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Part# 08-17074
MFR Model# SIM4P


Now approved for many turbocharged twins and most 4- and 6-cylinder Continental & Lycoming powered aircraft.

Note: Surefly strongly recommends the customer purchase a NEW slick-style harness and fresh spark plug set with every SureFly SIM.

The vast majority of 4-Cylinder applications will replace the impulse coupled magneto. 4.4 lbs.

SureFly is an FAA certified electronic (solid state) magneto replacement. The SureFly Ignition Module replaces one magneto - generally the left or impulse-coupled/starting magneto on most aircraft. 4 and 6-Cylinder models are available for Lycoming and Continental engines.

Replacing just one magneto eliminates magneto maintenance and cuts associated costs in half! Zero maintenance. Zero rebuilds. Zero overhauls. Most fixed-wing single engine aircraft can enable SureFly's advanced timing feature for improved cruise flight efficiency. Many other aircraft will be able to use the advanced timing feature as the FAA extends SureFly's Airframe STC AML.


For SureFly customers, 500 hours is simply not good enough. SureFly Ignition Modules provide operators a 2,400 hour operating service time. No inspections, no rebuilds, no overhauls. That prevents scheduling headaches and down time. That saves money. Period.

SureFly Ignition Modules have no mechanical parts that wear and all solid-state electronics. There's no need to disassemble a SIM like a magneto every 500 hours - which eliminates the chance of introducing a maintenance related failure.

SureFly Ignition Modules deliver a more consistent spark energy with higher accuracy than traditional magnetos. Variable timing advance provides SureFly customers real fuel savings. Low power consumption and light weight (up to 2 lbs. lighter than a Bendix magneto) make SureFly Ignition Modules light on fuel and light on the wallet too.

Better Starts
SureFly perfectly controls timing at TDC below 400 rpm which combined with longer spark dwell and the option to use wider gapped spark plugs, makes starting a breeze, greatly minimizing wear and tear on high performance starters and electrical systems.

SureFly Ignition Modules are hand built in Granbury, Texas almost entirely from components manufactured in Texas and Michigan. Designed, engineered, created and supported by the same team that brought you Sky-Tec starters and Plane-Power alternators, our approach to SureFly shares the same commitment, experience and passion for creating and bringing sensible, affordable solutions to the piston engine aviation market.

With the low cost of the units, combined with SureFly's potential fuel savings and low maintenance/replacement costs, there is simply no better value in magneto replacements for Lycoming and Continental engines.


  • Aviation spark plugs – gapped .016 to .036
  • Slick style harness – Shielded aviation harness
  • Input voltage 6-30 volts
  • Avg. Current @2700 500mA
  • Retards spark to TDC for starts
  • Up to 38 degrees Ignition advance – RPM & MP based
  • Hall Effect sensors provide velocity and position input
  • Manifold pressure sensor range – 6-74 inHg
  • Operational temp range -35 to 250 F
  • Minimum MTBF 2000 hrs
  • No interval inspections
  • RPM range 0-3500
  • Voltage to bridge .036 spark plug gap
  • Minimum 35mJ spark energy
  • 50mJ nominal energy


    Intelligent Timing Advance
  • For non-turbocharged engines, SureFly controls spark advance up to 38Ί before TDC as determined by manifold pressure and RPM (engine power setting). Each engine's base timing advance is read off the data plate and set into the SureFly Ignition Module or, "SIM" at installation. The timing advance schedule is hard set at the factory, when the SIM is manufactured, to provide the highest possible combustion efficiency.
    No Mechanical Points
  • Not only are points and condensers a point of failure in magneto ignitions, so are rotors and caps as they carbon track and provide alternate paths to ground as resistance builds in the system. That's why SureFly utilizes none of these antiquated technologies. SureFly components are all solid state and industrial-grade electronics.

    The result is zero maintenance, zero overhauls, no rebuilds, and no maintenance costs whatsoever! Nothing to wear. Nothing to maintain. Run it to 2,400 hours of SIM operation.


