twin plug distributor firing question
 

Hey guys,
an old porsche book says about twin plug distributor that there is a little time difference between the first and the second plug firing in each cylinder, whereas others, in this forum, say that each pair of plugs in a cylinder fires simultaneously.

Comments?

Thank you in advance for your help

Both upper & lower plugs in each cylinder fire simultaneously.

+1,.............simultaneously. In a simple explanation the twin plug setup allows you to retard ignition timing a bit, yet still retain a good flame front and complete mixture combustion across the cylinder. Gives a good safety margin against detonation, but doesn't cause big drops in torque and engine response liked you'd get in a single plug setup with the same timing retard :)

There is a mechanical advance mechanism in one of the twin plug distributers in my 1990 3.6 engine. I had assumed it was to spread the timing of the 2 ignition points at speed resulting in an effective longer spark duration Or perhaps to allow for drivebelt stretch with speed. Anyone know for sure why its there??

The speed of travel for the spark is constant (or nearly so). As the distributor shaft increases rotational speed, the sparks coming from the coils; which have no inertia lag, will arrive at the middle of the spinning rotors before the rotors align with each of the six spark plug wire conductors molded into each of the distributor caps. The purpose of the weighted assembly is to cause the rotors position to advance slightly in order to maintain synchronization with the spark delivery at higher RPM. This rotor advance mechanism has nothing to do with the ignition "timing" and there should be no lag between the primary and secondary set of plugs firing.

Thanks,
Mark