By Myles H. Kitchen
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.