On 22/11/2016 03:41, RayL12 wrote:

The 9 head rotary engine has a firing stroke that has a directional
change every 80 deg, albeit, 40 degs per 720 deg of engine rotation.

Eh?

AIUI the spark hits every other cylinder as they hit TDC. Two turns and
they've all had one. The non-sparking one is a the end of exhaust /
beginning of induction.

Andy