Performance tuning focuses on tuning an engine for motor sport, although many such cars never compete but rather are built for show or leisure driving. In this context, the power output, torque, and responsiveness of the engine are of premium importance, but reliability and fuel economy are also relevant. In races, the engine must be strong enough to withstand the additional stress placed upon it, and so is often far stronger than any mass-produced design on which it may be based, and also that the vehicle must carry sufficient fuel. In particular, the transmission, driveshaft and any other load-bearing powertrain components may need to be modified in order to withstand the load from the increased power. Performance tuning can also include replacement and thus optimisation of transmission components such as the stock stick shift with a short shifter and the OEM shift knob with a Weighted Gear Knob
In addition, changing fuel maps to coincide with the stoichiometric ratio for gasoline combustion may also realize performance increase. Most manufacturers tune for optimum emissions and fuel economy purposes which can limit performance.
Cars with a turbo fitted can have the requested and allowable boost levels raised, these applications usually have the most effect if the turbo fitted is a low pressure turbo which leaves the most room for improvement.
Another reason to change the ECU map is if there are engine, intake, or exhaust modifications to the car. These “bolt-on” modifications alter the way that the engine flows, often causing the air to fuel ratio to change. Without re-mapping the fuel tables, some of the performance gains from the modifications may not be realized.
A poorly tuned ECU can result in decreased performance, driveability, and may even cause engine damage.
The most common way to ‘upgrade’ the ECU is using either plug in modules as mentioned above or using a specialist tuner who will use an OBD Flash tool. These devices generally plug into the diagnostic port although in some cases the reprogramming is done directly on the circuit board. Maps are supplied by tuners.