Gerry,
I agree with your statement concerning modern ignitions. In fact I
believe some are wired with two plugs in series such that one is
positive and one is negative.
Remember, though, that or much loved British iron, although modern when
compared to the Model T's buzz box ignition, is very low powered
compared to the electronic ignition of today. The points are the real
limiting factor although I think coil design may have also been an issue
when the cars were built. The amazing life of spark plugs in modern
cars is from two factors. Improved materials is one but plenty of
voltage also comes into play. If one were to open our plug gap from
.025 to .040 you would see a degradation of performance. Modern
ignitions would probably fire a plug with .100 gap and still light a
beer sign.
Because of this, I believe that it is important to reverse the coil
along with the ammeter and the battery (and flash the generator) when
you change polarity. Although the car will still run, without, you will
lose part of the already narrow safety margin on available spark.
Another possible polarity sensitive component (say that five times fast)
is the fuel pump. If your SU is original (Hah!) you have no problems.
Newer units have a capacitor across the points (much like the ignition)
to aid point life. These are somewhat polarity sensitive. Later still
units have a diode across the points and have better still longevity.
These will not work at all if you reverse the battery. BTW, I don't
think a diode protected positive ground pump was available at first and,
since the negative ground units were cheaper than the real positive
ground units, some suppliers were making positive ground pump by cutting
the diodes out of negative ground pumps and changing the SU tape. These
work but have terrible points life.
As far as the regulator goes, maybe changing the polarity will reverse
the metal deposition already done and actually extend its life!
Since I have enough complication in my life already, the MGA has stayed
positive ground, generator, and points equipped. No radio or other
sissy stuff required. The XK coupe will probably have a modern
electrical system since its purpose in life will be different as a long
distance tourer. I am even considering adding (oh, the horror and the
shame!) air conditioning. When will the madness end?
Regards,
Bill Eastman
61 MGA driver
58 XK150 fhc project
A Morgan is next on the list but, at this point, may put me on "a list"
as far as my wife is concerned.
>>> Gerry Willburn <Gerry.Willburn@trw.com> 05/04/99 03:50pm >>>
<snip> but in actual fact it makes little difference
in actual performance. Modern ignition systems have sufficient voltage
that you will get adequate performance without worrying about polarity.
If you reversed the wires on the coil you most likely would not notice
the
difference in performance. <snip>
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