fixed timing ei benefits?

after a lot of reading past posts, i think i have good grasp of ei benefits with advanced timing curves and efficiency.

question: if 90% of flying is down low, aerobatics, short flights of 1 hour, does ei really give benefits? if staying rop, i’ll get lower cht and seems like i should stay with fixed timing. pmags require yearly inspection so 500 hour mag maintenance might be only once every 7-8 years.
in a nutshell- no real benefit in fuel burn, not huge benefit in maintenance.
maybe better starting? would you expect smoother engine? i guess a little weight loss and no chance of mag destruction causing engine damage? how often does that create an emergency?

bryanrene said:

not huge benefit in maintenance.
maybe better starting?

Click to expand...

If you're going to stick with fixed timing, the benefits are the much hotter spark, which (1) gives better starting, and (2) allows the use of larger spark plug gaps (some allow auto plugs, saving money) which greatly reduce plug maintenance. Nearly all "mag check failures" are really "spark plug problem".

Electronic ignition (how the spark is generated) and spark advance (when it is delivered) are often conflated, when they are two different subjects. Some of the currently available EI's come with pre-programmed advance which cannot be readily modified. Others offer some degree of user customization of the advance settings. A third group allows a user to pretty much program whatever advance values he deems fit, including none at all...fixed timing, with all the EI advantages.

Mags

Pitts S2B had shower of sparks mags so no impulse. Your S2C is likely the same.

You asked about performance but . . .

(+)SureFly claims a 2400 hr operating time before any inspections rebuilds etc. Reliability (failure rate) not known on this or claimed. If the failure rate for 2400 hrs was 0.05% then that is covered.

(+)It connects directly to the existing mag harness. (-)But - - it requires electricity to work. No free lunch, yet. A small battery could provide back up, but oops . . . maintenance. Seems like no free lunch.

Beginning to sound like a weighting of personal preferences rather than a solid replacement.

Rather than open the "best brand" can of worms, let's go back to the OP's fundamental question.

bryanrene said:

question: if 90% of flying is down low, aerobatics, short flights of 1 hour, does ei really give benefits? if staying rop, i’ll get lower cht and seems like i should stay with fixed timing.

Click to expand...

I've been flying fixed timing EI for the last five years, and experimenting from time to time with advanced timing configurations. I can do it easily because the system I'm running allows entering two separate advance maps, and switching as desired in flight. Plenty of opinions, but to be frank, not many have flown fixed and advanced timing back-to-back while delivering exactly the same spark energy.

Short version: Advance has little or no benefit down low at high power, which seems to be the question asked. In reality, even the systems with pre-programmed advance schedules don't add any advance at high MP.

Moving to the questions not asked, I'd first suggest studying Nigel Speedy's excellent article from Kitplanes, linked below with the author's permission. As you do, please note two things. First, Nigel is a professional test pilot, so I think we can depend on his data gathering skills. Second, it was a parallel valve engine, not an angle valve. The angle valve does not respond to advance like a parallel valve.

The short version? The parallel valve likes advance when running lean of peak. Advanced timing compensates for slow combustion speed.

https://www.danhorton.net/Misc/Nigel Speedy - Ignition Advance .pdf

As noted, the angle valve is different. Speaking specifically of the 390, optimum fixed timing is about 23 BTDC. If using variable timing to go significantly LOP, set the base at 20 per the book, with a max of 30. Personally I've found nothing very useful past 28, and reserve 50~100 LOP operations for low power, low altitude loafing. If I'm going somewhere, it's 23 fixed and cruise in the 8~12K altitude range at peak EGT, Lycoming's economy cruise recommendation.