Dwell and HEI's

[bruce plecan]

As it was explained to me at GM training, and subject to design
changes, and brain fade this is the case for GM modules.  As
used in distributors, not DIS.  The classes refered to are for
the earlier conventional HEI's, circa 82-92,  None/All/Part
of this may be true for some of the newer systems and/or
DIS but I have no first hand info..  
4 pin module  2 for reluctor, one power, and one coil ground
      advance curve contolled by vac/cent devices,  variable
      dwell (but fixed coil saturation time)  if wires are switched
      at reluctor, may have rpm retard, or rpm advance.
      (Again of the top of my head I think it was 2d/1000rpm)
5 pin never have seen one in use that I recall, but have seen
   picture of it.
7 pin the same as the above but with ecm control of the timing
  signal.  the ecm controls the trigger signal but the rc circuit
  is in the module, so reguardless what you do externally the
  dwell will be set by the module.
If you think that the dwell is too short my suggestion would be 
  going to a CD that just uses the module as a signal for the
  ignition box.
IMHO, I think the oem module may have a thermal limitation
  for accuracy.  Hence some people have no problem, and others
  say they are trash.  In my experience using one to trigger
  a MSD, Crane, or Jacobs has always worked out just fine.
  Matter of fact can't think of a module failure or ignition
  miss that wasn't do to something else when run this way.
  In any case 95% of the module failures I have seen have
  been fron rotor burn thru, look at the rotor from the bottom
  side when it starts to discolor, it's time to replace it.  For
  a street/stock/lowrpm not too critical, but on a high
  demand application, when in doubt I change it.  Rotors
  are cheaper than modules.  If you see ANY ultra tiny
  black specks on the bottom side of the rotor throw it in
  the trash or start carring a spare, and dieelectric grease 
  with ya..
Bruce    Never wear a cone shaped hat in a room with
             ceiling fans.  Or outdoors near really low power
             lines, or during lightning storms....