Under the striking "flame surfaces" of the Z4 convertible resides the fabled, high-revving S54 inline-6 that powered the Euro-only BMW M3 CSL in 2003. This 343-hp power plant kicks the Z4 M into a completely new stratum of performance; and in keeping with the inspiration that made the M3 CSL such a lean and mean machine, BMW's M division stripped out the heavy electronics and driver aids that dulled the standard Z4's dynamics, leaving behind a stiffened engine bay, a sharper suspension, the exclusive variable M differential, and a notchy manual shifter with a direct clutch. The result is a car whose Spartan yet refined and comfortable interior lets you focus on the task at hand—taming a wild beast of a car whose extraordinary dynamic limits demand a firm grip.

The Z4 M's engine in stock form sounds mesmerizing pulling to 8,000 rpm—but it's just a little subdued for our tastes. We at PRI have taken it further with exhaust and induction tweaks bringing the output to a dyno-tested 360 hp. In many ways the Z4M is the last “pure” sports car to come from BMW, and the last to feature the inline-6 engine that traces its roots back nearly four decades.