50hr report, 3 out of 5 stars.
O-360A1A Surefly right side, 25d BTDC fixed timing, Left side a Bendix with impulse coupling.
Likes- avoid the hassle and cost of the 500hr mag IRAN, install was simple, the SIM allows a smidge more leaning.
Dislikes- the install and ops manuals left out two important points. #1 the vacuum port cap problem, don't plug it off, and #2 Inflight mag checks can abuse your exhaust system. #1 I found out when talking to the factory about another matter, and #2 was discovered when doing high power inflight mag tests. The SIM takes a split second to boot up when the P-lead goes from grounded to open. 1/10 of a second doesn't seem long, but it is long enough to push combustible mix into the exhaust, and then when the SIM does wake up. BOOM! Last July, Bill from Surefly reported there was a fix in the works to make the boot up 2 milliseconds. That would be similar to a magneto.
# 3 dislike, kickbacks, so I'm back to starting on the left mag only (impulse coupling). After changing my routine to both, I had a few kickbacks, probably associated with a weak battery at the time, but the impulse coupling with the 25d lag has never done that. Why? Maybe the effective timing is moved forward with both mags firing or a maybe a more powerful spark from the SIM. The starting TDC problem is discussed in another thread. Short version- a few degrees after TDC minimizes the risk of kickback and doesn't seem to have any downside. A workaround to get later timing is described in the other thread. However, it would be better if the ATDC starting timing were baked in. The workaround to get ATDC timing is not in the certified aircraft installation instructions so it is really only available to experimental aircraft.
Would I buy another? Probably. Bill was helpful and honest about the SIM, but even with great customer service, a mag overhaul would have been less hassle. So, to tip the scales in favor, we've got to avoid future magneto IRAN's.
Surefly will likely improve their product if they can work the changes through the certification system. If they can do that, there is even more to like, it goes from a 3 star review to 4 or 5.
1990 RV-3 (now apart, upgrades in the works)
1959 C172 O-360