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