Horsepower is overrated. There. I said it. Horsepower always seems to be the major selling point, whether you're talking economy cars or super sports cars. Horsepower's basic definition is X amount of work done over a given period of time. So typically even your highest horsepower engines reach peak power late, often very late, in the rev range.

Though many may never realize it, more important to your average driver, and more relevant to everyday driving, street driving, driving beneath triple-digit speeds, is torque. A well-sculpted torque curve means instant gratification when its peak is delivered near instantly in the rev range. And this is definitely the case with our newest long-term test car, this 2009 Space Gray Metallic BMW 335d.

Maximum torque available beneath 2000 rpm--where a really good torque-optimized powerplant will deliver it--gets you off the line in a hurry. Applied abruptly, it chirps tires and snaps necks. Applied abruptly in copious amounts, it turns high-tech, computer-optimized rubber-and-silica compounds into so much boiling tire smoke.

Ah, torque, glorious torque. The wellspring from which all stoplight-to-stoplight bragging rights, quarter-mile pissing contests, and gratuitous displays of "power" flow.

The 335d makes its maximum torque figure of 580 Nm, or 427.7 lb-ft, at just 1750 rpm. That peak hits at less than 1000 rpm off idle. By comparison, the E90/E92 M3 makes its maximum torque of only 295 lb-ft about 2000 rpm later at 3900.

But it's not just about off-the-line hooliganism. It's also about immediate acceleration at just about any speed, given you keep the tach needle somewhere between 1800 and 3500 rpm. So the 335d is a surprisingly good performer even at high speeds. It's electronically limited to 155 mph. We haven't been there yet, but it is willing to run up through triple digits with impressive urgency.

Of course, there are other things to consider. Foremost among them today is fuel economy. For years Europe's solution to improved economy and reduced greenhouse emissions has been clean diesel. This is in stark contrast to Japan's answer, hybrid technology. Hybrid technology is clean and efficient, no doubt. But it's terribly limited in scope. It's at its most efficient in city driving and necessitates adding massive amounts of ballast in the form of heavy lithium-ion batteries, which, if you're even the least bit interested in sporty driving, can completely throw off vehicle handling dynamics.

A diesel-powered drivetrain, on the other hand, shakes out exactly as a gasoline-powered drivetrain would, meaning two similar cars equipped with either configuration would essentially behave dynamically the same on the road. The 335d offers an alternative powertrain without compromising the 3 Series' inherently great driving dynamics.

But I digress--back to fuel economy. The EPA estimates the 335d will average 23 mpg in the city and 36 mpg on the highway, with figures as high as 43 mpg feasible. Averaged over our first 4,000 miles with the car, our 335d has returned combined economy between 26 and 28 mpg. That includes some open highway stints, but mostly street driving and freeway commutes (often in heavy stop-and-go traffic). Pretty impressive. We have yet to tackle a long-distance hyper-mileage run where we'll try and wring the maximum economy figure from this car, but rest assured it's in the works.

In all honesty, I've discovered nothing I don't like about this car aside from the run-flat tires that were supplied with the Sport Pack option. Although they seem reasonably grippy and quiet at speed, run-flats inevitably contribute to an overly jarring ride over bumps or sections of poor pavement. It seems likely we'll swap them for some sort of high-performance summer rubber at some point in the not-so-distant future.

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