BMW’s 335d model was introduced to the US marketplace in 2009. As you’ve probably already surmised, the lowercase “d” in the model’s nomenclature indicates the BMW 335d powerplant runs on diesel fuel. While this was a new development for the US marketplace, BMW diesels had been sold in Europe for a number of years before the company tried marketing a diesel-powered model here.
While there are obvious efficiency benefits to running diesel power, there was considerable concern over offering anything other than a gasoline-fired engine in the States because of BMW's reputation for performance. And, while there is still a bit of stigma to overcome regarding diesel-powered cars for Americans, the 335d’s numbers make those old stereotypes rather difficult to cling to.
The turbocharged inline six-cylinder engine fitted to the 2009 BMW 335d produced 265 horsepower and 425 ft-lbs of torque. A six-speed automatic transmission (with a sport mode) sent the power to the rear wheels. Further, the engine generated its full 425 ft-lbs of torque at 1,750 rpm. In other words, pretty much the moment you nailed the throttle you had full access to the entire well of torque reserves. Additionally, the full 265 horsepower came on line at 4,200 rpm, so the engine didn’t run out of breath at high speeds.
This was largely accomplished through direct fuel injection, variable valve timing, and the employing of twin-turbocharging. Using this scheme, a smaller turbo could be fitted to provide quick response, while a larger one was also in place to produce the massive torque number. This strategy enabled the BMW’s engineering team to take advantage of the gains provided by turbocharging, while avoiding the pitfall of turbo lag.
In a single large turbo configuration, the engine must often wait for the turbocharger to come up to speed before the benefits can be realized. Whie a smaller turbocharger spins up faster and becomes effective much sooner—it runs out of boost potential fairly quickly.With a staggered size twin-turbo strategy, by the time the smaller unit is beginning to lose effectiveness, the larger turbocharger is kicking in to take up the slack.
In addition to providing substantial power increases, turbocharging also reduces fuel consumption and particulate emissions. You get more power from less fuel and the engine runs cleaner besides. The gains are even more significant when you consider a diesel engine inherently returns better fuel economy than a similarly sized gasoline engine. Thus, with the BMW 335d, the company offers a cleaner-burning, more fuel-efficient automobile, with very nearly the same performance potential as the gasoline fired version of the BMW 3 Series sedan.