View the latest eligibility chart at Application Guide

If any of the following items apply to your installation, please call SureFly at 817-373-5161 before proceeding with the purchase or installation of a SureFly Ignition Module:
  1. Your aircraft tachometer is one of the following:
    1. Horizon,
    2. Electronics International,
    3. EFIS or Engine Monitor that requires magneto P lead inputs,
    4. EFIS or Engine Monitor that requires a 0-5 volt square wave input,
  2. Your aircraft has more than one engine,
  3. Your aircraft has an existing electronic ignition,
  4. Your aircraft has one of the following STC’s:
    1. Western Skyways Turbo STC,
    2. Spin-on oil filter adapter,
    3. Auto Fuel STC.
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Installed the SIM4P on my 1946 Cessna 140 with new ACS ignition harness from Spruce....initially had issues at high RPM when the ignition was isolated on the SIM4p...after fully troubleshooting the system it turned out to be the brand new ignition harness....put the old one on and was good to go. Starts are great. Engine runs strong and smooth. Talked to the surefly support person several times and got good solid information. Seems like a worthy upgrade. Talking to the tech after we isolated the issue it sounds like they have a fist full of new ACS harnesses that did not work out of the box. The tech says they have had the best luck with Champion and and Kelly Harnesses.

Dave K
February 25, 2021

*not paid by surefly at all, but rave to everyone about this. 10 Stars! Surefly will put slick and bendix out of business. Have a well kept Cherokee 180 had a hard time starting hot. Mags only had 200hrs, replaced left with this one and BAM! starts every time very easy! No matter how hot it is. Runs smoother, gets better fuel economy and has more power. Cruises about 5kts faster at a lower fuel burn. ~115kts @ 7.5gph now vs 110kts @8.5gph Best money Ive ever spent on the plane.

September 4, 2020

I like it! Ran rough in the beginning because harness Springs needed a little stretching to make contact with the Sim, but once everything is working as it should it’s a great product,, the plane runs as good on it alone as it does on both regular mags 👍👍👍

August 19, 2020

I’ve flown with electric ignition in a Long-EZ for years and was wondering when it would show up for certified aircraft? Had a mag fail it’s 500 hour inspection and it was less expensive to go this route rather than repair. Surefly is super easy to install, about as simple as a traditional mag. I have an EI tach and it required removing the current resistor and replacing it with an 18 ohm version. Tech support was friendly and helpful! No wonder Lycoming is picking up this product.

Vaughn D
July 7, 2020

Well made product, simple to install and easy to set the engine timing. Engine performance seems to be better and smoother. Like the feature to use the existing ignition harness and spark plugs.

Mike G
June 30, 2020

Installation took some additional time as we had to use the alternate positioning of the gear onto the SIM shaft to enable engine timing. Initial starting was about one full turn of the propeller. Fastest start in over 10 years of ownership!

James H
May 3, 2020

It went on easily, the extra spark really made a difference in starting on my IO-390 with fine wire plugs. Maybe its a bad thing to not have to learn the most perfect possible way to set up a hot start, but I sure like the fact that it will just start now. Like learning to do rolls in a Pitts, vs. a Citabria… learn more technique and theory with the Citabria, but the Pitts is just easy and fun. I have it in fixed timing mode, but will try the advanced (variable) timing when I figure out how much the proprietary algorithm changes the timing. Im a bit paranoid about getting the CHTs up on climb out or high cruise. I think its an awesome replacement for an impulse coupled mag that is almost due for inspection/rebuild.

Customer O
February 1, 2020

Read somewhere this mag wont work with horizon tachs there is a reverse polarity issue, also need a cylinder head temp guage per the stc if you want to take advantage of the advance timing feature. Still looks to be better then standard slick mags though at this time.

