& Coupé. Z4 M versions The Z4 M Coupe/Roadster was introduced in 2006 and is powered by the S54 straight-six engine shared with the E46 M3. The S54 was also on the Ward's 10 Best Engines list for 2001 through 2004. The engine in the North American Z4 M models are rated at at 7,900 rpm, 3 hp less than the North American M3. In other markets, the power output is the same as the M3. The engine had BMW double VANOS system and a compression ratio of 11.5:1. The torque generated by the engine amounted to at 4,500 rpm. The torque was available from 2,500 rpm. The Z4 M uses hydraulic power steering, unlike the electric power steering used by the rest of the Z4 range. The Roadster used the E46 M3 steering rack, the Coupe the faster M3 CS/CSL rack. Other changes include a wider front track, revised front suspension, wider non-runflat-tires (measuring 225/45 at the front, 255/40 at the rear), and steering geometry. The brakes and the entire rear axle was too from the M3 CS/CSL. The M coupe's production began at the Spartanburg BMW plant in Greer on 4 April 2006. Special models Alpina Roadster S (2004–2006) The Alpina Roadster S is a high-performance iteration of the pre-facelift Z4 introduced at the 2003 Frankfurt Motor Show. Manufactured by German automobile manufacturer Alpina, the Roadster S was assembled at the manufacturer's Buchloe plant from body-in-white sent by the Spartanburg BMW factory. The Roadster S was produced for two years (2004 to 2005) before production was halted due to stricter emission regulations stopping engine supplies. The Roadster S was available in two trims, those being Standard and Luxury with the Luxury trim adding more creature comforts and bigger wheels over the Standard trim. The car had a claimed top speed of and accelerated to from a standstill in 5.3 seconds. The engine was modified by Alpina and change the name to E5/2. The engine create max output 300hp and max torque 362 Nm. Concept Coupé Mille Miglia (2006) The Concept Coupé Mille Miglia is a concept car inspired by the BMW 328 Mille Miglia Touring Coupé. It was unveiled at the 2006 Mille Miglia rally in Italy. Using the Z4 M Coupé's mechanical components, the concept car is longer, wider but flatter than the Z4 M Coupé. Other features of the concept car include 20-inch alloy wheels with