Been looking at some photos of old 10a and early 12a engines. These engines had dual distributors. Can someone tell me why they did this? Also, I'm curious how the distributors were arranged; i.e., did one distributor feed the front rotor, and the other feed the rear rotor? Or was one dizzy for the leading plugs and the other for the trailing plugs? Or??

Just curious...
-Bug

 

I'm going to take a shot in the dark, but one for leading and one for trailing perhaps?

 

I'll guess that they used 2 distributors until they worked out how to deal with multiple sets of ignition points and cams (mine had 3 sets of points using 2 cams). With 2 distributors a more traditional distributor cap worked. With the 2 distributors the timing and dwell angle could be set independently for leading and trailing plugs.

They also lead to more head scratching when non-rotary heads look under the hood!

 

It's definitely leading and trailing...

However the way the rotary is designed, they only needed a single one. Leading works waste spark...

Take a look at a 1st gen RX-7 distributor rotor and cap versus any other vehicle... Way more complex to try and fit leading and trailing into a single cap.

Dare I say the trailing is more efficient in the dual distributor design. It won't have to just two spark gaps in the distributor, just one.

On the first gens, when we convert to direct fire leading, we move the trailing over to leading so that it goes through the carbon button in the leading side rather than the dual gap setup of the trailing... Hotter spark on the trailing.. Not that that matters much.

 

Well said, Pele.