The engineering wizards at BMW’s high-performance M division have worked their magic again—this time producing a souped-up version of the M4 coupe introduced last year. Making its world debut at the Pebble Beach Concours d’Elegance, the BMW Concept M4 GTS is a performance beast, equally at home on the road or the racetrack. The M4’s 425 hp, turbocharged engine gets a boost thanks to a new water-injection system that sprays a fine mist into the intake manifold, cooling the air and resulting in an increase in po…