PWC Workshop: to electronic or not to electronic?

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More and more classic cars have electronic ignition (some pre-wars even electronic petrol injection!). There are great fans and there is strong opposition. So we throw the 'dead cat' on the table and show you the how to and love to gauge your opinion either pro or con...

Altough not original, one can have its reasons why to equip his car with this modern part. Today we would like to give you some explanation of the ignition itself. And in next weeks article, we will explain how to convert your car to the system.

The question is why to use an electronic ignition on your classic or vintage car? There are two main reasons. First: you cannot get the parts or revision of a magneto is too expensive.
Secondly: comfort. I'll explain this last argument later on. I'll first give an overview of the components of an electronic ignition: the electronic sensor, the electronics and eventually the software and the coil.

Electronic sensor
The electronic sensor replaces the breaker points and gives the signal to the electronics to activate the coil and to give a spark. I'm using Hall sensors of Honeywell. I have two types.
The SR17C is a fork model and through the fork runs a (soft iron) vane. For a 4 cylinder engine the vane has 4 blades. When the blade enters the sensor the coil will be activated by the electronics; leaving the sensor the activation stops and there is a spark. The second is a SR13R. This one is activated by magnets. Above the sensor a rotor is turning with 4 x 2 magnets (4 cylinder). When a northpole passes, the coil will be activated. A southpole initiates the spark.
The length of the blades or the distance between southpole and northpole determines the dwell angle. For a standard coil the dwell time is about 4 milliseconds. However, the speed of the engine influences the dwell time. So the length of the vane blades will be chosen based on two third of the top revolutions of the engine.
The use of a (breaker point) capacitor is not neccessary anymore.

Electronics and software
The electronics translates the sensor signal to a switch of the main transistor. The main transistor in the electronics switches the coil. Now there are two types of electronic regulation. First: you can have a fixed ignition timing. The neccessary retard of the ignition will be regulated by hand, or by mechanic and/or vacuum retard.
Secondly: The ignition timing will be regulated fully digital by a processor. The ignition timing is mapped in the software and depending of the revs of the engine the electronics regulates the ignition timing. Also the dwell angle will be regulated by the software, so there is always a fxed dwell time of 4 milliseconds.
For a classic or vintage car I don't advise to buy a fully digital ignition. The price is higher and the advantage is negligible, unless there are non solvable problems with the mechanic or vacuum retard.

Coil
The coil is the most important part of the ignition. The coil transfers low tension to high tension. For a powerfull spark it's neccessary to have the best coil you can get. A coil that's getting warm or hot, you can better throw it away. A temperature of max 40° C is rather normal. Is the temperature higher, the dwell angle is too big or the coil is defective. Always buy a coil of the well known brand e.g. Bosch, BERU, etc. For a 6 volt car a BERU ZS 105 is suitable; for 12 volt choose the BERU ZS 106.

What's the comfort?
• No periodic adjustment of the breaker points• Always correct ignition timing
• Adjusting of ignition with LED light
• No capacitor
• Indifferent for humidity
• Powerfull spark (=fuel efficiency)

What's the disadvantage?
• You have to adapt your distributor to install the sensor and rotor; you have to do some mechanic work
• You car is not original anymore (forget Best of Show at Pebble Beach)

Words: Bert van de Zand
 

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