What is it? BMW has taken the already sporty twin-turbocharged Z4 and bumped it up a notch, moving it toward performance territory normally reserved for cars with the M (motorsports) badge. The addition of the small "s" suffix to the sDrive35i brings more horsepower and torque to an already quick car. BMW has improved intake air flow and increased boost pressure from the 3.0-liter, twin-turbocharged six-cylinder in the sDrive35i. In "is" guise the engine produces 335 hp and 332 ft.-lbs. torque, and it is mated to a standard seven-speed dual-clutch transmission. Acceleration from 0-60 mph takes 4.7 seconds, according to BMW, and top speed is limited to 155 mph.
The sDrive35is has an electronically-controlled adaptive suspension that drops the car 0.4 inches lower than the standard sDrive35i, and it visually differs from the regular car with the addition of BMW M Sport aerodynamic parts.
What is new or notable? The engine features an electronically-controlled overboost feature that can briefly increase torque to 369 ft.-lbs. under full throttle.
CR's take: BMW may not be offering an M version of the Z4 right now, but with the various M-logo bit and pieces, this is as close as enthusiasts will get to a Z4M.
When will it be available? Spring 2010.