At 03:42 PM 1/28/2001 -0700, Phil Bates wrote:
>....
>Barney Gaylord - chime in on dual point distributors and power at this
point, ....
Nothing terribly different about the purpose and end function dual points
distrubutor. It makes and breaks the primary coil circuit same as the
single points dizzy. All of the same rules apply for spark advance curves.
The main claim to fame of the dual points dizzy is that it allows more
dwell time. One set of points is about 8 degrees out of phase with the
other set. Any time either set is closed the coil is charging up, and only
when both sets are open does it fire the spark. The result is that the
points circuit stays closed more and open less time, so the coil has more
time to charge up. This can give a stronger spark at high engine speed.
It also splits the electrical load between two sets of points, so they may
last a little longer. However, most of the arcing is going to occur when
the last set opens, so the trailing set is going to burn and wear almost
the same as the points in a single points dizzy. If you were cost concious
you might change the trailing set twice before changing the leading set once.
One small advantage (and possible disadvantage) is the redundancy, such
that if one set gets burned and stops conducting power (fails open) the car
still runs on the other set, but then the timing may be way off. Since the
trailing set controls the spark timing, if that goes open circuit, then the
leading set fires the spark too early. If the leading set fails open the
dizzy effectively reverts to a standard single points setup. If either set
fails closed you get no spark, so this actually increases the probability
of total spark failure. Not to worry too much about this last point
though. Any dizzy that is badly worn or neglected is more likely to cause
problems, and one in good condition is likely not to cause any problems at
all.
Bottom line is that dual points yield more avenues to problems and only a
little advantage to the average daily driver. KISS is probably a better
idea for most folks. If you want a hotter spark at higher engine speed a
40KV sport coil is probably a better idea.
The only reason I installed a dual points unit was that it was half the
cost of a new Lucas dizzy when I needed one. Now considering how much I
drive the car, and how much the Mallory tune up parts cost, I'm not sure it
was any real cost savings in the long run.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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