If your car has a reluctor distributor (it has a star-shaped wheel that generates the timing pulses, usually mounted right under the rotor button), you can upgrade the ignition system in a cheap and straightforward way.
This is the perfect upgrade for older Japanese cars.
This upgrade will work with either type of Variable Reluctance distributor pickups shown here. Note: Hall Effect systems are not suitable for this particular modification.
However, before you race out and start chopping into your pride and joy, read the whole article and have a careful look at your existing ignition system to ensure it’s as described.
What you need
This modification is built around the Bosch 9222 067 021 (or 9222 067 024) ignition module and a matched coil. Both parts can be bought new or second-hand.
Here in Australia that ignition module was fitted to many cars and so is available from wreckers very cheaply. (See end of article for a list of suitable cars.)
Go to a self-serve wrecker, locate a suitable donor vehicle, and on the distributor base will be a cast flange with a sheet metal cover, under which will be a Bosch module - the last three digits should be 021 (or 024). It will have four terminals.
Disconnect the module, unscrew it and try not to wipe the white heatsink paste off the module base - it helps with heat conduction to the heatsink.
You will also need the ignition coil, as well as the mounting bracket and HT lead just to be safe. You can use the donor car’s oil-filled unit (the cylinder type) but if you want a more modern looking transformer coil then you need a Bosch HEC715 (female HT) or a HEC716 (male HT).
If you want to purchase new components see below for Bosch part numbers.
Making the modifications
Using a timing light, establish the standard timing at idle. In order to do this, you may need to refer to the manufacturer’s specifications to establish exactly under what conditions the timing is determined.
Before you remove the distributor from your car, mark the position of the rotor to the distributor body and the distributor body relative to the engine. This makes it easy to reinstall.
There will be a pickup in the distributor body that is on the same plane as the reluctor (the star-shaped wheel that rotates). Two wires will go from the pick-up to the ignition module.
If the ignition module is internal to the distributor, you need to cut these wires and extend them with shielded cable (like audio cable - two cores and a woven metal screen around them) to reach wherever you’re going to mount the new module. The screen must to be grounded at one end only.
If you’re going to remove the pickup to make the installation easier, first measure the gap between the reluctor and the pickup coil. Sheets of paper / plastic etc will work fine although brass feeler gauges are the correct tool.
Make certain you insulate the wiring joins well (use heatshrink) and ensure the new extended lead is clear of the rotating components of the distributor.
When selecting shielded cable, try to use a good quality silicone insulated product. It’s hot and unfriendly under the bonnet, so a quality cable is a good investment. Keep it away from all the hot engine bits and thermally shield it if necessary - fiberglass sleeving is ideal.
If the ignition module is already externally mounted, you may well be able to use the existing trigger wiring. Check to see that the cable shield is grounded at one end only - it is important.
The old module can be removed or left – it’s your choice. If you remove the old internal module, the new shielded cable may be able to exit through the existing cable grommet, making for a neat installation.
If you removed the pickup from the distributor when cutting and extending the wires, put it back and set the gap between the reluctor and pickup coil to the same gap as previously.
Put the distributor back using the alignment marks you previously made.
Mount the coil and module. A small heatsink is required for the module, so make a 3mm thick aluminium bracket about 70 x 50mm for the module. Do not run the system without a suitable heatsink.
If you wiped of the heatsink paste during removal of the module, electronic component suppliers usually sell it. It is important to make good thermal contact between the module and its new heatsink.
The connections on the module are:
Ignition power goes to the coil positive terminal and to module terminal 15. A ballast resistor is not required. In fact, a ballast wire or resistor will undo all your good work! You can pick up power from the old coil positive connection on the loom (not the old coil - just its loom connection).
Coil negative goes to module terminal 16. Connect the new coil’s negative to the old coil’s negative terminal on the loom, so the ECU / tacho gets ignition pulses.
The shielded cable that you have just installed goes to terminals 3 & 7 – but don't make them permanent just yet. Make sure the screen is grounded at one end as described previously.
The module shell is connected to the vehicle ground via its bolted connection to the heatsink. Make certain both the module and the heatsink have a good electrical ground connection. “Star” or serrated washers may be used to assist in this.
Time to start the engine
That's it... time to start the monster.
Get a timing light - if you have to substantially rotate the distributor body to get the timing right, then reverse the connections to terminals 3 & 7 and recheck.
This matters because a reverse connection might run the engine, but the dwell control in the module will operate incorrectly and the rotor may no longer align with the internal posts / lead connections moulded into the distributor cap,
If you have an oscilloscope, you can verify the polarity manually. With the distributor removed (remember to mark alignment as before) - rotate the distributor drive in the normal direction of rotation and observe the pickup coil’s output waveform. As the pole passes the coil’s projecting tooth, the waveform should swing positive first then go negative. You have now identified the trigger coil’s “+” and “-” wires, so connection to the module is straightforward.
Connecting a standard oscilloscope to the coil or module while the vehicle is running is not recommended.
You now have a high performance, variable reluctance triggered, inductive ignition system, powerful enough for most boosted installations let alone a stock vehicle - more than a match for OE or aftermarket systems.
Total cost second hand depends on the wrecker, but $20 is about it. New parts will obviously cost more.