<VV> Dual Pertronix!!! - Dual point

[Sethracer at aol.com]

In a message dated 6/17/2008 12:47:01 A.M. Pacific Daylight Time,  
dave.thompson at verizon.net writes:

There  are high performance dual point distributors for street & track.  I
understand that both points are used together to obtain a better spark.  But
what would be the advantage of dual Electronics? Isn't that what  the
electronics are designed to do; give a better more reliable high  performance
spark? Why would you need two on the street? Do Corvair  Distributors fail
that often?

Dave  Thompson




There are a couple of "Dual" Electronics systems for cars. The most common  
is in NASCAR. They run a spec system consisting of a pair of MSD derived boxes  
and dual coils selected by a dash control. The Distributor has a pair of  
magnetic pick-ups installed, each one feeding a box. "Stuff" happens in racing,  
the cost is tiny in case one of the boxes dies, you still finish the race, or  
get pushed into the wall. But the ignition is working! For the Corvair, 
Mallory  made a pair of "dual-point" distributors, then an electronic conversion 
called a  Unilite. With "dual points" distributors, there are two different 
designs. Most  of the systems are designed to use one set of points to energize 
the coil and  the second set to discharge it. One of the sets trails the other 
so for part of  the time both point sets are closed. There is not much 
redundancy here, although  - except for a radical timing change - the car would still 
operate on one set.  Some of the Mallory distributors (for the Corvair) used a 
special three lobe cam  to drive the points. (V8 models used a 4-lobe) This 
allowed a much softer  application of the points. In this design, each of the 
two points  sets fired three cylinders. One set fired 1,5 and 3, the other set 
fired  4,2, and 6. The problem with this setup is you had to check the timing  
advance on two cylinders, first cylinder #1 then Cylinder #2 - which  (in 
theory) fires 360 (crank) degrees  later. To adjust the timing  relationship 
between the two, you had to change the point gap. This was tedious  work, even on 
a distributor machine, it must have been a real pain to do in the  car. The 
redundancy requirements for flight are what drove the dual Pertronix,  not 
performance. It is hard to pull over to the side and readjust your points -  in the 
air. - Seth Emerson  



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