SLK

We rarely think about what's in our gasoline when we fill the tank, but carmakers have to. Mercedes-Benz has just launched a new direct-injected 3.5-liter V-6 engine in its 2012 SLK model, with an innovative "lean burn" mode that will also be used on a smaller four-cylinder engine. The "Stratified" engines are far more efficient under certain conditions than conventional engines, raising their efficiency and the gas-mileage ratings of the cars they're used in. But the company can't bring the most advanced "Stratified" engine to the United States, because U.S. gasoline has far too much sulfur...