 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).