The BMW Z4 is out of production, but Bovensiepen bought 99 of the final cars off the line and turned them into something special. At the Bernina Hill Climb, Andreas Bovensiepen walks us through everything that makes the Bovensiepen Spider different, then takes us for a ride up the pass. The exterior was reworked with Frank Stephenson Design. It gets new functional air outlets, a rear deck spoiler, and a front splitter, all tuned in the wind tunnel for aero balance. Under the hood, the 3.0-liter B58 inline-six now makes 435 hp. That comes from a ram-air intake hidden in the grille, a larger air filter housing, and a reworked exhaust with no particulate filter. Power goes to the rear wheels through the 8-speed automatic with paddle shifters. Other upgrades: 395 mm drilled front discs with Brembo calipers A 1,000-watt electric cooling fan A new aluminum rear differential cover with more oil capacity and cooling fins, which raises top speed from 260 to 295 km/h with the performance pack...