When the Z4 roadster launched in 2003, no M version was planned. Into the breach stepped Alpina, the boutique manufacturer of BMW-based ultra-premium sports cars. To create its Roadster S, Alpina replaced the Z4’s M54 engine with its own S52-based E5/2, which used the US-spec engine’s cast iron block with larger bore diameters and a longer stroke for 3,346cc of displacement. Combined with an Alpina intake, exhaust, and electronics, the E5/2 delivered a sterling 300 horsepower and 267 lb-ft. That put the Roadster S firmly into M-car territory, but it achieved peak power and peak torque at lower rpm, making the Alpina especially user-friendly as well as quick. To improve upon the Z4’s rock-hard ride, the Roadster S paired supple Alpina suspension with conventional rubber in place of run-flats, here mounted on 19-inch wheels of the same design used by Alpina on its Z8-based V8 Roadster. That gave the car a high-end appearance that was well-matched by its luxurious interior. With fine leather throughout, the Roadster S was a clear step above any Z4, as its €54,950 price would indicate.
None of the 370 Roadster S models built from from July 2003 to December 2005 were sold in the US, but the car seen here remained in South Carolina following its tenure as the test and reference car for Alpina and BMW engineers.