Digital Engine Management is a means by which the major functions of an engine can be controlled and modified electronically. KWE have developed a system which is especially relevant to the earlier Jaguar V12 engine, but can be applied to any petrol engine. This article explains what it is, what it does, and how it benefits classic engines.
Central to a DEM system is the central processor unit or ECU (engine control unit). This is an electronics unit containing microprocessors, input and output circuits and programmable memory. Also part of the system are sensors to detect engine revs, timing, temperature, engine load, and throttle position. The unit replaces the existing car’s ignition system up to the distributor, the idle control unit and the fueling control system (usually Lucas on the V12 XJS). Additional sensors need to be fitted to provide the necessary signals for the ECU. The (horrible) original V12 idle speed controller (aka AAV or Extra Air Valve) is replaced entirely with a modern digital speed controller. The system is entirely programmable (otherwise known as mapping) so that exactly the right amount of fuel is injected, and spark timed just right to obtain the maximum power at all loads and speeds. This can only effectively be done on a rolling road dynamometer. The KWE installation uses all new wiring and sensors, and the Omex system we use is widely supported and spare parts are readily available. We have fitted many systems, with great success. Typical power and torque improvements without other modifications to the engine are around 30bhp – more so for early cars, and less so for later cars with their better-developed oem systems.
In the days before electronics, the control of when the spark arrived to ignite the fuel/air (otherwise known as Ignition Timing) was controlled by mechanical means. To make life more complicated the point in the engine’s cycle that a spark is best produced needs to vary with the engine’s speed, and the power being asked of it. In very early cars this was so difficult to achieve that there was a mechanical lever on the steering wheel for the driver to adjust for maximum power and least pinking. The driver’s brain was the best and cheapest computer around!
As the years went by various quite sophisticated mechanical systems were developed to give good control. But with the advent of electronics and the demand for very high efficiencies from engines (and the resultant low carbon emissions) electro-mechanical and eventually fully electronic systems began to arrive – in the 1970s.
At the same time, the method of controlling the amount of fuel delivered to the cylinders was being developed from carburettors which were purely mechanical to electrically operated high pressure fuel injectors which gave designers the ability to meter the fuel extremely accurately and repeatably. As you can imagine, the mechanical systems for fuel control and ignition timing were rather unreliable and crude, leading to a whole industry devoted to maintaining and improving these systems.
The Jaguar V12 engine in common with engines of that era was subject to fairly wide variations in performance coming off the production line due to less than consistent tolerances in the machinery. This meant that the ECU had to be set such that it suited the ‘worst’ possible engine, which in turn meant the the average and ‘best’ engines were not optimally mapped. This problem can now be solved by optimising fuelling and ignition for an individual engine with DEM.
As it can be seen, the process of reliably and accurately controlling the engine’s operation is fairly complex and necessitates modern electronics to do the job well. The KWE system allows full control of the engine and optimises power at all points of the load/speed curve. In addition this reduces fuel consumption and emissions. Idle speed is electronically controlled, unlike the highly unreliable V12 extra air valve. While this installation is not cheap, it provides a future-proof modern system, entirely transparent to the owner. The installation is discreet and the changes are only visible to an expert. We are continually improving our installation procedure and so prices are falling. Our current price (April 2018) is around £5500 + vat – the actual amount varying depending on the model and whether a high pressure fuel system is specified.