XJS & XJ from KWE Cars
Classic Spirit Reborn

KWE Digital Engine Management (DEM)

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.

DEM - what is it?

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 idel 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) 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.

DEM - why have it?

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Technical Note:

  • For a petrol engine to work properly it must receive the right mixture of fuel and air at the right time in the engine’s cycle for each cylinder, and it must receive a spark in each cylinder also at the right time to ignite the fuel which explodes and pushes down the piston in each cylinder, all of which are connected to their own crank (which is effectively a lever) which rotates the crankshaft and ultimately drives the wheels round.
  • These explosions vary in intensity according to how much fuel/air mixture is received by each cylinder – and just as importantly the point at which in the pistons’ travels up and down each cylinder the explosion occurs. Too late and power is wasted, too soon and the explosion damages the poor old piston as it’s coming up the bore. This is known as pre-ignition and produces a characteristic high pitched note called pinking (or pinging in American)!

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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.

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.

4:52 pm KWE Cars