ECU remap basically changes the fuel and ignition timing settings from the standard values. ECU is the brains of the car, its what controls how much fuel goes into each cylinder and when the spark is fired. On a N/A car (non boost) a remap wont give much of a gain, (5-10hp or so) but it will smooth out the power delivery and make a car that feels better to drive, it will also improve MPG as the car uses the fuel better. Prices vary from the £30 ebay chips to the £150+ proffesionals charge, ofcourse a proffesional remap will be the best as the chip will be suited to your car, rather than have preset values.
