Certainly the main reason must be cost versus reward. COP solves several of the problems which CDI solved first with distributor systems, but it can't solve all of them completely (IMO). With regard to pencil coils not being suitable. That reasoning would only apply to the CDI aftermarket which might want to mate with some OEM inductive coils. It wouldn't be hard for a car manufacturer or supplier to make coils specific for CDI use. Cheaper actually since they don't have to be high inductance.
An old example of a CDI design being compromised to suit OEM coils is the MSD6A. One of the reasons (this time just my opinion) the MSD6A CDI has that grotesquely long gap of1mS between spark events(other than more time to recharge the capacitor) is that with a high inductance coil and a shorter interval, there can be destructive interference affecting the strength of the second and subsequent sparks. To give time for opposing voltages to ring out, the interval has to be longer. The 1mS interval means that the second spark is only useful at slow idle and all the extra sparks are completely wasted above that. 1mS turns into a lot of crankshaft degrees where nothing is happening. (every 1000rpm= 6 degrees). And yet MSD sold many thousands of these CDIs which only work effectively because of the first spark in the series. Fred
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Originally Posted by M&W Ignitions
Fred
It is not used mainly due to cost and service interval. There is another not well understood problem with COP/Pencil coils when used with cdi ignition due to their less than ideal magnetic properties (simplified) although we have noticed recently the changes to Bosch pencil coils which should reduce/eliminate the problem.
SAAB used cdi originally as it allowed them to more easily implement spark plug ion current monitoring for knock detection however now there are a number of inductive ignition coils with this feature built in such as those used by Haley Davidson.
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