As some of you know I am working on a Speedster using Mark Chaffin's RAJO overhead valve kit. The cylinder head has holes for two spark plugs/cylinder. The question of how to fire two plugs/cylinder is addressed here. This is somewhat like Les Shubert's post on this topic but a bit more explicit with how to make the adapters to put the Datsun mid-1980's twin-fire cap and rotor on the Bosch distributor.
I have borrowed the ideas from Clark Callis of Ohio who makes a kit or completed product for doing this. But I thought some of you might like to do this yourselves.
If you are a little bit handy, and/or have access to a good machine shop this is not too difficult.
Since one picture is worth 1000 words, I will post lots of pictures and not too many words.
First, here is the Datsun 200SX mid-'80's cap:
Notice that the cap has TWO coil connections and EIGHT sparkplug connections.
The little brass fitting is to fit the Datsun rotor onto the Bosch distributor shaft.
We are using a hybrid twin ignition distributor on our Gemsa powered racer. It uses the Nissan Z cap and rotor adapted to a Bosch VW distributor with dual electronic pickups. We got it from a guy who builds twin ignition high performance VW engines. Used a Chaffin shaft extension and dropped it right in to the Bosch plate. The Z distributor is designed to turn counterclockwise but the cap and rotor don't' seem to mind turning the other way. The whole thing works well. Take care to ensure the points or electronic pickup are synchronized so that the intake plugs are fired by the intake coil and exhaust plugs by that coil. We did not use spark advance linkage as the unit has centrifugal advance built it. Hope you are as pleased with yours as we are with this one.
This picture shows the adapter plate on the Bosch distributor:
Notice that it is held in place with two small Allen-head set screws.
Here is a top-view plus the little distributor. shaft adapter for putting the Datsun rotor on the Bosch shaft.
Notice the TWO Pertronix "Ignitor" electronic modules in the distributor
Note that the Pertronix magnetic ring around the shaft has FOUR magnets in the ring at 90 degree in increments. So the distributor fires every 90 degrees (one pair of plugs each time).
Looks like you are doing pretty much the same thing!
Here is a close-up of the Datsun rotor:
Note that the contacts (one on the inside, one on the outside) for the two plug wires are at 135 degrees from one another.
The Datsun cap has hook-up identification by each sparkplug connection such as I1, E1 (at 135 degrees from each other). The notation I1, E1 refers to intake side #1 and exhaust side #1,...etc..
Jon, nice work! It looks just like mine. You can expect great performance out of it.
Right now we are trying to get out of town for the FAST races in Santa Margarita. Having problems getting my C4 auto to upshift into high. I'll have to drill my intake for a modulator tap.
Keep up the good work and wish us luck.
Finally, here is an absolutely amazing thing!
One would of course think that the Datsun sparkplug notation on the Datsun cap would be wrong for a Model T. (The firing order for the Datsun is: 1-3-4-2, and, of course, it is different for the Model T: 1-2-4-3.
But the Datsun rotor goes counterclockwise, while the Model T Bosch goes clockwise.
What that means is that one can use the Datsun sparkplug identification stamped in the Datsun
cap for the Model T!
Sometimes good things happen...!