Steve, Chris,
To really discuss this subject rationally, we need to recognize that
"voltage" is not a unit of energy. So comparisons of various components on
the basis of voltage is very misleading. To start with, all coils generate
enough voltage to arc across the spark plug gap, at least up to about
4-5000 rpm; and this voltage is way below 10,000 volts. So the open-circuit
maximum voltage is really a moot point. The parameters of the discharge we
are interested in are temperature and duration which relates to total
energy, or power and duration. From an electrical point of view, the two
parameters that affect this are voltage and impedance. Since we are talking
about a very fast transient, the parameters of impedance, the capacitance
and inductance of the ignition circuit, play a major role as compared with
simple DC resistance. Once the arc is initiated, the resistance across the
spark plug gap drops to a relatively low value and the current flow is then
dominated by the impedance of the rest of the circuit, primarily the coil
and the spark plug wires (and/or the plug resistance with resistor type
plugs) in a standard ignition system.
Having said the above, it is true that some coils, whether we call them
"high voltage" or "high energy" can deliver more energy in the discharge
than others. I can also believe that some form of electronic points would
improve this capability over mechanical points, since the current that can
flow through mechanical points is limited from a practical standpoint by
arcing. Thus, a coil that took advantage of an improved current capability
of an electronic ignition system could theoretically deliver more energy in
the spark. I believe this is what is being alluded to in some of your
statements. The other approach, which Steve points out is fundamentally
different, is to get a "FAT BOX" like an MSD unit. These units provide much
higher energy in the discharge without necessarily changing the coil. I
believe they also provide a more constant output to higher rpms than
conventional ignition systems that decrease in output essentially linearly
with rpm.
In my case, I installed an MSD-6 in my Tiger in 1986 and have been very
happy with its completely reliable performance. This unit replace a "Tiger"
CD ignition unit I had installed about ten years earlier. I can't really
say I experienced any noticeable difference in going from the single
discharge CD to the multiple discharge MSD unit, but the switch from
conventional to CD ignition was quite dramatic.
Well, this is probably more detail than anyone really needed, but I feel
eversomuch better now.
Bob
At 10:13 PM 11/11/98 -0800, Steve Laifman wrote:
>Chris,
>
>I totally agree. But, there is "low and high" voltage coils, and "high
>energy systems". It's just that the Ford HIGH ENERGY unit was being
>discussed, and this in the difference between, say 10,000 volts for a stock
>unit vs. 15-20,000 volts for a "hot coil", available with any of the units
>discussed, and the 40,000 to 80,000 volts and up of a HIGH ENERGY system that
>requires a BIG BOX. they are a different beast entirely.
>
>Steve
>
Robert L. Palmer
Dept. of AMES, Univ. of Calif., San Diego
rpalmer@ames.ucsd.edu
rpalmer@cts.com
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