The modern catalytic converter (cat for short) can remove most of the hydrocarbons and NOx remaining in the exhaust stream. “Stoichiometry,” the ‘ideal mixture’ of fuel and air, sometimes described as 14.7 pounds of air to one pound of fuel, is the narrow range of mixtures across which the catalytic converter can reduce or oxidize the toxins to acceptable levels. The 14.7-to-1 ratio is misleading, though-just imagine what oxygenated fuel or altitude does to the equation. It’s not quite vitamin-injection into the tailpipe, but it’s a kissin’ cousin.