QUOTE(Mountain914 @ Jul 6 2003, 08:10 AM)
... I used to run a twin-plug Hemi for a short time. Did Porsche do the twin plug for the same reason, to improve spark / fuel ignition and provide redundancy should one plug not spark in the cylinder? OK - probably a dumb question, as why else would you do it. Or... was it due to the design of the head?
early Porsches used hemispherical head designs. small displacement, high compression, the combustion chamber looked liked an orange peel with the high-domed pistons needed to achieve the racing standard 10,3:1 compression...
so - to improve flame travel, due to the CC design, a second plug was used. made it possible to take about 15-deg out of the spark advance.
for endurance racing, the additional reliability was a plus, i'm sure - not just for the plugs, but for the wires and CD boxes.
the slightly earlier 4-cam engines also used twin ignition, IIRC without CD.
aircraft engines use twin ignition almost exclusively for redundancy - they have huge combustion chambers, and low compression.