The normally aspirated petrol engine, whilst not being the easiest of engines to tune, can still benefit from a 8-15% power increase with added torque by careful reprogramming of various engine parameters within the map. Parameters such as the fuel and ignition curves can be fine-tuned to give better power & torque output. On some engines the camshaft timing can also be tuned within the map, giving additional improvements.
In many cases, 'after market' tuning items such as free flowing exhausts, high flow air filters and re-profiled camshafts can only be fully utilised by the engine once the necessary adjustments have been made within the ECU. Careful recalibration of the correct maps can unlock the potential of your new engine parts. Further power gains may also be available when a higher octane fuel is used, allowing for more ignition timing.