Ignition timing ref points

[Todd King]

  <<<   From: Kalle Pihlajasaari <kalle at device.data.co.za>
  Date: Tue, 8 Oct 1996 12:39:54 +0200 (sat)
  Subject: Ignition timing reference points
  ...
  I was thinking of adding a 256 or 360 slot optical interrupter disk into
  my distributor to give double the that number of edges every rev
  of the dizzy (or the same resolution on the crank).  Is one degree
  on the crank accurate enough for a totally digital one or two of
  design for a mapped ignition.  Interrupter disks like this are   >>>
  
  Well again, you can do alot with less firepower than this. Not to imply that 
  this is the only or best way to do it, but for example the GM SFI system on 
  the turbo Regals has a best resolution of only 6 edges per crank rev (3 rise 
  and 3 fall); The Crankshaft Position Sensor (CPS) is just an interrupter wheel 
  that has 3 slots that gives 3 rising (and falling) edges per 360 degrees of 
  rotation. We accelerate the cr*p out of the poor little things (231" V-6; 600 
  hp and 600 ft lbs is pretty easy to get) and things seem to work pretty well 
  without 1 degree resolution ability :-) A cam position sensor is used to 
  reference no.1 cylinder, providing a "blip" every 720 deg. That's it. Consider 
  the real resolution requirements carefully for your design! Just how fast does 
  the crank actually accelerate (and thus throw off the timing accuracy) 
  compared to the number of firing events per rev is a good problem to ponder...
  Best I ever came up with was that down in the 3 timing events per rev scale 
  the crank accel was pretty negligible; 'Course I'd welcome some more precise 
  input on this!
  
  Todd  Todd_King at ccm.co.intel.com