<VV> "Points" to ponder - Pertronix Issues
Padgett
pp2 at 6007.us
Fri Oct 28 08:49:46 EDT 2005
>There are several reasons that all of the car manufacturers changed from
>point actuated ignitions to electronic based distributors, then eventually
>distributorless electronic ignition systems. First was the advent of Smog
>regulations. ..
Actually electronic (aka transistor aka breakerless) ignitions go back to
the period prior to the GM racing ban in 1963. The Delcotronic ignition
intended for introduction for the 1962 model year was a great improvement
over points. That there was a problem had been acknowledged much earlier
and led to the rise of the Mallory Magneto ignition and by the late 1950's
dual point distributors from Delco-Remy were common on high-performance
engines.
The Decotronic consisted of three major elements, an amplifier that had to
be kept cool so was usually mounted in the wheel-well, a magnetic impulse
unit replacing the points in an otherwise conventional distributor, and a
special high-voltage coil. Plug gaps were also commonly opened up .015-.020".
The system placed the amplifier between the 12v source and the positive
terminal of the coil with the negative side of the coil connected to
ground. This meant that a conventional passive tachometer that was
connected to the negative side of the coil would no longer work and a
transistor "boost" circuit was developed so that the tachometer could be
connected to the positive side. If you look at the schematic it can be seen
that the transistor circuit is merely a front end on a conventional passive
circuit.
The Delcotronic was in production until 1966 when it was replaced briefly
by a Capacitive Discharge unit which led the way to the first HEIs in 1971.
These early units had a much smaller diameter (drat, it is hard to tell
this story without illustrations) than the 1973 HEIs which followed as it
was found that 60,000 volts would arc over considerable distanced. These
lasted until 1986 when the first Distributorless Ignition Systems (DIS)
were introduced though the full transition took several years.
So it was racing and high performance that led to the development
of transistor ignitions, not smog. If you get a chance to see any NASCAR
footage of the interior of GM race cars in the 60's and 70's, many had a
pair of Delcotronic amplifiers (if one failed, ignition could be switched
to the other) on the passenger side of the dash.
Padgett
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