The upper unit fires once per rev as the crank angle sensor runs at half
  e-shaft speed I think. Lynn can probably confirm or deny. The lower unit
  tells the computer when to fire the plugs and provides a handy tach
  signal.
  We need the green wire to give us a sync signal for our data acq.
  BTW this upcoming p-port wave form test is going to give use a million
  times more data than has been previously available on this subject. I am
  not
  exaggerating. Only Mazda may have more info on this subject. In just a few
  minutes, while the engine revs from 1800 RPM to 6,600 RPM, tons of data
  will
  be recorded. 3 data points every 1/1000 of a second. We can see exactly
  what
  the p-port runners are doing as far as pressure waves are concerned in a
  mere instant of time.
  Paul Lamar
  Hello all,
  I need to ask an amateur question...are the crank angle sensors the
  same for the 20B and the 13B engines or do they have different
  internals (rotating wheels, pickups, etc)?
  Thanks much,
  John Bell

  In theory it could be but I am not sure. I have a complete
  stock 20B in the hangar I could pull the top off the
  CAS next time I go out there.

  Paul Lamar


  John,

  From the top they look the same.  That doesn't make sense though as the
 20B
  fires every 120* of crank rotation.  So, maybe they use different
 gearsets.
  On second thought, that is likely how Mazda manages to use the same
  2-pointed rotor for both the 2 and 3 rotor engines... they use a different
  gear ratio for the 20B CAS.

  I recently tried to adapt a Renesis front cover to my 20B and found that
  the
  injection pump gear wouldn't mate with the 20B crank gear.  I didn't give
  it
  much thought at the time as I wasn't planning on using the oil injection
  pump anyway, so I removed the the oil injection drive gear.  But thinking
  about it in light of the CAS, it makes perfect sense.

  Mark S. - Austin

  The reason it is 2 points is it rotates at half e-shaft speed. All it need
  do
  is identify TDC on rotor one once per revolution of the e-shaft. Hence 2
  points
  180 degrees apart.

  The rest of the timing is done in software with the aid of the lower
  trigger
  wheel as that tells the computer how fast the engine is rotating and the
  computer
  uses that info to calculate when to fire the plugs.  One can have one,
 two,
  three or four rotors. Matters not.

  I don't know why the gear does not fit.

  Paul Lamar

 Paul,

 Ok, that makes more sense.  While we're on the topic of crank angle
 sensors,
 I thought I would tell you about how I rigged up a low-budget ignition
 system in order to run my 3-rotor without using Tracy's EC-2.

 First I modified the CAS to accept three pickups, each located 120* apart.
 (This was the most difficult part of the project.)  Then I used three late
 70's vintage GM ignition modules, each triggered by one of the three pickup
 coils in the CAS.  The coils were wired to three dual post coils, the type
 I
 used were for a Buick V-6.  The two leads from each coil were run to both
 the leading and trailing plugs on each rotor.  For fuel, I used a 4-barrel
 Holley adapted to the stock 20B intake.  It worked amazingly well.  The 3
 ignition modules and three coils cost less than $100.  I'm not sure how
 well
 these coils would work at firing two plugs as they were designed for a
 wasted spark system.  Anyway, it worked for my test rig and was dirt
 simple.  I sometimes wish that I had something similar as a backup for the
 EC-2.

 Mark S. - Austin

 Way to go Mark. Excellent work. Got any pictures of the carb
 set up and ignition sys?

 Paul Lamar

Paul,
I'll see what I can come up with.  Its been a while.

Mark

George Graham ran his engine for years on a carb. Somebody else
has it now. I saw it about a year ago in San Diego. It had a
very crude side port intake manifold. It was not a Holley
and had no means of leaning as far as I can tell.


Paul Lamar