The Garage

Endurance racing

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Homemade electronic ignition


This was created because the root cause of the last engine destroying a piston (see left) was the ignition timing (more precisely, the difficulty of changing advance curves etc.) So, I decided to try to create a simple, more accurate arrangement that could be adjusted somehow.

After a lot of searching for something that did not cost the earth and was not vastly overspecified (i.e. race spec) for my needs, I found a programmable electronic ignition kit sold in Australia. Luckily, the Web solved my problem there...the kit cost about 30, and was originally designed to work still using points, and with an 'add on' actual ignition system (such as a CDI) rather than driving a coil directly - however, it gave a simple programmable advance curve plus a few other features (rev limit etc.). This kit formed the basis of my design, if you could give it such a grand name...

Once I got the kit and detailed info, I could investigate further and found that it should be quite easy to design a bolt-on rotor which, via a Hall Effect device, would trigger it. I therefore designed a rotor which bolts on to the Essex crankshaft pulley, and used an automotive sensor (see picture) The rotor has 3 cut-outs and triggers 3 times each revolution. I designed it with cut outs rather than teeth as this is easier to machine. It did mean that the pulse from the sensor had to be inverted via an extra transistor though…

This rotor does the basic timing straight from the crank, and thus the distributor is only there to distribute the spark, nothing else. However it's internals can usefully all be left in situ in case of failure...

The "other end" of the design was a suitable ignition coil driver setup. I simply bought a transistor capable of this kind of job (nowadays such devices exist) and added a simple driver circuit (2 transistors) to make sure it was switched properly. It needed no special protection to drive an ignition coil, as it's designed for the job!

This collection of bits was then built into a die cast box, incorporating access to the keyboard of the processor etc. There are only 4 input/output wires needed (+12v, 0v, trigger in, coil out)

The main adjustable parameters of the kit part are;

 advance start RPM (300 - 9999 rpm)

 advance intermediate RPM point (300 - 9999 rpm)

 advance intermediate degrees (0 - 45)

 max advance RPM (rev limit also, max 9999 rpm)

 max advance degrees (0 - 45)

 dwell (degrees)

 vacuum advance degrees (if a value for this is used, it is on/off)

 2 switchable sets of above settings (whilst running)


You can see from the above that the kit gives a simple two-stage advance curve, just like a distributor, but it is programmable to give many more variations (even negative advance). All the values are stored in flash ram. Below is a simple drawing of the add-on parts I have built, to interface the kit.



  What happens to your pistons when there's too much advance!


  The kit, boxed and with keypad to swap settings. I put it in the glovebox.


  Bolt-on crank trigger and sensor, yes it adds weight but... :)


  Circuit for driver for the ignition coil.