For , Honda switched their supply to McLaren and, encouraged by Prost, Dennis signed Ayrton Senna to drive. Despite regulations reducing the boost pressure and fuel capacity (and therefore, power) of the turbo cars, Honda persisted with a turbocharged engine. In the MP4/4, Senna and Prost engaged in a season-long battle, winning 15 of the 16 races (at the other race at Monza, Senna had been leading comfortably, but collided with back-marker Jean-Louis Schlesser). At the Portuguese Grand Prix, their relationship soured when Senna squeezed Prost against the pit wall; Prost won, but afterwards said, "It was dangerous. If he wants the world championship that badly he can have it." Prost scored more points that year, but because only the best 11 results counted, Senna took the title at the penultimate race in Japan.