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The LSE CDI uses $1.69 NipponDenso
automotive sparking plugs and very high quality, unshielded, silicon HV
leads, unlike the shielded leads used with magnetos. These leads have
distributed resistance which does away with most ignition noise. Usually when
there is noise, it is due to a loose connection, generally at the plug, which
results in some arcing with its attendent arc-discharge radio frequency
spectrum. This noise may also be a sign of arcing through pin-holes in the
wiring to nearby engine structure. Keeping the wires separated from the engine
reduces the voltage pressure across the insulation to mitigate
this punch-through. Wires should be kept clean, too. This goes double for
the "cigarettes" in shielded plugs. They, and the well in the plug, should
be cleaned and never touched by the hands during assembly. Skin oils from
handling can lead to arc-breakdown in the plug, especially at higher-altitude
flying.
BTW, a lot of "alternator whine" takes
place because of a high frequency oscillation which occurs when
the crossover switching from one stator winding to another
takes place. This may be reduced by placing a large value
electrolytic capacitor on the output, or film capacitors across each
winding to lower its resonant frequency. It's also very important to provide a
wide braid conductor from the alternator ground terminal to the engine to
provide a high conductance path for alternator currents. Depending on mounting
brackets for this pupose is not good practice. It's also good practice to
have a braid from the engine to the firewall.
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