The final EPA fuel economy numbers are in for the new 2012 F30-chassis BMW 328i, and they’re mighty impressive: 24 mpg city, 36 mpg highway, when equipped with an automatic transmission. The 240-hp 2.0-liter four-cylinder isn’t just a miser, it’s powerful enough to catapult the sport sedan to 60 mph in 5.9 seconds. Not bad for the base 3-series! In fact, that’s a full second faster than the old normally aspirated six-cylinder.
What’s far more interesting, however, is to look at last year’s diesel-powered 335d sedan. It’s a vehicle we adore, powered by a smooth 3.0-liter in-line six diesel that makes slightly more power (265 hp) and a lot more torque (425 lb-ft versus 260) than the new four-cylinder gas N20. But that diesel engine is wrapped in the old E90-chassis body. The E90 might be one of the world’s best sport sedans, but it’s last-generation goods, and that means a last-generation transmission (a six-speed automatic versus the new eight) and last-generation aerodynamics (Cd of 0.30 versus 0.26). And in the case of the 335d, a diesel that’s now two generations old.
So what’s the fuss? The diesel scored 23 mpg city, and 36 mpg highway—giving it a combined rating of 1 mpg less than the new gas engine. Worst part? The factory quotes a 0-60 mph time of 6.0 seconds—one tenth slower than the new 328i.
That means the new F30-chassis 328i is not only more efficient than the old diesel hotrod, it’s faster, too.
This is no slam to the 335d—it was a magnificent car in its time, and it’s still a pleasure to drive. I’d own one in a second—and no doubt BMW buyers agreed: one in ten rear-wheel drive E90 sales wore 335d badges. But it confirms what we thought when we first encountered that car: a big, powerful 3.0-liter is probably overkill for the little 3-series. Then, like now, we think the ultimate silver bullet with a Roundel would be a 323d—a high-performance four-cylinder diesel.
Europe’s “23d” engine is a two-turbo-diesel 2.0-liter that makes 201 hp. Installed in a 3-series with an eight-speed automatic, we estimate that it could hit 60 mph in 7 seconds flat and score (are you sitting?) 34 mpg city and 45 mpg highway.*
Can you imagine the big, metric-sized can of Shut-Up that BMW would serve to the hybrid crowd if the world’s favorite sport sedan could deliver 40 mpg overall and beat a Prius to 60 mph at half-throttle?
We know why the diesel 3-series came here with a huge engine: federalizing an engine costs beaucoup bucks, so BMW could homologate only one diesel for sale in the U.S. The 35d engine could be used in the X5, which needed diesel power (and the resultant fuel economy benefit) the most—and a four-cylinder would have been too small for that application.
The forthcoming ActiveHybrid 3 uses the turbo-six gas engine—that model was conceived and planned at a time where BMW didn’t think fuel economy would be as important as outright performance—so we can imagine that, like the ActiveHybrid 7 and X6 models, will be a monumentally slow seller at best.
However, now that the 335d experiment appears to have been successful, fuel prices seem to have stabilized at “expensive,” and everyone’s in 1980s fuel-crisis mode all over again, we hope BMW can get a four-cylinder diesel here, stat.
* We arrived at these estimates using the F30 328i’s ECE ratings as a baseline, comparing them with the F30 320d’s, and then adjusted the numbers down at the same ratio as the 120d to 123d – then extrapolating those numbers by comparing the ECE 328i versus US 328i and subtracting a mpg or two to get the engines to conform to U.S. emissions standards. For the record, the 320d scores the following on the notoriously optimistic European fuel economy tests: 43.5 mpg city, 60.3 mpg highway.