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How to tune in A/F value’s

Fine tuning Air fuel Value's for Gasoline Engines

Contributed By: Enginebasics.com

This section will need to be discussed in two parts. One for N/A vehicles and one for boosted vehicles. The reason being that both like a different amount of fuel to air ratios for the engine to run properly, make good power, and be reliable.

For N/A Applications

- For cruise and idle situations a value of 14.7-15.0 (stoic) will be ideal. This will allow the vehicle to be emissions friendly and fuel-efficient.

- When tuning for max power, an a/f ratio of 12.6-12.8 should be used. Note, this value will be slightly different for each application. Certain motors like to run slightly leaner, while others like a richer mixture to make power. Without the use of a dynamiter (dyno) finding this ideal value will be hard. But the value of 12.6-12.8 will give you a great place to start.

- I have known some tuners to tune highway cruising values to as high as 15.5 A/F value’s for good gas mileage. While I believe this is fine for most cars, it can be detrimental to others, and can cause overheating or warping of certain engine components because of the increased combustion temperatures.

For Boosted or Nitrous Applications

- For cruise and idle situations a value of 14.7-15.0 (stoic) will be ideal. This will allow the vehicle to be emissions friendly and fuel-efficient.

- When tuning for max power, an a/f ratio of 11.5-11.8 should be used. Note, this value will be slightly different for each application. Certain motors like to run slightly leaner, while others like a richer mixture to make power. Without the use of a dynamiter (dyno) finding this ideal value will be hard. But the value of 11.5-11.8 will give you a great place to start. Don’t hesitate to richen that value up even more to a low 11.0 A/F value to help suppress any small amounts of knock that are occurring. While a richer mixture can help detour small amounts of knock, for cases of large amounts of knock, ignition-timing adjustments are going to be more appropriate.

- I have known some tuners to tune highway cruising values to as high as 15.5 A/F value’s for good gas mileage. While I believe this is fine for most cars, it can be detrimental to others, and can cause overheating or warping of certain engine components because of the increased combustion temperatures.

The most important thing to tuning A/F levels is the gauge. Remember to choose a reliable gauge since most of your tuning will rely on this. The gauge should also be installed with great care. Since these gauges are very sensitive to electronic interference, be sure to find a good clean 12v source and ground. Most aftermarket A/F gauges suggest using the ecu ground so that the ECU and the gauges are reading the same ground, and electrical interference will be minimalized.

Another thing to note is that these sensors will become less accurate with time and use. It should be considered a common wear and replace item like tires, oil, and filters.

Do not attempt this without a wideband O2 sensor, and narrow band O2 sensor will not provide you the readings your looking for. Start by purchasing a solid UEGO wideband sensor and gauge: