[6] Bmw 328i Twin Turbo Becomes This Month Headline

When BMW introduced the 2009 335d, it was touted as a great blend of performance and fuel economy. In truth, most diesel buyers are more fuel-economy focused, but at the time, BMW was gingerly testing the diesel waters with one engine for the American market. And since that engine had to be powerful enough to motivate the much heavier X5 SUV, BMW selected a 3.0-liter six that was too large to deliver fuel-economy bragging rights in the smaller and lighter 3-series sedan. (Of course, with 475 lb-ft, it did deliver some tire-smoking fun.)

By the end of this summer, BMW will solve this problem by introducing the 328d, powered by a 2.0-liter four-cylinder turbo-diesel developing 180 horsepower and 280 lb-ft of torque. This engine still delivers sufficient performance to accelerate to 60 mph in about seven seconds and will come only with the excellent eight-speed ZF automatic transmission.

A 3-series BMW with VW Jetta TDI Fuel Economy?

BMW says that fuel economy, which is not yet finalized, should improve by at least 20 percent over that of the gas-fueled 328i automatic, which is rated at 22 mpg in the city and 34 on the highway. That calculates to about 28 and 40 mpg, and BMW is suggesting that the highway number might come in as high as 45.

View PhotosMARC URBANO, THE MANUFACTURER

The engine that achieves this economy is the N47 that has been around in Europe for years. It has an aluminum block and head with a single, twin-scroll turbocharger featuring electronically controlled variable exhaust geometry to minimize turbo lag. Peak boost pressure is 22 psi, and the direct-injection system squirts fuel into the cylinders at up to 26,000 psi.

Two Tanks Are Better Than One

Meeting American smog standards in a car the size of the 328d requires the addition of a urea reduction catalyst to control NOx emissions. A tank located near the trunk holds sufficient AdBlue fluid to last between normal oil-change intervals, or somewhere between 6000 and 10,000 miles. Adding fluid is easy because the nozzle is next to the diesel fuel filler under an enlarged flap. That’s a good thing, because the EPA regulations require that the car not start if the AdBlue tank is empty. BMW promises there will be ample warnings as the fluid level nears depletion.

Our brief drive of the 328d showed it to have the quiet and refined feel of most modern diesels. At cruising speeds, the diesel chatterings aren’t really audible unless the windows are down, and a relaxed rumble is perceptible under acceleration. Given the diesel’s tall gearing, you’ll find the engine spending most of its time between 1000 and 2000 rpm.

View PhotosMARC URBANO, THE MANUFACTURER

Less Peppy but Plenty of Thrust

Although it likely will be the slowest 3-series on the market—a 10th or two behind the upcoming 320i 2.0-liter gas turbo—the diesel is plenty quick for everyday driving, and its copious low-end torque makes off-the-line surges effortless. The powertrain is quite responsive unless you quickly slap your foot from the brake to the accelerator at a green light. That results in about a half-second delay before the boost picks up and the thrust begins. For critical launch situations, the astute driver will learn to brake-torque the 328d.

Interestingly, in Europe the 3-series with this engine is called the 320d, but in the American market it will carry 328i levels of equipment to justify its designation. Prices haven’t yet been set, but BMW says the 328d’s base price will be less than $40,000, which means about a $3000 bump over the cost of a 328i. The diesel will be available with xDrive all-wheel drive and in the 3-series wagon (xDrive only).

BMW plans to offer a new six-cylinder diesel in the 5-series at about the same time. That one will have 255 horsepower and about 400 lb-ft of torque. One can easily imagine these two engines eventually providing diesel options throughout BMW’s sedan and SUV lines. More than half of BMW’s European buyers already choose diesels. We’ll see how far the trend goes in America with broader availability of compression ignition in the lineup. Such a rollout is definitely in the cards.

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