Hi Doug,

It's easy to "know."  Those in fixed pitch prop planes with one electronic ignition and one mag have frequently performed the following test:
- Turn off the electronic ignition in cruise flight.  Wait until rpm and speed stabilize.  Note the drop.  Turn it back on until things stabilize again.
- Turn off the magneto in cruise flight.  Wait until rpm and speed stabilize.  Note the drop.

In virtually every case, the result is more rpm & speed for effectively the same fuel flow running off the electronic ignition.

It can also be done with a C/S prop, but your only indicator is airspeed.

Other observations include smoother running LOP, easier starting, less likely to foul plugs.  All of these are worth something to many.

Blue skies,

Bill Reister

On 14:59, Douglas Brunner wrote:

At the risk of starting a “theological” controversy, I would like to raise some reservations about electronic ignition systems (other than reliability and loss of electrical power)

 

Peak intracylinder pressure (the point in the combustion cycle at which pressure in the cylinder is highest = effective timing) is related to 3 things; spark timing, rpm and MIXTURE. 

 

Why mixture? Because air and fuel mixtures burn at different rates depending on how rich or lean they are.  So at a given RPM, MAP and spark advance you can vary your effective timing by changing the mixture. 

 

·         Want to advance your timing? Change your mixture to a 50 deg ROP mixture – which is the fastest burning.

·         Want to retard your timing?  Make your mixture richer or leaner from 50 deg ROP.

 

And since optimal power is achieved at an effective timing of 16 deg ATDC, advancing the spark timing may or MAY NOT increase horsepower depending on the mixture.  But advancing the timing will likely increase the magnitude of peak intracylinder pressure leading to higher intracylinder pressures, higher cylinder head temperatures and greater stress = shorter enging life.

 

For those of you who are using electronic ignition (I am not):

·         Are you sure you are getting more horsepower?  How do you know?

·         If you are getting more horsepower, are you getting it during all modes of engine operation?  Rich of peak, lean of peak, high MAP, low MAP, etc

·         What is happening to your TBO?

 

D. Brunner

 

The biggest advantage of any of the electronic systems (in my opinon) is that they provide a spark advance that is a function of at least manifold pressure, giving an advantage any time the manifold pressure is much lower than maybe 25 inches.  But there is very little combustion taking place in the exhaust system regardless.  The reason the exhaust temperature rises is that more of the combustion occurs after TDC and that means less of the energy is being converted to work.  The down side of advancing the spark is that since more combustion occurs at the highest cylinder pressure, more heat is transferred to the cylinder head and piston.