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