 hours. Do the math and see how quickly one can amortize the purchase price and installation cost.

Another advantage is the improved combustion the emags offer. First the timing is variable and adjusted automatically according to engine RPM and density altitude. The emag has a tube that connects to the intake manifold. In effect, during the compression stroke rather than sparking at a constant 25 degrees BTDC, the spark can be easily be triggered 35 BTDC thus providing more time for the flame to propagate within the cylinder.

New and old: the new kid in town

Second and not least, is the spark size generated. It is much larger and hotter, further assisting the flame propagation. A standard spark plug on a Lycoming will be gapped between 0,016 to 0,021 inch while under legacy magneto control. The emag spark plug gapping requires a much wider 0,022 to 0,035. if you ever paid attention during an annual, the mechanics set 0,028, this is really wide!

So improved combustion equals improved performance or better fuel economy for one same power setting used in the past.

Two types of installation exist: 1 magneto replacement or the two magnetos replacement (full emag setup).

On the single mag replacement, the electronic magneto will fire all the time prior the legacy mag. The legacy mag spark will be somewhat redundant when it fires some 10 degrees later but it remains in place for understandable redundancy and safety. By the way, the emag gets its power source from the aircraft’s battery connected on a “hot battery bus” or directly ahead from the battery prior the master switch relay.

The double emag setup is connected to the battery in the same fashion but also includes a backup battery circuit.

For the record, I have been taking engine performance data on essentially all cruise phase since I acquired the PA-30. It appears tedious for many but really it is not a big deal to enter into a home made database. The intent is to monitor the aircraft a little closer and provide hard comparable evidence when occasional improvements are installed. 

Different manufacturers

I had been shopping around prior to my visit at Lakeland’s Sun n Fun 2024. I was quite prepared with a decent background to have constructive discussions with the 2 main certified manufacturers. The people at Electroair and Surefly were quite candid about their excellent products.

Over at Electroair their marketing puts a good emphasis on pilot testimonials on improved performance. Much less so over at Surefly. Either way no guarantees are made regarding fuel consumption reduction. Fuel consumption and performance improvements can be so subjective when an engine is not run from a testbed. Nonetheless the physics remain the same both ways. Fuel consumption will be less especially at the higher altitudes for normally aspirated engines.

Finally, I went for the Surefly installation which was simpler to install and 2 pounds lighter than the Bendix mag being replaced. Keep in mind that if your aircraft battery is installed ahead of the firewall, the connection to the magneto uses a short wire, great. In this PA-30, the battery is installed way back behind the aft baggage compartment. The installation required the tedious operation of removing seats, side panels and floor in order to route the wiring from the engines to the battery. A larger wire gauge was used because of this extra length. Since the whole cabin was exposed, the certified mechanic at Aviation tion R.Goulet took a good expert look for any subtle snags developing or hints of corrosion especially in the spar area. With the recent AD’s issued for Cessnas 177 and 210 or the new one for Pipers PA-28’s and 44’s one cannot be too complacent.

And now for the inflight result. The envelop please…

No matter how one slices it, fuel consumption came down measurably for the same true airspeed at higher cruise altitudes (8000 to 9000 feet). Each engine consumes less and by 0,75 to 1 gallon per hour. This is established by on the onboard fuel flow indication and by the global fuel boarded vs air time. Power setting set at around 65% and peak EGT.

Another advantage not stated by various publications is the ease of start. The PA-30 is traditionally equipped with two impulse coupled magnetos per engine. Starts are never a problem under normal condition. However, I can’t wait for winter, OK not that much, to test this out. But most aircraft have only one mag with impulse coupling. With an emag installed, starts are reported quite similar to an automobile start.

The total installation cost in my books will be absorbed in just about 3 years of operation at about 100 hours/year. Aviation is a serious business. The installation of the new mags was quite interesting to say the least. Regardless what a hoot!

You have a question? Do not hesitate to write marc@aviationcommonsense.net

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