For , the M12 was upgraded into the M12/13/1. (Bore 9.2 mm X Stroke 60 mm) 374.95 cc and 350 PS per cylinder 933.46 PS/litre This version was claimed to have produced a maximum output of in qualifying trim, which would make it the most powerful engine ever to race in Formula 1, turbocharged or otherwise. At the time, there was no way to accurately measure horsepower figures over 1,000, and so claimed output figures were generally accepted from the engineers' theoretical calculations; for example, 0.1 bar of turbo boost was rated to be worth approximately ). During the 1986 Italian Grand Prix at Monza, Gerhard Berger's BMW-powered Benetton B186 recorded the highest straight line speed by a turbocharged Formula One car when he was timed at . In fact, the top five cars through the speed trap at Monza (Berger and teammate Teo Fabi, Brabham's Derek Warwick and Riccardo Patrese, and the Arrows of Thierry Boutsen) were all powered by the BMW M12.