Phil S
June 30, 2019

Long story, so here goes: My plane has a 24V battery in the tailcone, and the Surefly has to be connected to the battery side of the battery contactor for the STC to be valid for the installation. (This is because if the battery contactor fails and you lose the power bus, the Surefly still runs the engine off the battery) As 24V AGM batteries are in the $700 class nowadays and there is a (albeit small) leakage current on the Surefly when the engine isnt running, and leaking current kills batteries, I heeded the advice from Skip Koss from Concorde and put in a fuse holder in the instrument panel that would let me disconnect the Surefly power from within the cabin to shut off the power when I wasnt flying. The trouble is that would leave an unfused length of wire from the battery to the instrument panel. So to ameliorate that, I put a 15 A fuse in the fuse holder in the tail and left the 10A fuse in the panel. The Surefly was then installed at the annual, and I left in the original plugs and harness, even though Surefly recommends replacing both the plugs and harness when installing the Surefly.. Ran great, seemed to climb better, and I definitely got book speeds in no-wind conditions in cruise. But there was an oddity: during climb between 8500 to 10,500 the engine would balk unless I used full rich mixture. Huh. Weird. Well, they DID say to change the plugs and the harness. So I changed the plugs to an New-Old-Stock of Autolite UREM38Es I bought 16 years ago when they were $9 each. Well, that made matters worse. Now the engine was skipping randomly, losing 100 to 150 RPM, then surging. Happened in climb, cruise, and descent, once even when I was on takeoff and only 50 feet off the ground. Very sphincter-puckering moment, there. Egads, was it the plugs? Harness? I thought maybe there was some momentary bridging of the electrode gap, so I widened the plug gap. For one flight that seemed to work fine, but the intermittency came back a week later. Gads. So I changed the harness with a new Champion (the old one was the Aero-Lite that I put on 9 years ago) Nope, same problem where a full-power runup on the Surefly magneto alone would have a 200 to 300 RPM drop in the runup, then seem to work fine, and Id see 100 RPM drops in cruise when both mags were on, then surge again when the ignition kicked back on. An in-flight mag check saw a 200 to 300 RPM drop on the Surefly alone, and running fine (no RPM drop) on the right magneto. On two flights I had 6 misfires between initial climb and turning to the downwind leg, so I just came back to the airport on the right mag. While all this was going on I called the Surefly tech line many times, and Bill and Tom were paragons of patience and good advice. I was all set to pull the mag and send it back to verify it was working, and Bill convinced me to do a pull test on all the electrical connections from the battery to the Surefly, check the engine ground strap, and to check the P-lead grounding on all ignition switch positions with an ohmmeter. (The Surefly installation LED blinks the code for the advance timing settings whenever power is interrupted, so if an intermittent occurs in the power wire, it would show up on the LED). So I removed the 10A fuse from the instrument panel, moved it to the fuse in the tail cone, and re-did all the crimp connections for the power wire, then yanked each lead while watching the LED. Another odd thing happened when I pulled the 15A fuse out of the inline fuse holder in the tail cone, namely, the fuse just dribbled out, Normally theres a spring that holds a small preload force on the fuse to ensure contact, but it seemed like there was little or no force on the fuse when I pulled the 15A fuse out. There WAS spring force on it when I reinstalled the 10A fuse, so its possible the brad inside the fuse holder cocked a bit when I put in the 15A fuse just enough to keep the preload off of the fuse, thus making and intermittent/poor electrical connection. Subsequent pull test on the wires never got the LED to blink, so that confirmed the power was rock-solid to the Surefly. The first runup had a bit of a stumble, but seemed to clear up with a high speed runup (like a typical fouled plug) and next test flight ran perfectly. The hiccup where I needed full rich mixture from 8500 to 10,500 was now gone. and I got up to 12,500 with relative ease. So, upshot after this long story: Yes, it works. According to Bill at Surefly, the spark advance starts when manifold pressure falls below 24 inches of MP, so power wont fall off with altitude as much as it does with the constant-timed magnetos, so rate-of-climb will be improved and, in my case, I get actual published book speeds even though my plane was in a major accident in its youth. BUT: make sure you get it installed right! Sometimes even the little things can bite you on the rump and affect how it all works. Mine seems to be running fine so far. Hopefully your installation will learn form mine and will go a lot smoother. Best of luck to all. Happy flying.

