Manufacturers are preparing for upcoming CAFE changes which will require corporate fleets to average 34.1 mpg by 2016. As a result, a number of auto manufactures are turning to direct injection, turbocharging, hybrid technology, and full electrics to boost their fleet fuel economy.

General Motors is taking a big step, according to GM Inside News, to improve the fuel economy of its bread and butter midsize sedans. The next generation Chevrolet Malibu (due out as a 2012 model) will reportedly only be available with four-cylinder engines.

The current generation Malibu is available with a four-cylinder base engine and an optional six-cylinder engine like most other midsize sedans on the market. It's likely, however, that the next Malibu will use two new four-cylinder engines featuring direct injection technology -- the base engine will be normally aspirated while the uprated motor will be turbocharged.

GM already uses this approach with the new 2011 Buick Regal. The base Regal is available with a 2.4-liter four-cylinder engine producing 182 hp and 172 lb-ft of torque. An optional 2.0-liter turbo four-cylinder engine producing 220 hp and 258 lb-ft of torque will be made available later in the model year. An even more potent Regal GS will come later next year with an uprated turbo four producing 250+ hp.

Another manufacturer that is going four-cylinder-only is Hyundai (along with its accompanying Kia brand). The 2010 Sonata is currently only available with a 2.4-liter four-cylinder engine (24/35 mpg). The 2011 Sonata will be available with a 2.0-liter turbo four cylinder which outpowers and outgrunts the optional V6s in other midsize sedans while delivering 22 mpg in the city and 34 mpg on the highway. Both powertrains will also make their way into the upcoming 2011 Kia Optima.

Toyota's Camry and Honda's Accord are both due for complete redesigns within the next two years, so it would be interesting to see if they too go for a top to bottom four-cylinder engine lineup.