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Driving Impressions
The 2007 BMW 3 Series coupe represents the newest and fifth generation of a vehicle that traces back nearly four decades to the BMW 2002, one of BMW's most famous cars and which many consider to be the original European sports sedan (in this case, sedan means four- or five-passenger car with a fixed metallic roof, as opposed to a two-seat roadster or convertible).
The new 335i is the first BMW in some 25 years to have a turbocharged engine. BMW was committed to increasing on the 255 horsepower provided by the inline six-cylinder engine used in the previous 3 Series coupe. One way would have been to switch to a V8, but BMW opted to another solution, one that would combine the power of a V8 with the fuel economy of the inline-6.
That solution was to develop an engine that incorporated two small turbochargers, fan-like devices that boost the air pressure within the engine to enhance the fuel combustion cycle, therefore getting more power without increasing the number of cylinders. Another drawback BMW saw with the V8 was that it would be heavier, and would add weight to the car's nose, which does not help the sort of dynamic handling qualities on which BMW has built its reputation.
The key to the twin turbo engine's performance isn't just its forced induction system, but also the engineers use of special and so-called piezo fuel injectors. By precise control of the air/fuel mixture and its placement within the cylinder, BMW is able to optimize the engine's performance not just in power output but also in fuel economy and in a reduction of as much as 20 percent in harmful exhaust emissions.
Even while delivering 300 horsepower, the twin turbo engine is rated at 19 mpg in the city and 28 on the highway with the manual transmission and at 20/29 mpg with the automatic. To put those figures in context, the 230-hp engine in the new 328i, which does not have the special injectors, is rated at 20/30 in fuel economy.
Turbocharged engines often have what is known as turbo lag, a period of hesitation between the time the driver tips into the throttle and the time the turbocharger spools up to boost the power. To the driver, it feels as though nothing is happening, and then suddenly the engine explodes into action. But by using two smaller turbos, and by keeping them turning even at slow speeds, BMW was able to fine tune the system to eliminate lag. Instead, power is provided in a smooth and linear delivery as the needles on the tachometer and speedometer sweep their arcs across their respective dials.
By spooling the turbos earlier, maximum torque is achieved at just 1400 rpm and holds steady all the way to 5000, just about the point at which horsepower is reaching its peak. Thus this six-cylinder engine has torque delivery much like that of a V8. While we enjoy shifting gears, the engine is strong enough that on our drive on wonderful winding roads through the hill country between San Francisco and Bodega Bay in northern California, we could be content to simply pick third or fourth, depending on the speed we wanted to travel, and enjoy the scenery while the engine's broad power band kept the car's momentum flowing.
After driving a 335i with a manual transmission in the morning, we switched after lunch to a 335i with the automatic transmission, one equipped with paddle shifters on the steering wheel. Again, we found the car very responsive even when we let the transmission shift on its own. For those who like paddle shifting, BMW notes that it had cut the transmission's response time to the paddles in half to enhance the driver's sense of control.
To make sure power is used most efficiently, BMW uses different transmissions for different 3 Series coupes. The 328i has either a Getrag I manual or GM-sourced automatic. The 328xi gets a Getrag H manual or the GM automatic. The 335i has either a ZF Type G manual or a ZF high-performance 19 TU automatic.
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