Cutlass G
June 8, 2020

My partner and I recently replaced the Left (Impulse) magneto in our 172N with a 0360 Lycoming and twin Slick magnetos. The installation instructions were clear, accurate, and the results are essentially as advertised: smoother idle, easier starting (especially hot-starts), and a notably smaller drop in rpm during run-up. However, it was during the run-up that an interesting trait of the electronic magneto made itself known: During the run-up, when rotating the ignition switch from R to L, there is a brief but distinct POP apparently from the exhaust, similar to a slight backfire. The POP is considerably more pronounced when performing a magneto check in lean cruise, and probably such checks should be avoided. The POP happens every time the switch rotates from R to L and at no other times. Its obvious the anomaly occurs the instant the L mag is turned on during the R to L motion of the ignition switch. The actual POP, I suspect, is due to the L magneto initially providing a retarded (25 degrees from the normal advanced setting) spark because it doesnt yet realize the engine is running. The retarded spark ignites an overly rich mixture which is still burning by the time the exhaust valve opens, hence the POP. Again, probably not an issue under normal run-ups, but at altitude under load Id have some concern over the exhaust system. I spoke with Bill at SureFly about this and discovered Im not the first to have noted the issue. SureFly suspects the cause is due to the design of the ignition switch along with the 100 milliseconds it takes the SureFly to actually produce a spark after it is ungrounded. Their thought is this delay results in an instant between R and L during which neither magneto is operating, thus causing excess fuel to accumulate in the cylinder. The L magneto then ignites that rich mixture with the POP being the still burning fuel when the exhaust valve opens. SureFly is currently attempting to get FAA approval for shortening that time from 100 milliseconds to 1 millisecond. Perhaps that will address the problem. That said, when rotating a perfectly good ignition switch from R to L, there is no point where both magnetos are grounded. In fact, the L magneto becomes ungrounded (turns on) well before the R magneto is grounded (turned off).

Leon L
May 8, 2020


Q: Mooney utilizes the shower of sparks system and does not have an impulse coupler. Would I buy the Sim4p or the Sim4N?

A Shower of Sparks system would be replaced by a SIM4N. As a side note, that is a Bendix magneto and will require the installer to change the spark plug harness with one that mates to a Slick magneto. All SureFly units mate with Slick style harnesses.

Q: Regarding the Surefly: Do you need to change spark plugs or still use the aviation ones? How do you save fuel with this?

Per Surefly: With any of the SureFly units we recommend the owner stay with whatever plugs are approved for that aircraft. They work just fine with auto plugs in the experimental world, so the unit itself doesn't care. Fuel savings are dependent on the aircraft and the operator. Lots of variables there. In general, we might expect some savings when running lean of peak at cruise. The biggest advantages are NO MAINTENANCE and easier starting.

Q: So I do have a Horizon electronic tach which I really like as it shows the performance of both mags. So if I use this to replace one Mag , how will it interface with my Horizon tachometer? Thanks

At this time, the Horizon tach is not supported with SureFly. It is in the works, stay tuned.

Q: Is there a Horizon tach fix yet?

At this time, the Horizon tach is not supported with SureFly. It is in the works, stay tuned.

Q: Do you have to replace both magnetos on Lycoming engines when installing a SureFly SIMP4P?

No, you do not.

Q: Can you replace both mags with the sureflys?

Per surefly: On an experimental, yes. However, you have to have a back up battery system. If you wish to proceed with dual mag replacement, please contact Surefly tech support to be sure installation is done correctly. If the aircraft is certified, you can only install one mag.

Q: Is everything shown in the Hardware Kit drawing included with the Surefly SIM4P unit?

Looking at the Hardware Kit drawing: Everything that is a dotted outline is not included. The remainder of the items listed are either already on the SIM4P or in the installation bag that comes with the SIM4P.

Q: What slick harness would I need to order? I would be replacing my bendix mag with the surefly.

This will depend on your engine make and model, spark plug barrel size, and if you are replacing the left or right mag. With this info, use the slick by champion application chart to select the harness needed for that application.

Q: slick makes different harnesses for my engine based on the model of the magneto. telling me to use their chart does not help. what model slick magneto does surefly copy?

When using the Slick by Champion Harness application chart, you will need to first select 5/8 or 3/4 barrel, then find your engine, Slick mag model, then left or right harness. Example: 5/8" barrel plugs, Lyc O-360-A1A, narrow deck. The first three columns of the mag models are for Slick, and this application has an "X" for the M4006 harness kit, left is M2983 and right is M2984. If you replaced your right mag you would want the M2984 harness, or if you did the left, you would want the M2983, or if you replaced both then order the kit M4006.

Q: Lycoming in the process of releasing engines with the surefly mag. Its my understanding that an engineering change was made on the surefly to upgade/change the bearings to comply with Lycoming reliability requirements. My question is, did surefly make this change across the board to all there products or just the ones that Lycoming will be using?

The units are identical except for color and some difference in the firmware. Bearings and all the mechanical parts are identical.

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