Barney, Bob, Charlie, Lawrie, and others,
Some random thoughts on traditional ignition systems:
1) For a given igntion coil, spark intensity drops off as RPM goes up.
2) If a coil has sufficient capacity to provide a sufficient spark at 5000
RPM, then there is an excess capacity at 3000 RPM.
3) The excess capacity at 3000 rpm is enough to overcome any reduced
efficiency due to reversing of the plug polarity, if indeed there is a
reduction in efficiency.
4) Most "experts" claim there is a reduction in efficiency from using the
incorrect polarity on the plugs. I personally don't know.
5) An ignition coil that will fire an eight cylinder engine at 5000 rpm will
fire a four cylinder engine at 10,000 rpm, all else being equal. That is, the
spark energy *produced* will be the same. Spark energy *required* may be
another matter.
6) Few of us routinely operate our cars in the 5000 + rpm range.
7) Those of us that do, usually will have our ignition system in tip-top
order, including correct polarity of the coil.
8) The ignition coil windings are not grounded to the case.
9) There are three return paths for the spark current to the secondary, and
one of these three paths, albeit a minor one, is indeed the air under the
hood. This path is called "distributed capacitance". We live in a world of
distributed capacitance. That is how the "touch" actuated buttons on an
elevator, for example, operate. The mere presence of your finger near the
button changes the amount of capacitance, as part of the distributed
capacitance normally surrounding the button, seen by the control circuitry.
The solid state control system detects this minute change, and triggers the
doors to open or close, or selects the appropriate floor.
10 )The other two paths are the battery and the ignition condensor. I have
drawn up a JPG file of the complete ignition circuit, if any one is
interested.
11) I don't fully understand items 9 and 10.
12) Race car mechanics go to the trouble of using washers of varying
thicknesses to index the spark plugs such that the electrodes are all pointing
in the most efficient direction. If they go to that much trouble, it seems
that plug polarity would be high on their list of things to do as well.
13) Last week, at the local magazine store, I read article in two magazines
about spark plug indexing. One had a how-to article, and the other said that
indexing was nonsense, and gave no performance gains. Go figure! I haven't a
clue.
14) Barney says the multi coil ignition systems fire two plugs in series. Past
experience with Barney says believe him. Past experience with igntion systems,
and my electrical engineering background, says don't believe him. I think the
operative phrase here is "trust, but verify." I will look into this some more.
Any reference material you can direct me to, Barney?
Enough is enough, so I'll quit now. Have a nice day.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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