2007 BMW 3-series

Engines

Expanded lineup, more power

The 325i and 325xi Sedans and 325xi Sports Wagon are now replaced by the rear-wheel drive 328i Sedan and 328i Sports Wagon and the all-wheel drive 328xi Sedan and Sports Wagon, powered by a new version of BMW’s 3.0-liter inline 6-cylinder with aluminum/magnesium engine block, producing 230 horsepower and 200 lb-ft of torque; a + 15 hp and + 15 lb-ft of torque improvement over the previous models.

The 330i Sedan is replaced by the 335i, featuring the 3.0-liter twin-turbocharged inline 6-cylinder engine with a cast aluminum engine block producing 300 horsepower and 300lb-ft of torque. This is a + 45 hp and + 80 lb-ft of torque improvement over the 2006 model.
The increase in horsepower and torque on both of these engines is not offset by a decrease in fuel efficiency. The new engines have similar fuel economy as the already impressive 2006 3 Series Sedans and Sports Wagons.

Drivers may specify the standard-equipment 6-speed manual transmission or the optional 6-speed STEPTRONIC automatic transmission. The328i gear ratios remain the same as the 2006 325i. The 335i gear ratios have been optimized to work with the new twin-turbocharged engine. The 335i Sedan also has steering wheel-mounted paddle shifters when ordered with the optional Sport Package and STEPTRONIC automatic transmission.

BMW twin-turbo 6-cylinder engine
It is the most powerful engine within BMW’s wide range of inline 6-cylinder engines that does not wear an "M" badge. The twin-turbo engine, designated N54, develops a maximum output of 300 horsepower in US specification from 3.0 liters displacement and generates peak torque of 300 lb-ft for powerful acceleration in any situation. And it achieves these results using technology that might surprise students of BMW history: turbocharging.

Although it is standard equipment on BMW’s highly acclaimed diesel engines, BMW has not used turbocharging with a road-going gasoline powerplant since the 1980’s. Until now, the BMW 745i Sedan, which debuted in 1981, and the iconic BMW 2002 Turbo, introduced at the 1973 Frankfurt auto show, were the only two standard-production, gasoline-powered BMWs to employ the technology.

Although the technology works as advertised, BMW engineers were not satisfied with the most-often cited downside to turbocharging: the frustrating lag between when the driver presses the accelerator pedal and when the turbocharger develops sufficient rotation to increase power. This lag is at its worst low engine speeds. Other drawbacks included relatively high fuel consumption and available materials that did not always fare well under the high-heat, high-rpm operation of the turbocharger, which gets its energy from hot exhaust gases and typically spins up to 5-figure rpm’s. For these and other reasons, BMW put turbocharged gasoline engines on the shelf or more than 20 years.

Two recent developments caused BMW to reconsider turbocharging: a trend among many luxury-performance carmakers to achieve power gains by building engines of ever-increasing displacement and technology transfer from turbocharged diesel engine development to their gasoline-fired counterparts.

Accordingly, BMW recently articulated its new approach to developing high-performance engines as part of its EfficientDynamics initiative. Beginning with the N52 normally aspirated engine and the N54 turbocharged unit, BMW will achieve its performance goals with smaller, lighter, more efficient and cleaner-running engines.

The N52 features twin, relatively small turbochargers to boost performance significantly, but, at the same time, minimize turbo lag. Thanks to their lower inertia, two small turbochargers build up pressure much faster than a single, large turbocharger, thus eliminating even the slightest lag.

The front turbocharger feeds cylinders 1 - 3; the rear unit delivers super-compressed to cylinders 4 - 6.

A further in advantage of turbocharging is that this is the most weight-effecient to boost engine power and performance. The N54 turbocharged inline engine weighs approximately 150 lbs. less than an equally powerful eight-cylinder engine displacing 4.0 liters. This lower weight means a significant advantage not only in fuel economy, but also in balancing the car’s weight distribution.

To enhance efficiency, the turbochargers are made of a particularly heat-resistant material which makes them immune to high exhaust gas temperatures in the interest of a fuel-efficient combustion process particularly under full load.

As a result, the twin turbo technology in the BMW 335i Sedan and 335i Coupe represents a significant achievement in terms of both performance and fuel economy. The advantages over a conventional turbocharged engine are not only clearly measurable, but easy to feel on the road.

This new high-performance engine develops its power and performance much more spontaneously than a turbocharged engine of conventional design. At the same time, the N54 engine offers all the smoothness and refinement which made BMW’s award-winning inline sixes so admired well. Last, but certainly not least, the impressive increase in power on the twin-turbo engine versus a normally aspirated six-cylinder engine comes without any significant increase in fuel consumption.

Turbocharging typically includes intercooling of the engine’s induction air, in other words, cooling the compressed air heated by the combustion process, from the turbocharger(s). Sometimes that’s accomplished with coolant; in the case of the N54 engine, it’s accomplished with outside air. Intercooling is desirable, often necessary to reduce the temperature of the incoming air to preclude detonation or "knocking" that can reduce power or, in the extreme, damage the engine. Of course, the N54, like the normally aspirated N52 and other current BMW engines, is equipped with knock control.

As effective as the magnesium/aluminum engine construction is for saving weight, the significantly increased loads and cylinder pressures of the N54 300-horsepower engine required the use of an aluminum engine structure with cast-iron cylinder sleeves. Some, but not all, of the N52’s magnesium/aluminum weight saving was lost in this process. All together, the N54 weighs 419 lb; the N52 357.

A new high-pressure direct fuel injection system utilizing so-called piezo injectors also enhances performance and fuel efficiency. A 2nd-generation evolution of the system found on the BMW 760’s V12 engine is a key factor in achieving BMW’s goals for the N54. The new system’s in advance over its predecessor is that it provides the engineers a greater degree of freedom in the calibration of fuel quantity and timing and the distribution of the fuel-air mixture in the combustion chambers.

A piezo injector, a recent advancement in fuel injector technology, uses an actuator that takes the place of the solenoid valve in a conventional injector. The actuator, which works significantly faster than the solenoid, reduces the injector’s response time. That results in, according to researchers who led the piezo injector’s development, a 2 - 3% fuel savings and 20% less emissions. 

For the first time in a 3 Series Sedan, the exhaust pipes run under both sides of the vehicle from the engine compartment to under the rear bumper, creating a true dual exhaust system. At low loads, a flap channels most exhaust gases through one side to reduce low-frequency exhaust "rumble."

Performance improvements
The new engines deliver impressive 0-60 mph acceleration performance improvements, specifically:

• 328i Sedan - 6.3 sec. (manual) 6.9 sec. (automatic) - 0.4 sec./0.3 sec. improvement

• 328xi Sedan - 6.9 sec. (manual) 7.1 sec. (automatic) - 0.2 sec./0.6 sec. improvement

• 335i Sedan - 5.4 sec. (manual) 5.6 sec. (automatic) - 0.7 sec./0.7 sec. improvement

• 328i Sports Wagon - 6.5 sec. (manual) 7.1 sec. (automatic) - New model

• 328xi Sports Wagon - 7.1 sec. (manual) 7.3 Sec. (automatic) - 0.2 sec./0.6 sec. improvement
  

Interior

Driving and chassis