Now that federal regulators consider diesel engines to be potential fuel savers, we'll likely see the onslaught of clean diesel-equipped cars increase—and that's a good thing. As Autoweek reports, it's only to be expected that Subaru would release the first horizontally-opposed diesel block, given its bias toward boxer engines.

So why a boxer engine? The article reviewed the benefits: a low center of gravity, a lower hoodline, and less potential for unwanted vibrations. Combine that with clean diesel technology, which offers tons of torque, great fuel economy, and low emissions, and you get a pretty good recipe for the perfect drivetrain.

"Though this first-generation diesel boxer is refined, smooth, frugal and driveable, another variant is likely to be the engine sold in the United States," the report said. "The next Legacy gets bigger and heavier, so Subaru concedes that it will need more power. The U.S. diesel also will have to work with an automatic transmission, again demanding more power. And to get through U.S. emissions testing, Subaru must add the latest-technology piezoelectric fuel injectors. Expect the U.S. diesel engine to produce about 175 hp, versus the 148-hp European version. "

While diesel Legacys and Outbacks go on sale in Europe this spring, Subaru plans to launch U.S.-spec versions in 2009.