There's been some questions and answers bandied about as to whether the
stock ignition can perform as well as some of the aftermarket units.
There are so many variables here that there doesn't seem to be one reply
to cover it all. This will be no different, but yet another version.
I dug out my copy of "Tuning Lucas Ignition Systems" published by
Speedsport Motobooks,
Bercourt House, York Road,
Brentford, Middlesex, TW8 OQP,
England.
It was first printed in 1972, and I don't know if copies are still
available. It's a 50 page book, so I won't do more than lift out a
couple paragraphs as may apply to this discussion. To paraphrase...
A four cylinder engine has a dwell angle of about 60 deg., and in order
for sufficient voltage to build up in the primary the minimum time the
contacts to remain closed is about two milliseconds. This means a
practical limit of 8,400 rpms for a four cylinder, and 5,600 for a six
cylinder..unless electronic assistance is provided.
Regretfully, it doesn't say clearly what happens to the capability of
the plugs to fire when these rpms are exceeded. We know the engine does
not hit a wall, like the kind provided by a "real" rev limiter.
It does say this:
If you have made modifications to the engine, like raising the
compression ratio or improving the breathing by fitting new manifolds
and carburetors, you could be greatly increasing the loads on the
ignition system. There could be mis-firing problems, as the voltage
required at the plug electrodes to give a spark increases in direct
proportion to the compression pressure at the spark plug gap.
Not an exact science, is it?!
We know it only takes one spark to fire each cylinder. That's what the
stock system provides. I can't think of why a hotter spark would create
more complete combustion. Once the flame front starts, more or hotter
spark wouldn't add anything. If it doesn't start, you'd hear or feel a
misfire, at least at the lower rpms.
Better mileage would come from a leaner air/fuel mix, possible with
wider plug gaps. Better performance when you add performance equipment,
where the CD ignition can shine brighter than the stock output.
In conclusion (yea!) new car manufacturers have gone to the High Energy
Ignitions. They don't usually make moves without a good reason.
Dick Taylor
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