As mentioned in Pt.1, the Programmable Ignition System can either be used as a complete ignition system or as an interceptor.

Whether it behaves as an interceptor or not depends on the input signal that’s applied to the unit. In most cars, the ignition system will already provide ignition advance with respect to RPM and engine load. This applies not only to cars that have full or partial engine management but also to older cars that simply have mechanical RPM and vacuum advance systems.

When used as an interceptor, the Programmable Ignition simply modifies the existing ignition timing. By contrast, when it’s used as a complete ignition system, we dispense with any existing timing system that may exist and re-map the timing using the Programmable Ignition Timing Module.

If you intend using the unit as an interceptor, then there’s no real need to know what the engine’s existing timing map is for RPM and engine load. That’s because we are simply using the unit to modify the existing timing values at various engine RPM and load sites.

Why would you want to do this? Well, you may want to advance the timing at some sites to gain power and/or retard the timing to prevent detonation (ping) at certain trouble spots within the RPM and engine load map.

Note that although the original timing curve does not have to be known for interception, you do need to know the RPM and engine load range. This is necessary to ensure that the full mapping range is utilised with the Programmable Ignition System (more on this later).

Conversely, if the unit is used as a replacement ignition, it will be easier to program in a timing map if the original engine timing is known. That way, the Programmable Ignition can initially duplicate the original timing which can then be adjusted as necessary in a similar manner to an interceptor – eg, to extract better performance and/or to prevent detonation.

In some cases, full timing information will be available from the car’s manufacturer or from a workshop manual. Usually, however, there will be no information available.

The solution is to actually measure the timing advance against changes in RPM and engine load. This is easy to do in cars with a mechanical vacuum advance mechanism, as this operates independently of engine RPM.

Plotting the timing values in cars that use engine mapping and a MAP sensor for vacuum measurement is only slightly more difficult. It’s done by externally altering the pressure sent to the MAP sensor or actuator. The exact procedure is described in the panel headed "Plotting The Original Ignition Timing Values".

Cars that utilise Mass Air Flow (MAF) sensing of engine load are much more difficult when it comes to mapping ignition advance. That’s because the engine will have to be run with varying degrees of load throughout the RPM range and this can only be achieved on a dynamometer.

Interceptor or replacement?

Note that the Programmable Ignition System should be used only as an interceptor on cars that already have an engine management system. That’s because the manufacturer’s timing map will have been carefully designed for your engine. Furthermore, the timing would have been mapped against air inlet temperature, engine temperature and the air-fuel ratio to provide the best performance in all conditions.

By using the Programmable Ignition System only as an interceptor in such cars, the original timing variations according to fuel ratio, temperature, RPM and load will be retained.

By contrast, we do advocate using the Programmable Ignition System as a complete replacement in older cars and Go-carts and on engines that do not currently include RPM or vacuum advance.

Many old cars provide both RPM and vacuum advance by mechanical means. Because of their age, the RPM advance system is now likely to be worn and sticky in its operation, while the vacuum actuator will often be leaky or may have failed altogether. Most drivers do not notice if a vacuum actuator has failed because when it fails, it remains at the maximum engine load position. As a result, power under load is retained.

Our experience

During our tests, we eliminated the original mechanical RPM and vacuum advance systems in a 1988 Ford Telstar and used the Programmable Ignition System to provide the timing advance instead. As a result, the engine became far more responsive to throttle changes and was more willing to rev than before.

There are a couple of reasons for this improved performance. First, the flying weight system in the distributor that provides RPM advance is fairly sluggish to respond to RPM changes. By contrast, the Programmable Ignition System provides "instantaneous" changes to the timing map.

Similarly, the vacuum actuator that moves the distributor’s trigger firing point is slow to respond compared to using a pressure (or MAP) sensor with the Programmable Ignition System.

Installation

Typically, the Ignition Timing Module is best mounted inside the cabin of the car; eg, somewhere under the dashboard. This allows the Hand Controller to be easily attached and used while someone else does the driving (this should be done on a racetrack or some other closed road).

An external MAP sensor can be mounted on the firewall. It will require power connections plus a vacuum hose connection to the inlet manifold.

It is also best to mount the Ignition Timing Module in the cabin if the Sensym pressure sensor is used. This helps keep the sensor cool.

Alternatively, the Ignition Timing Module can be mounted in the engine bay if you cannot find room for it in the cabin. Make sure it is well away from the exhaust manifold though, to prevent excessive heat exposure. It can be mounted using suitable brackets to the chassis.

The big disadvantage of mounting the unit in the engine bay is that it is much harder to connect the Hand Controller for driving. In some cases, it may be possible to feed the connecting lead through a window and under the rear of the (closed) bonnet. Alternatively, it may be possible to temporarily feed the connecting lead through the firewall (not so easy) or through an air vent (easier).