The perfect ratio of fuel to air is 14.7 parts air to 1 part fuel. That’s the ratio of fuel to air that results in the most efficient burn possible, where all of the oxygen and fuel will be consumed. The science of measuring reactions, like the chemical reaction that turns oxygen and fuel into CO 2 and heat, powering your engine, is called stoichiometry. //

Just note, though, that in the real world, your car will be happier with around 13:1. We don’t live in perfect atmospheric conditions, so a little bit of extra fuel doesn’t hurt and will still be considered stoichiometric. //

Of the two, having a lean mixture is much more dangerous for your engine. An engine can run rich without much issue. An engine running lean can become lubricant starved and seize.