EI is great but no guarantee of fuel Econ (but likely)
N941WR said:
A few EI questions:
1) How much more power do you get from using an EI system?
2) Does it make much difference if you have on EI and one mag?
One unit gets you the most advantage and the second a little more. The exact percentage is hard to definitively nail down. The 4% and 6% is possible but not guaranteed.
Gains are more complicated, part brand of EI and engine but more how the pilot flys.
Take and economy car for example; if you make jackrabbit starts and always are on the gas or brakes, no in-between, your mileage will suck despite what the EPA milage sticker says.
To realize the percent gains mentioned above (which are near max gains) you would be in cruise at approx 70% or less power. This is where the EI shines, with their spark advance and strong spark. At higher power they have fixed timing like a magneto, but even at higher power with fixed timing, you still enjoy a stronger spark than a magneto, which is very good.
In theory an EI should be more reliable and almost zero maintenance. The down side is they are electronic and require electrical power. The only self sustaining EI is the P-mag. The 4% / 6% mentioned above comes from Lightspeed's website. P-mag does not make any claim of performance gains. However it would be interesting if RV'ers did flight testing between magnetos and all the different brands of EI. I will not say performance is all the same with EI, because they are not, but most buying decisions are because of form, fit and function (aka how its packaged). Technically the Lightspeed III should give the best econ and power. Who knows for sure with out test.
Cafefoundation.org did the only test on EI verses magnetos I know of. They used a Mooney and IO-360 Lyc. The test was with an Electroair EI, both single/mag and dual config's. The Electroair is a fairly representative of an experimental EI, kind of between a Lightspeed and E-mag (report available on their site). They did indeed get some good gains in power and fuel econ. The gains where at the lower power operations like cruise, as I mentioned.
At higher power, even with fixed timing advance, you still get the advantage of a stronger and "fatter" spark (aka longer). Obviously the more gas you burn and not blow out the pipes, the better econ & power.
However at higher power with an air-cooled engine we all run full rich anyway (mag or EI), so there is not much or any real fuel econ gain at 100% power. Bottom line, fuel econ requires you move those little black and red knobs judiciously. EI is not automatically going to save you fuel.
You will see a little more power, however the rest of the engine becomes a limiting factor in making more power. EI only can do so much. You need better cams, pipes, induction and basically a whole new head design, combustion chamber shape for example. How much extra max power can you gain? Who knows unless you dyno it. At least (I'm guessing) 1% or 2% on a 180 hp engine, which is almost 4 hp, not bad. I am aware of greater gains claimed.
Think of EI as putting a CD player in a 55 Chevy.
The real benefit is easier starting, smoother idle and no points to wear out. Magnetos are still good consider they're design origins date back 50 year old, in principle over a 100 years old, mags have racked up an impressive reliability record, not perfect but very good.
EI has a good reliability record, but you have more wires to connect (even e/p-mag). More wires and connections means more failure points. If you take great care with your EI installation wiring and electrical system design, you'll be fine, i.e., magneto reliability or better. Of course that is why they designed aircraft with two ignitions. If magnetos where 100% reliable, they would not have needed two ignitions. My point is know what you are getting. Its not a panacea.
