Dan,
Very good points. The only thing anyone has left out that I can think
of is that the coil, being an auto-transformer is indead polarity sensitive,
seeing as how the coils of the transformer are wound in oposite directions
for positive and negative ground.
About the only thing I can think of on the plugs is that the polarity (hence
direction of current flow) will affect which element of the plug is going to
pit , the electrode or the tang.
Harlan.
-----Original Message-----
From: DANMAS@aol.com <DANMAS@aol.com>
To: mgs@autox.team.net <mgs@autox.team.net>
Cc: barneymg@ntsource.com <barneymg@ntsource.com>; BobMGT@aol.com
<BobMGT@aol.com>; Lawrie@britcars.com <Lawrie@britcars.com>;
ccrobins@ktc.com <ccrobins@ktc.com>
Date: Saturday, August 08, 1998 11:35 AM
Subject: Re: New Coil
>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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