Well a CD ignition is a completely different animal than the stock
(usually) inductive setup. A capacitor is a device that can store alot
of energy, can release it very quickly, and resists changes in frequency.
When in parallel with an electrical device that has a non DC output (like
the 120VAC wall circuit in your house) it will do its best to smooth the
output by charging and discharging continously in time with the frequency.
The larger the cap the better the smoothing or less ripple. You can charge
the cap like a battery and release the energy in one shot if you like. Now
used in a spark ignition system like the MSD, a cap is charged to 400V,
then when the trigger from the distributor comes in this massive amount of
power is released out of the capacitor and into the ignition coil. The
coil acts as a 100:1 transformer and steps the voltage up to 40,000V and
the current is also stepped DOWN a proportional amount (a tranformer has to
have equal power on both sides minus internal losses, power=currrent x
voltage) However we have a problem that is really serious. The output of
the cap drops off very rapidly, very very rapidly, too quickly for an
engine that is idling as the spark lasts about 1/6 of the time that it
needs too. The Multiple Spark Discharge or MSD then repeats this process 6
times at low rpm for every one spark of a regular ignition. Now since the
discharge time of the ignition is only determined by the capacitor, at
higher rpm when less time is needed the spark output falls off until about
3500 rpm and above we see only one spark.
Now an inductive system when it discharges starts off low, then the output
biulds to a peak. This is completely opposite of the capacitive which
starts off high then goes lower. It also holds that one spark output much
longer.
I personally have found that CD ignitions like to run leaner fuel mixtures.
I found in my cars that any raw fuel could prevent the engine from
starting. The good side to this is that a choke is not needed at all if
you live in a warm climate.
I haven't started playing with the ignition in my Dak yet, but it does not
seem to be the greatest (it is fine for stock duty though). The plug gaps
are relatively small showing that not much power is used in the system, and
the engine is set up to run richer than typical engines of yesterday.
Leaner engines need a serious spark to ignite them. (another point here is
that NOx is hard to clean once created and running the engine richer will
lower this amount but will create more HC which is then easily converted
into H2O and CO2 by the cat) Looking at the stock coil it is about the
smallest that I have seen on an American truck or car. This means that
thin wire guage was used internally thus a larger percentage of internal
losses are to be expected. It is also mounted on the block which is
usually a no no due to vibrations (need an epoxy core for sure).
Basically if you keep the engine stock, replacing no more than the plug
wires with Blue Max spiral core or the like would be fine in my opinion.
Then the coil, then the module. If you do the module, get the coil that
was designed to work with it. I would not get a module without changing
many other things first though.
Hope this helps
Nicholas
At 01:01 AM 3/10/98 -0500, you wrote:
>Hello,
>
> What is the CD ignition and where do I get one. How much performance does
>it add. Oh and how much does it cost?
>
>Thanks
>
>chase7@cdc.net
>
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