How to Tune an Apexi SAFC

by Alexander Eliot

Installing an Apexi SAFC device on your vehicle can substantially increase the horsepower potential of your engine. By editing the ECU's stock fuel curves via the oxygen sensor signal, the Apexi SAFC can fine-tune a stock engine to make more power. However, the SAFC's main benefit is with modified vehicles. By custom tuning your SAFC with the specific modifications you've installed, your engine can more efficiently take advantage of performance upgrades. This allows for higher horsepower numbers, as well as smoother, more reliable engine operation. Though professional dyno tuning is always ideal for best results, the Apexi SAFC's tuning interface allows virtually any user to take advantage of its performance potential.

Hook up a data-logger device to your vehicle via an ECU cable. There are numerous data-logging programs that run on various platforms, from laptops to hand-held electronic devices. You can plug your electronic device into the ECU via an ECU cable adapter. (Generally, the ECU port is located in the driver's side footwell.) Then, load the program while the vehicle is in operation to log ECU parameters. Alternatively, an air/fuel gauge can be installed to tune via your engine's air/fuel ratio display. The latter method is generally less precise and effective.

Find a safe, legal place to run your vehicle to redline in second or third gear, such as a highway entrance ramp. Have a passenger operate the data-logger program while the engine is under acceleration. Alternatively, have a passenger observe the air/fuel ratio gauge, noting its fluctuations. Write down the data-logger's or air/fuel ratio gauge's air/fuel mixture readouts at increments of 100 RPM.

Select the "throttle settings" mode on your Apexi SAFC device. Select the "Hi throttle" setting. This setting adjusts your engine's fuel tuning under full throttle. Use the SAFC's controls to navigate its fuel tuning menu. You can navigate left and right to view RPM increments. Increase or decrease the fuel values at these increments to edit the ECU's stock fuel curves.

Use your data-logger or air/fuel ratio gauge notes to determine SAFC tuning. The stoichiometric air/fuel mixture for internal combustion engines is 14.7 to 1. However, to retain engine consistency and reliability, a rich air/fuel mixture should always be used. Refer to vehicle-specific tuning guides to find out the ideal air/fuel ratio for your vehicle. Add or decrease the SAFC fuel values to achieve this ideal air/fuel mixture at all RPMs. You'll likely have to do multiple data-logging and tuning sessions to achieve a good overall tune for your engine.

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About the Author

Alexander Eliot has been a professional writer since 2006. He holds a B.A. in English literature from the University of Cincinnati. His academic background allows him to write articles in all fields of education, as well as science and philosophy. Eliot once worked for a performance auto center, an experience he draws from to write informative articles in automotive theory, maintenance and customization.