Combustion chamber & twin plugs

[Pat Hines]

When I was flying the mag check usually produced about a 100rpm drop,
sometimes more for one than the other.  Dusting off my memory, the check
was pulled at either 1500 or 1800rpm.  The twin plugs and twin magneto's
were for reliability since early ignitions, particularly points and
coils were notoriously unreliable.  Later as engine size grew it was
notices that the secondary benefit was increased power if the plugs were
properly placed.

     For example the engine in the Cessna 172 that I flew was a Lycoming
O-320.  A 320 cubic inch four cylinder engine with a single updraft
carb.  Since each cylinder was eighty c.i. the twin flame fronts in the
combustion chambers produced more power by burning the fuel air mixture
more thoroughly.  More smoothly as well because the double flame fronts
reduce the opportunity for detonation of unignited fuel.  This
detonation occured because the piston is still traveling up the bore
when initial ignition happens, crowding the unignited fuel air mixture
to one side of the combustion chamber, causing low level detonation.

Pat
-- 
"Reality is meaningless, perception is everything"  PH