The Z4 M40i's smoothness starts with geometry, not electronic trickery. Its inline-six engine, which helps propel the roadster from rest to 100 kilometers per hour in a stated 4.6 seconds, arranges six cylinders in a single row. That arrangement gives the engine an advantage before a single spark is fired.The real elegance lies in cancellation. Pistons move in matched pairs, and their crankshaft p...More