A Moment of Clarification!
Bill,
To Clarify (Not to Argue or Disagree!):
The reason a P/E-mag-equipped ENGINE is heavier than a dual-electronic-ignition-equipped ENGINE is that the P/E mags add 6+ pounds TO THE ENGINE, and the dual ignition crank sensor(s) plus the coils only add 2 to 3 pounds TO THE ENGINE.
The weight of a complete dual electronic ignition system, without a backup battery, is between 4 and 6 pounds = 2 to 3 pounds for control/ignition boxes (and associated wiring) installed IN THE AIRCRAFT's FUSELAGE plus 2 to 3 pounds for the crank sensor(s) and coils installed ON THE ENGINE. A dedicated backup battery adds another 4 pounds IN THE AIRCRAFT's FUSELAGE. In other words, the weight of a complete dual electronic ignition system, including a backup battery, is 6 to 7 pounds installed IN THE AIRCRAFT's FUSELAGE plus 2 to 3 pounds installed ON THE ENGINE = 8 to 10 pounds total contributed TO THE AIRCRAFT's EMPTY WEIGHT. Yes, in terms of AIRCRAFT EMPTY WEIGHT, a dual electronic ignition system, including a 4-pound backup battery, only saves maybe 1 or 2 pounds over a Bendix-mag-equipped aircraft (if that!) and weighs about 2 to 3 pounds more than a dual P/E mag system.
AIRCRAFT WEIGHT & BALANCE (MOMENT) is another story, though. The real "PLUS" for a dual electronic ignition system is that most of its components are distributed in the fuselage instead of bolted to the heavier, angle-valve engine. 2 to 3 pounds of control/ignition boxes and wiring are installed in the fuselage BEHIND THE ENGINE which is a positive contribution in terms of balancing a heavier engine. More importantly, the builder can locate the 4-pound backup battery ANYWHERE ALONG THE LENGTH OF THE FUSELAGE to tailor/improve the aircraft's moment and, thus, balance the heavier engine.
With a dual electronic ignition system, the builder can tailor the moment contribution for the heavy engine+dual electronic ignition system+composite prop combination to match, or nearly match, the equivalent moment contribution of a dual-mag-equipped 180hp/Hartzell engine. In this way, an RV's control feel with a heavier, angle-valve engine can match, or nearly match, that of an RV with a dual-mag-equipped 180hp/Hartzell engine which is generally accepted by the RV community as the "ideal" combo for an RV-8/8A, right? On the other hand, maybe a dual-P/E-mag-equipped 180hp/Hartzell combo is even better in terms of control feel? (I don't know!)
Note: The backup battery "cables" are only No. 18 wire. Each control/ignition box draws less than 1.5 amps continuous (less than 3 amps total). The backup battery is only a 5AH battery. In other words, the weight of the dual electronic ignition's wiring, including the backup battery "cables," is fairly small; on the order of half a pound, if that.
Well, anyway, in terms of compensating for a heavier, angle-valve engine and maintaining the great RV control "feel," it still seems like a dual electronic ignition system is the best ignition option, at least at this point in time. Of course, the weight savings and moment improvement associated with a lightweight composite propeller are even more important. Compared to the P/E mag option, the dual electronic ignition system is heavier and more complex in terms of installation, but that's also its main advantage in terms of compensating weight & balance for a heavier, angle-valve engine.
Again, it's all just my "2 cents," and that's about what it's worth! (. . . just trying to help a fellow builder!)
Best Regards,
Bill Palmer
![Roll eyes :rolleyes: :rolleyes:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)