3-SERIOUS; BMW ANSWERS THE CALL FOR FRUGALITY.(NEWS)

Byline: BOB GRITZINGER

JUST HALFWAY THROUGH ITS life cycle, it would be expected if BMW didn't make substantial changes in the 3-series line, especially considering that four years after its introduction, most enthusiasts maintain that the fifth-generation model remains one of the best sports sedans on the planet, if not the best.

With the downward spiral of the global economy threatening to knock the legs out from under the luxury-car market, BMW is responding in a very serious manner with its mid-cycle enhancement of the 3-series. For 2009, there's a light restyling of the sheetmetal, a vastly improved iDrive controller system and the biggest news: the introduction this month of a 50-state-legal diesel in the 2009 335d sedan.

In U.S.-spec trim, including a urea-injection exhaust-treatment system needed to meet federal emissions standards, the 3.0-liter twin-turbodiesel inline-six 335d gives up little to its gasoline-powered 335i sibling. The all-aluminum diesel's 265 hp is outclassed by the 300-hp gasoline version, but torque jumps to 425 lb-ftup 125 lb-ft from the 335i.

With curb weight the same, the diesel runs 0 to 60 mph in six seconds flat, just 0.4 second slower than the gasoline model. Yes, you'll pay about a $1,500 premium for the diesel engine, but you'll drive about 35 percent farther on each gallon of fuel in the 335d, which boasts a combined average of 28 mpg. (Yes, diesel costs more, but government estimates indicate that diesel will cost just 15 percent more than regular unleaded for 2009, so you still save at the pump.) Top speed is limited to 131 mph, but adding the sport package boosts that by 10 mph.

Turbo lag is nonexistent, thanks to a two-stage twin-turbo system that uses a small turbocharger for optimal response at lower rpmthe engine produces 390 lb-ft of torque at as low as 1,500 rpmwhile the larger turbo serves as a precharger for the small turbo at lower speeds and takes more than 95 percent of the boost work at higher engine speeds. The engine also employs the same high-pressure direct-injection system used on BMW gasoline engines.

As a result, the diesel offers serious scoot from a standstill, and it stays strong right up to the 5,500-rpm redline. While we noted some lag in the midrangelooking for highway-speed passing power, for instancemost of the delay was in the standard six-speed automatic transmission's reactions to paddle-shift inputs. When set in D-sport mode, the tranny downshifted smartly on throttle kickdown, providing ample oomph in passing situations. The automatic will be the only gearbox offered with the diesel in the United States.