BMW Z4 M, minus the M

BMW shows off a tweaked version of its Z4 roadster at the 2010 Detroit auto show.

BMW Z4
BMW cranks even more power out of the twin turbo-charged engine in its Z4. BMW

The BMW Z4 sDrive35i is an excellent sports car. However, BMW's engineers, who must experience self-critical dreams every night about how much smoother a valve could be or whether changing the timing of a spark by a millisecond might improve combustion, couldn't leave it as is. They developed the 2011 BMW Z4 sDrive35is, a higher performance version of BMW's roadster.

Like the sDrive35i, the new roadster uses a twin turbo 3-liter straight six cylinder, but BMW fitted it with a new twin turbo unit to crank up the horsepower from 306 to 335, with torque up from 295 pound-feet to 332 pound-feet. This engine tweaking gives the sDrive35is acceleration to 60 mph in 4.7 seconds.

Beyond the engine work, BMW tuned the exhaust to give a more pleasing, sports car sound. Baffles and mufflers combine to give the car what BMW describes as a "deep rumble with a focus on the low frequency sound range." People will be surprised when they see a little roadster following that exhaust note as it works its way up the street.

The sDrive35is also gets BMW's seven-speed double-clutch transmission, a manual with two computer-controlled clutches. The driver can choose an automatic mode or shift manually, but doesn't have to push a clutch pedal. The result is no power loss at the wheels during shifts.

You can even get the car with some M equipment, including an adaptive suspension that uses electronically controlled shock absorbers to counteract roll and keep the tires gripping pavement. That's a lot of tech in a little car.

BMW will show the Z4 sDrive35is at the upcoming 2010 Detroit auto show.

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