To the List:
Just thought I'd throw my 2 cents worth in here as I formerly designed
electronic ignition systems for Motorola.
A common misconception is that a CD ignition is a "high performance"
ignition. Acutally, most CD's produce far lower spark energy than
conventional inductive storage types. What CD's do, is produce a very quick,
high voltage pulse that's helpful in lighting oil-fouled plugs. However, the
spark duration is much shorter (usually 10 times) than an inductive storage
signal.
The spark energy is determined by the product of the voltage times the
current times the duration, or the area under the spark pulse.
Lean burning engines (which most should be if they're producing maximum power
and minimum emissions) need lots of spark energy to keep the mixture ignited
under the high turbulence and swirling conditions in the cylinder. High
energy, inductive storage systems are better at delivering this energy than
CDs, usually. Multiple spark systems also have advantages, as they can
re-light the fire if it goes out, but this is done at the expense of total
energy as multiple sparks must now fit into the same spark time as one long,
high energy spark.
After studying and benchmarking MANY ignitions, including magnetos, I
recommend a good, high energy inductive storage ignition. To get high
energy, you usually have to go breakerless as the ignition current at idle is
too high for points to live reliably. Unless you have bad rings and an
engine that regularly fouls plugs (then you really have other problems), you
really don't need the 40KV - 80KV initial spike a CD provides. What's more
important is burn time.....go inductive storage.
OK, I'll shut up now.
Myles H. Kitchen
1965 Lotus Cortina Mk1 #128
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