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Engines
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Smooth and powerful 6-cylinder engines
In a sea of V-6 engines, BMW swims almost solo with its unusual - but in BMW's opinion superior - inline-6 configuration.
The Z4 is powered by two versions of the current M54 6-cylinder engine family, of which Car and Driver wrote this in naming the 3 Series to its annual 10Best list in January '02: "Then
there are the magical 6-cylinder power trains that spin with velvety smoothness while delivering thrust completely disproportionate to their size."
In addition to its six cylinders inline, this brilliant engine architecture features:
- Aluminum construction, contributing to vehicle performance by keeping down engine weight.
- Dual overhead camshafts and four valves per cylinder, for optimum torque and power.
- Chain camshaft drive, requiring no periodic replacement.
- Double VANOS steplessly variable valve timing, enhancing torque, power and emission control.
- Hydraulic valve adjustment for consistent sound and reduced maintenance.
- Electronic throttle system ("drive by wire") for smooth, precisely tuned throttle action and seamless integration of cruise control, Dynamic Stability Control and other features. This
also facilitates an appealing option: Dynamic Driving Control, about which more later.
- Electronically controlled engine cooling, enabling precise and purposeful control of engine temperatures; contributes to fuel efficiency and heater effectiveness.
With all these elements of engine architecture shared, two versions of this power plant power the two Z4 models:
Z4 2.5i. 2.5-liter, with 184 horsepower and 175 lb-ft. of torque. This "entry-level" power plant provides performance that's anything but entry-level. Though these official power and
torque ratings are unchanged from earlier versions of this engine, fine-tuning of the intake system and a new exhaust system enhance its response at low to medium speeds. In a June 13, 2001 comparison test of the BMW 325i sedan against key V-6
competitors, Germany's respected auto motor und sport magazine raved: "The BMW engine is in a class by itself, with six cylinders in a row in a time of V-6s. Inline sixes take up a lot of space and are relatively costly, but in terms of
balance they are the ideal engine type. The BMW proves this convincingly: light-footed, vibration-free revving, spontaneous response, and a sound that is not quiet but is outright pleasant." In the Z4 2.5i with manual shift, this unit delivers
0 to 60 mph in 7.1 sec. and achieves the amazing top speed of 146 mph. Its projected EPA mileage ratings are impressive too: 21-mpg city/28-mpg highway with the optional automatic transmission, 20/28 with the 5-speed manual.
Z4 3.0i. 3.0-liter, with 225 hp and 214 lb-ft. of torque. This version is further refined for an even more exciting sound. "One punch of the throttle tells you the larger 3.0L version
of BMW's stellar inline-6 is a masterpiece: sultry, sinewy, sonorous," commented Motor Trend on the 330i sedan's similar engine in its May '01 issue. It powers the Z4 3.0i to 60 mph in just 5.9 sec.; top speed is electronically limited to 155
mph. With its standard (and new) 6-speed manual transmission (available in December production), the Z4 3.0i earns excellent projected EPA mileage ratings of 21-mpg city / 29-mpg highway; with automatic it tests at an impressive 20/28.
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