Factory ECUs are very well tuned and most modern factory ECUs are far more advanced than the most expensive aftermarket ECUs available. Many of these ECUs can be reprogrammed via a chip and tune method where the main EPROM (chip) is removed from the ECU and reprogrammed or a reflash method where reprogramming can be done via the OBDII diagnostics port.
The APET drag GTR still uses the factory ECU that has been tuned to an astonishing world record of 1160hp. This has been done by replacing the factory EPROM with a reprogrammed one that has been tuned to run the far from standard setup.
Factory tuned ECUs however are tuned to allow for any situation including fuel types that aren’t available in New Zealand. They are also tuned to an “over safe” standard. This reduces power output to guarantee they don’t have any problems even when run on the lowest octane rated fuel that may be put in it. Although this system is good for the vehicle manufactures means they are usually well short of their full potential.
Typical gains of a dyno tune for a non-turbo, non-modified vehicle is a 10% power increase as well as a 10% better fuel economy. With a few other simple modifications these gains can be up to 30%. For turbo vehicles gains of up to 40% can be achieved without major modifications.