Carmakers are responding to high oil prices and strict fuel-economy standards by replacing large gasoline engines with smaller, more-efficient ones. And frequently, they are using turbochargers to make the switch without sacrificing power. The problems with turbochargers have typically been high cost, mechanical complexity, and a delay in power delivery called “turbo lag.” Using two turbochargers reduces turbo lag but further increases complexity and cost. Twin-scroll turbochargers solve all of these problems. Long found only in pricey sports cars, twin-scroll turbos, which mimic the effect of a pair of turbochargers, are now appearing in less-exotic cars, such as the 2012 BMW 3-series. The new TwinPower four-cylinder produces just as much power as the six-cylinder it replaces while using 15 percent less fuel. Nearly every other carmaker is working on similar downsized, turbocharged engines. See how the turbocharger works here.