frstnflt wrote:1. Is there a real world performance or fuel mileage benefit? Longer spark should mean more complete combustion?
2. Hot starts any easier? (IO-520D)
3. What is a typical delta in cost vs overhauling a mag plus labor for conversion? [Surefly]
4. Significant draw in current on electrical system?
5. I'm not big enough to hand prop mine but would it be harder to start if dead battery?
I don't have a Surefly, but I do have dual EI on my IO-520D, so take my comments more as generic for EI vs. specific to a particular type of EI (I'm using an SDS ignition system on my Cyclone 185).
1. Yes, but it will be hard to make up the install cost in fuel savings. My home airport is at 5000' MSL, so I'm most often flying in the 6-10k MSL range, so I get more of the benefit of advanced timing; while my advance is user select-able, I have it set up pretty close to what Surefly does: matches Continental's timing above ~25" MP, and peaks around 26 deg advance at reduced MAP settings, which I see at WOT where I am. That is fairly conservative on the advance, so Surefly may go a bit farther at certain settings. Flying LOP, for the same fuel flow as dual mags, I get 2-3 knots better cruise; not a big power increase. Engine was smooth before the swap; engine is still smooth. It is smoother at idle, and will idle at a lower RPM, but that's not really beneficial in flight.
2. No change in ease of starting (cold or hot), with one exception: kick backs. My main motivation for the swap was the dreaded kick-back, broken starter adapter scenario, which I experienced on flight two of my newly installed MT prop. Here's where the SDS may differ, but it needs the prop to spin through a few revolutions before it fires the plugs, and it fires 5 degs after TDC, so no chance of a kick back. This was my primary reason for the change, and am very happy with how it starts now.
3. Don't have Surefly, so I'll defer on this one.
4. About an amp per ignition when running. I already had a dual battery/backup alternator setup, so I wasn't concerned about becoming 100% dependent on electric power.
5. I don't know how Surefly works specifically, but with my system the engine cannot be hand propped since the engine has to make several rotations before firing. This wasn't a concern because since my ignition is electrically dependent, if I have to hand prop, I don't have the reserve power needed to ensure a safe landing should I loose my alternator (unless I ran on the ground long enough to recharge the battery, but I try to avoid that with a dead battery since it is better for the battery to have a more controlled recharge from a completely drained state, or the hand prop requirement is from a starter issue vs. dead battery). Additionally, I built in redundancy with the ability to start the engine on either of my dual batteries.
Sorry a lot of my info won't be a direct comparison coming from experimental, but I'm very happy with the way my 520 runs on EI and again my primary reason was to minimize the risk of a kickback.