Quote:
Originally Posted by Terry, NJ
Here again, I'm thinking back to my days in aviation. I believe all the Continental and Lycoming engines had a dual ignition and a four position ignition switch, off, right mag, left mag, and both mags, Prior to take off, we always did a a run up. This involved bringing the engine to 1650 rpm and switching to say, left mag, check rpm (Shouldn't be lower than 1600). Right Mag (Same drop) and then back to both mags. RPM should increase to 1650. So, running on individual mags gave us 50 less rpm. I realize that the purpose of dual mags was not to gain the 50 rpm, but increased reliability and a lessened chance of engine failure due to a faulty ignition. But the dual ignition was a true dual ignition with two separate mags.
Terry
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Terry, the difference is Redundancy vs. Complete Combustion. In an aero-inspired engine, the main intent was to have a back-up plan when the first ignition system failed. In racing and early era engines, even those seem similar by design, the intent was different. The brass-era/early-era vehicles had poor combustion chamber designs, and flame travel across a large bore piston was pitiful, -especially at low RPMs. Therefore having two separate ignition sources from opposing locations within the combustion chamber allowed for the fuel mixture to be ignited nearly simultaneously within the cylinder. This simultaneous combustion allowed the charge to provide a bigger push on the piston creating more power. The racing applications liked the dual ignition because not only for better combustion efficiency, but also the advantage of not needing to have as much total ignition timing. Less chance of detonation caused by too much ignition timing when two ignition systems are firing simultaneously but at a less total advance, especially across a wide RPM band.
Quote:
Originally Posted by johnneilson
Brass era cars had multiple plugs, this is a Buddy's Pierce Arrow Roadster small inline six (540 cu in approx) It has 3 plugs per cylinder, a mag that fires 2 and dist for 1.
Dist is used for starting and turned off once running.
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I would guess the reason for the distributor is the mags were not impulse mags, and so it was easier to start with a battery supplying voltage to a coil. This is one area where a Ford Model-T was really superior to other cars who were using Kettering-based ignition systems. An early Model-T (pre-1920) was provided without any battery to aid in starting. These were started by spinning the engine where the magnets created enough AC voltage to ignite a coil. If the engine oil was thick, it hampered the mag output and made the car difficult to start. The same issue applied to a Kettering-based ignition system, however if someone had a dry-cell battery to connect to the Model-T coil box, then the coils could be fired multiple times with every ¼ turn of the crankshaft. This allowed the spark plugs to be self-cleaning when the engine was overly rich on fuel. A Model-T could be started in the coldest of temps when others could not be started in the same type weather. Henry knew this, and this is just another reason why he felt the Model-T was the perfect car.