The McLaren MP4/8B was powered by a Lamborghini V12 and driven by Ayrton Senna in September, 1993 at Estoril after the Portuguese Grand Prix. It was faster, and he wanted to race it in Japan. That never happened.
At some point earlier in 1993, Bob "Maximum" Lutz and Ron Dennis shook hands. Lutz was Chrysler's chief executive and Lamborghini was part of their portfolio since 1987. And while they already supplied the 'Lamborghini 3512' V12 to the Larrousse F1 team, he wanted to win races with it. He needed a top team for that, and Ron Dennis happened to have one.