Air Fuel Ratio: It Matters
To start we should understand that there is an ideal mix of gasoline and air that is desirable for the most complete combustion. This ideal mixture is referred to as the stoichiometric ratio and for typical gasoline engines it is calculated at 14.67 or rounded to 14.7 parts of air to 1 part of fuel as measure by weight. This ratio provides the most efficient combustion with the least pollutants. An air fuel ratio above 14.7 is considered as a lean mixture while any AFR below that is considered a rich mixture. Now with that said the stoichiometric mix of air/fuel has changed some over the years partly due to the addition of ethanol into the fuel and partly due to additives that are added to the fuel. This puts the ideal AFR closer to 15.2 parts of air to 1 part of fuel. That’s right, the engine can actually use less fuel at idle and light throttle cruise than it used to, due to these additions in the pump gas we typically see here in the states.
ARD tuner Robert “Lucky” Arnold tells us why 14.7 is the 3.14 of car tuning.