Delta Juliet wrote:Starting is much improved as the electronic ignition gives a 1/2" spark which is independent of engine speed. At low speed the system changes the ignition to about 0 degrees advanced (compared to the fixed 20-25 degrees of a magneto). This prevents kickback.
Impulse couplings do the same thing. Electronic spark is typically strong (as noted) and that would the (only) difference for starting if the engine type otherwise has impulse couplings.
Delta Juliet wrote:At speed, the ignition is advanced depending on the rpm and manifold pressure. At full power I never noticed much difference, but when leaned and pulled back in the cruise 20"MP/2100rpm there was a big difference in airspeed compared to std ignition. The system advances the spark up to 40 degrees which makes the engine much more efficient. The advantages are better starting, 10-15 kts extra cruise (135 vs 120kts) and the ability to use Iridium car plugs at £36 a set of 4.
No mention of the altitude here, but given only 2100 rpm it might imply low altitude. In that situation, throttled way back to max range cruise (ie 20 inches MP) you'd see similar advantages to unavoidably running low MP at altitude. Works for a very high powered aircraft. However, if you don't run extremely low MP on a given aircraft the spark will not be advanced to the same degree, and so the advantage will not accrue to the same degree.
For example, if (like some people flying relatively low powered aircraft) you fly around with almost full throttle at low altitude, you'd probably see no benefit - because that's what standard mag timing is spec'd for.
135 kts versus 120 kts takes about 40% more power by rough calculation, so assuming the same fuel flow its equivalent to saying that advancing the spark for max range cruise provides 40% improvement in SFC.