Street tuning your car allows you to customize the engine's fuel curves. On stock engines, a more performance-oriented tune can be programmed, increasing the engine's horsepower output. If you've installed other performance modifications on your car, such as intake and exhaust upgrades, street tuning can be even more beneficial. Since performance modifications alter the airflow patterns of the engine, custom street tuning your engine to your particular modification setup allows for optimum engine performance.
Have a piggyback ECU tuner installed on your vehicle. These are electronic devices that tap into the engine computer, allowing user modification of the stock fuel curves. A tuner that allows for air/fuel signal monitoring is preferable, as the engine's air/fuel ratios will be used for tuning purposes. If your piggyback ECU tuner lacks an air/fuel readout, an air/fuel ratio gauge can be installed instead.
Drive your vehicle to redline at full throttle, allowing for the engine to run at its maximum level of performance. Have a passenger note the air/fuel ratios given by your piggyback ECU tuner or air/fuel ratio gauge readout while the engine is under acceleration. Compare these numbers with the ideal engine air/fuel ratio values given by your piggyback tuner's user manual.
Use your piggyback ECU tuner to increase or decrease fuel correction values at any given engine RPM. At RPM values where you noted the air/fuel ratio to be lean, increase the piggyback tuner's fuel correction value. This increases the fuel injection into the cylinder at that particular RPM, optimizing the engine's air/fuel ratio. Alternatively, decrease the tuner's fuel correction value at RPM values you noted as having a rich air/fuel ratio.
Repeat Steps 2 and 3 multiple times to achieve the perfect custom street tune. The more tuning sessions you run, the more optimal you'll be able to set the engine's fuel curves to maximize its horsepower and efficiency.
