Rotary firings

[Andrew Ghali]

On Wed, 16 Sep 1998 23:54:59 -0400, Clare Snyder <clare.snyder.on.ca at ibm.net> wrote:
>
>Bruce Plecan wrote:
>> 
>> Just a tad rusty here, but (on a 2 rotor rotary), aren't the rotors, and
>> shaft geared at 1:1,so at 1K rpm there are 2K exhaust pulsations?...
>>   Where as in a 2 cylinder 4 stroke would only have 500 pulsations
>> per minute at 1K rpm idle?.
>>   EFI content is that this is in reference to O2 sampling.
>> Cheers
>> Bruce
>Nope - usually NOT 1:1 Closer to 3:1 if I remember from back in the R100
>and RX3 days when I worked for a Mazda dealership.

This is a copy of something I posted some time ago, based on my experience
and documentation on hand for both my '87 normally aspirated (that's Mazda
for non-turbo) and my '93 twin turbo.  I hope this helps.

Most Mazda rotaries (i.e. almost all) have 2 rotors (13B or the earlier 12A)
not counting triple rotor Japan-only and racing engines (20B and 20G), or
even the few 4 rotor beasts you won't find on a street.  According to my
documentation, you get one rotation of a rotor per 3 turns of the eccentric
shaft (piston engine fans read: crankshaft) with 3 faces per rotor, which
give you 120 deg between pulses per rotor or 180 deg per turn of the e-shaft.
Due to the long, narrow cumbustion geometry, there are two plugs per rotor -
the leading and trailing plugs.  The trailing plugs are above the leading
plugs; roughly at 2 o'clock while the leading plugs are at 4 o'clock.
Trailing plugs are fired by individual ignition coils (in the 13B-REW of
the 3rd gen twin turbo) or ignitors (earlier 13B), while the leading plugs
are tied to a single coil or ignitor as waste fire.  Timing at idle is fixed
at 5 deg ATDC leading and 20 deg ATDC trailing, while at crank it is fixed
at 5 deg BTDC (both?), and variable everywhere else (on a 13B-REW).

Andrew