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Air/Fuel Ratio Explained

The Air/Fuel ratio, or A/F, is simply the mass ratio of air to fuel as it enters an engine on its intake stroke. An engines A/F will have a direct affect on engine performance.

There are three basic things that your engine must have to work properly. They are fuel, air, and spark. The goal is to have the air and fuel mixed to a point where every last bit of both the air and fuel are usedin the combustion cycle. When we achieve this "total burn" we are in a stoichiometric state. "Stoichiometry" is a term that means that the most complete combustion is achieved.

All fuels have different stoichiometry. The stoichiometric ratio for gasoline is 1:14.7, or 1 part oxygen and 14.7 parts fuel.

So it's that easy huh? Tune it to 14.7 for the best power right?

No. I wish it was that simple. The 14.7 rule only works for idle, and cruising speeds. Under full throttle load, you would want a "richer" air to fuel ratio. The word "richer" refers to adding more fuel. This is necessary to prevent detonation within the engine.

Every motor is different. Heat, and cold affects air/fuel ratio while driving, and it is constantly adjusted to counter for outside forces affecting on it. The optimum air/fuel ratio for one persons engine could vary greatly from someone elses. It is best to find your vehicles optimum air/fuel ratio on dyno using a wideband oxygen sensor.

Any deeper into Air/Fuel ratio and we'll be starting to tune, so that's a wrap.