The 1989 season saw a host of regulation changes, the major of which was ending the turbocharger era in Formula One. New naturally aspirated 3.5 litre engines were to be used. Despite Ferrari winning the 1989 Brazilian Grand Prix, McLaren-Honda continued their previous season form. Both Senna and Prost traded wins throughout the season, with the Ferraris on some occasions managing to challenge the powerful Honda V10 McLarens. The first issues began to arise in the McLaren garage at the 1989 San Marino Grand Prix. Prost highlighted his discontent with Senna, resulting from an agreement in which whoever won the start off the line, would not be challenged into the first corner at Tosa. At the restart, Senna passed Prost into Tosa after Prost got into the lead from the start and went on to win by over a minute. Marlboro's John Hogan was in support of Prost's proposed agreement, with Senna denying such an agreement was ever made.