Modern cars rely on ECU, or engine control units, to control the ignition, the amount of fuel, the idle speed, valve timing and other essential processes. Effectively, an ECU is a microprocessor that reads data from a number of sensors mounted on the engine and in the exhaust, processes the data, and from the results determines the appropriate outputs to control the various engine management functions.

The data that determines how the ECU should respond to various inputs is pre-programmed in an EPROM (electronically programmable read only memory). This is effectively a multi-dimensional database which is known as an engine map.

Engine maps are developed by car manufacturers using a combination of computer simulations and physical tests. Ultimately, they provide an optimum solution which involves a number of compromises, for instance between the car’s acceleration and its fuel economy. If you change the map (a process known as remapping) then you change the performance of the car.

If you are seeking to improve your car’s performance, then remapping the ECU can produce sometimes startling improvements in performance. It enables you to increase the brake horsepower (bhp), to increase the amount of torque, to modify the throttle response so that the car picks up seed faster, and to even out the power delivery through the revs.

With a non-turbocharged engine, ECU remapping can achieve up to around 15% improvements in both bhp and torque, and the improvements with turbocharged engines can be very much greater. Typically the performance of a turbocharged petrol engine can be enhanced by up to 25% and up to 30% for a turbocharged diesel. In many cases there is also a potential improvement in fuel economy but only if no advantage is taken of the improved performance potential.

On modern cars manufactured after 2000, ECU remapping is carried out entirely by software. There is no need to physically change any chips or circuit boards and many remapping companies will carry it out at your own location. The technician simply plugs a computer into the OBD input in your car and changes the map for a more optimum one.

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