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.

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.

Paul Lamar


Thanks Paul, any info is much appreciated.

John Bell.