The 2009 Detroit auto show saw the reveal of the gorgeous BMW Z4 roadster, one of the best recent designs to come from the company. In nearly a year since then, we’ve also been impressed with the car dynamically, awarding it a second-place finish in our most recent comparo of four luxury droptops, just behind our longtime favorite Porsche Boxster S. For the 2010 Detroit show, BMW is bringing along a new range-topping Z4, one with a massaged engine, subtly modified looks, and a load of M Sport touches.

Just when we thought BMW’s convoluted naming scheme couldn’t get any longer, the company resurrects the “is” suffix and tacks it onto the sDrive35 badge. We're surprised the company didn't call it a Z4 M. Until this year, BMW M cars all had engines distinct from those in standard BMWs, but the X5 M and X6 M—which share the guts of their V-8s with more pedestrian BMW models—have already crossed that line.

More Power From the Turbo Six, Not That it Needed Any

Tuners have proven it time and again: the twin-turbo BMW inline-six is capable of more than the factory-provided 300 hp and 300 lb-ft of torque. BMW is now ready to admit as much, apparently, and has given the engine better intake breathing and higher boost pressure for new output of 335 hp at 5900 rpm and 332 lb-ft from 1500 rpm, with overboost providing quick bursts of 369 lb-ft. A specifically tuned exhaust system is promised to provide a “deep rumble with a focus on the low-frequency sound range.”

Transmission options number one; the sDrive35is will be available only with BMW’s seven-speed double-clutch transmission. Here, it features a dual-mass flywheel to handle the increased power. The programming is also unique to the model. Gear changes can be effected either via the console selector or wheel-mounted paddles. Launch control is part of the package, as well.

BMW estimates a 0-to-60-mph time of 4.7 seconds—we’ve seen 4.8-second runs from a standard sDrive35i and wouldn’t be surprised if the sDrive35is can manage the task in something closer to 4.5 seconds. (Incidentally, that would put it ahead of the now-defunct, 320-hp Z4 M roadster’s time of 4.6 seconds.) Top speed is electronically limited to 155 mph. What’s more, BMW expects the 35is car to match the EPA mileage rating of the 35i with dual-clutch transmission—17 mpg city/24 highway. We expect real-world mileage will suffer a bit, though, especially with our feet on the pedals.

The Z4 35is gets unique, sporty programming for its electric power steering system. We’ve derided this system in the standard car, calling it vague and lacking in feedback. Hopefully the new programming will bring back some of the feel as claimed. Driving Dynamics Control, included on other Z4 models, allows the driver to adjust between normal, Sport, and Sport+ settings for shift speed, throttle sensitivity, and the adaptive M suspension, which also comes standard on the sDrive35is.