Now that the air-cooled Volkswagen Beetle and its siblings rest in peace, only Porsche and Subaru stand by the boxer-engine principle. In a worldwide first, the Japanese have now taught the horizontally opposed piston engine to feed on diesel fuel. The layout? A 2.0-liter, aluminum-block, four-cam four-cylinder.

We tried the promising fuel miser in the Legacy sedan and the Outback wagon, and we came away impressed. Like all horizontally opposed engines, Subaru's new diesel eliminates second-order shaking forces. The end result is a smoothness - and a lack of noise - not usually associated with an oil burner. The 148-hp four-cylinder revs to a 4400-rpm redline, and although it's not ridiculously quick (60 mph arrives in 8.5 seconds, according to Subaru), prompt accelerator-pedal response and a wide, middle-of-the-tach sweet spot go a long way. Fuel economy is expected to average about 40 mpg in Legacy-based applications, and top speed will likely approach 130 mph.

Subaru's diesel hits Europe this month, but happily, its stateside arrival isn't far off - American Subaru dealers are due to see it in 2010. Subaru of America has not yet decided which vehicles it will offer with the diesel, but the Legacy, the Outback, and the Forester seem like obvious candidates. As one would expect, the usual modern diesel equipment will be present, including common-rail, high-pressure fuel injection; four valves per cylinder; a particulate filter; and a variable-vane turbocharger.

If 148 hp doesn't seem like much, fear not: an output bump is reportedly in the works, along with a six-cylinder variant sporting up to 300 hp for certain markets. Incidentally, Subaru is also working on combustion tweaks and a more sophisticated catalyst that will allow its diesels to meet emissions regulations without using urea injection. The mood in-house is nothing if not ambitious. "We think we're on the right track," states a senior Subaru engineer. "In a few years, 30 percent of all Subarus will be diesel-powered." That's a hefty goal, especially since it remains to be seen if diesel cars will really catch on in America. For now, however, Subaru has made a commendable first step.