Original submission by T Nov 25th 2006:
The Bosch made L34 Distributor had 2 Coils feeding into the same Distributor Cap. Each Coil sparked alternate Cylinders minimising the frequency of sparks required from each coil and increasing the available spark at high RPM. The US made DuCoil worked similarly but differed in that it located a circular track under the Distributor Cap and placed a second Carbon Brush on the Rotor Button itself.
Each of the 2 Coils were triggered by its own set of Breaker Points and Capacitor.
A special Rotor Button with 2 Arms directed Spark Energy from each Coil to the matching location on the Distributor Cap. Submission by John (Arsewipe): There are only 4 lobes on the cam instead of 8, as each coil only needs to fire 4 times each revolution. This ensured that the primary field remained closed for longer duration.
The points would have to be at a position other than 180 deg. apart (typically 135 deg), as if they were opposing each other then the cylinders would fire similtaneously. This set up significantly lessened the likelyhood of point bounce. End of submission by John (Arsewipe):
One Coil Output Lead connected into the centre of the Distributor Cap just like in a normal Distributor. This connection also connected to the Rotor Button Arm just as it does in a normal Distributor. The second Coil Output Lead connected into a location on the side and top of the Distributor Cap. Through a Carbon Brush the Spark Energy was directed to a circular track located on the Rotor Button. From there the Spark Energy was directed to a second Arm on the Rotor Button, positioned 180 degrees away from the normal Arm. You can see the brass Circular Track on the Rotor Button in the image as well as the normal and secondary Arms extending from the Rotor Button. ===Firing Order:===
Since each Coil sparked Alternate Cylinders the location of the Plug Leads in the Distributor Cap had to be relocated compared to the normal Distributor. For a typical Aussie V8 with a firing order of 1, 2, 7, 8, 4, 5, 6, 3, the first Coil will typically fire Cylinders 1, 7, 4, 6 and the second Coil will fire Cylinders 2, 8, 5, 3.
===Distributor Lead Sequence:===
The lead sequence in the cap is 1,5,7,3,4,2,6,8.
The arrangement made for a greater spark at high RPM since each Coil performed work at only half the rate of a single Coil and Distributor combination.
===L34 Dual Coil Distributor Animation:===