 The next year, with turbos banned, Honda supplied a new 3.5-L naturally aspirated V10 engine and McLaren again won both titles with the MP4/5.Their drivers' relationship continued to deteriorate, though, especially when, at the San Marino Grand Prix, Prost felt that Senna had reneged on an agreement not to pass each other at the first corner.Believing that Honda and Dennis were favouring Senna, Prost announced mid-season that he would leave to drive at Ferrari the following year.