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Now for a bit of myth-busting:

Surefly claims that the spark from the remaining magneto is totally wasted. This never quite made sense to me, as the amount of advance in time is only a couple of milliseconds. It felt like the flame front from the SF plug might not have reached the mag plug by the time it sparked. Now that the earlier weirdness is no longer a problem I decided to run a test:

Conditions: 7500 ft. OAT 20 degC, DA 9500 ft. MAP ~22", RPM 2400, airspeed 142 KTAS, EGT 1419 degF

Flying on both systems I switched to left "mag" (SF) only. No change in RPM or MAP. No immediate change in airspeed. Engine continued to run smoothly (if one could assign such a term to a 4-cylinder Lycoming) But EGT's immediately started to climb. Within seconds they were beyond 1440. Turned back to both and EGT's came back down.

I didn't run it long enough this way to check what CHT's or airspeed would do. This was just a quick test not central to the purpose of the flight. But it does tell me that the mag sparks still count, improving the combustion completeness over the SF alone. The rise in EGT's is exactly what I've observed running on just a single mag.

I spoke with SureFly last week. They indicated version 2 of the Surefly SIM4N, the 4-cylinder non-impulse mag needed to replace the DA40's Slick mag, will be available in late August or sometime in September. Version 2 of the SIMs does not require the extra external capacitor to filter voltage spikes that were causing engine "stumbling" issues encountered earlier.

Surefly is currently waiting for FAA approval optionally replace both mags with Surefly SIMs. The advantage being to eliminate the 500 hr inspection requirement for both mags and by enabling spark advance feature on both mags, both plugs will participating in the combustion events evenly. Apparently all the work has been done for this but there is no timeline when FAA approval will arrive. The exact same SIM4N part would be used for both mags.

MarkA wrote: ↑Tue Aug 03, 2021 8:03 pm Surefly is currently waiting for FAA approval optionally replace both mags with Surefly SIMs. The advantage being to eliminate the 500 hr inspection requirement for both mags and by enabling spark advance feature on both mags, both plugs will participating in the combustion events evenly. Apparently all the work has been done for this but there is no timeline when FAA approval will arrive. The exact same SIM4N part would be used for both mags.

I'd be comfortable flying behind a pair of these (the new ones that is) where both are connected via individual leads as the one is now - directly to the battery. But I suspect that there is some backup battery involved. And there's the tach signal adapter to deal with.

My understanding is the need for an independent backup power source for the second SIM was a large part of the discussions with the FAA.

I don't know how they ended up solving this but technically it would not a big deal to add a small, replaceable, independent backup battery for the second SIM since it draws such a small amount of current (600mA).

Received a call today that the new version of Surefly SIM4P model is available and they will be shipping it today. Would appreciate recommendations on whether to go with an experienced installer or just about any good A&P?

mysands wrote: ↑Tue Aug 10, 2021 5:02 pm Received a call today that the new version of Surefly SIM4P model is available and they will be shipping it today. Would appreciate recommendations on whether to go with an experienced installer or just about any good A&P?

This is a very straightforward thing to install and the instructions are quite clear. Any A&P should be able to do it. Just make sure it's someone who will pay attention to those instructions.

My understanding is that you actually need the SIM4N module if you plan to replace one of the Slick mags on a DA40.

Version 2 of the SIM4N is supposed to be available from SureFly in late August or September.

MarkA wrote: ↑Tue Aug 10, 2021 8:54 pm My understanding is that you actually need the SIM4N module if you plan to replace one of the Slick mags on a DA40.

That is correct. Is this for a different Aircraft?

Thank you. This was good information to know. Will wait for SIM4N. Rich, it’s for a DA40 XLS. How should I have known it was SIM4N? The application guide on SureFly indicated SIM4P as an option. I have a lot to learn.

mysands wrote: ↑Wed Aug 11, 2021 10:41 am Thank you. This was good information to know. Will wait for SIM4N. Rich, it’s for a DA40 XLS. How should I have known it was SIM4N? The application guide on SureFly indicated SIM4P as an option. I have a lot to learn.

I was researching yesterday because I thought I'd once seen something that led me to think that the FP model might have an impulse-coupled AND SlickStart. I dug a bit more this morning and see that the Wiring diagram for the FP shows a Slick 4373 for the left mag which does have an impulse coupling but is also connected to a SlickStart, though it is wired differently to this mag than for the "normal" DA40 Slick 4374 mag. So the unconditional statement that no DA40's use an impulse-coupled mag may not be quite accurate.

You can easily check whether a given plane has an impulse-coupled mag by carefully rotating the prop (ignition off) and listen as the engine goes through compression cycles. If you here an unmistakable SNAP! this is the sound of the impulse device releasing to generate a more-healthy spark. If you do hear that snap, you have to check the nameplate on the mags to see which one. In the case of the DA40F it should be the left mag.

The drive gears for the two cases are different, hence the SIM4P has an accommodation for adapting to this condition and the installation requires a small bit of extra work.