BMW introduced an M version of the E85 Z4 in late 2006. Called the M Roadster, it's powered by the same 3.2L, 8,000rpm, S54 inline-6 engine as the E46 series M3, delivering 330hp through a manual gearbox and a new 6-speed manual transmission. Engine management is via the Siemens MS S70 with higher processing power (64 million calculations per second) than the MS S54 (25 million CPS) in the M3. Other performance parts borrowed from the M3 include the CSL's compound (aluminum hubs, iron floating rotors) brakes and most of the M3's suspension components. Other changes include a hydraulic steering setup which provides better feel than the electric system in standard Z4 models. Weighing 3197 lb (1450 kg), the M Roadster has been tested by major U.S. car magazines to accelerate from Zero-60 mph in 4.7 seconds, which is slightly quicker than the Porsche Boxster S and Porsche Cayman S. Top speed is electronically limited to 155 mph (249 km/h).