“1989 was the first year where naturally aspirated engines were compulsory for all teams after the banning of the turbocharged units at the end of the previous season. To this end, Honda built a 3.5 litre V10 engine, developed throughout most of the latter half of 1987 and through 1988. The MP4/5 was unveiled for pre-season testing and it was instantly on the pace, as well as reliable. Developed by Neil Oatley, the MP4/5 looked like the car to beat in the new season. While the Ferrari that season was a fast all-around car particularly in the hands of Nigel Mansell, it was also chronically unreliable due to its new semi-electronic gearbox shift, giving further advantage to McLaren. The Honda-powered MP4/5 proved to have outright pace over the rest of the field, with 15 pole positions, 13 of them by Senna which equalled his 1988 record in the MP4/4. At the Mexican Grand Prix, Senna scored his 34th career pole in the MP4/5, breaking the previous record of 33 held by the late Jim Clark that had stood since 1968.

McLaren took 10 victories during the season, 6 for Ayrton Senna and 4 for Prost. This was at a time when the relationship between the two men was at its breaking point, so their rivalry pushed the development of the car far ahead of the other teams as they tried to out-do each other (although theirs was a very public rivalry, both actually worked well together in testing and Prost believes neither held back any information). Although Senna won six races to Prost’s four and usually finished ahead of the Frenchman in the races, accidents and car breakages meant that he had four fewer points-scoring finishes and finished 16 points behind his French rival in the championship.Senna and Prost’s combined points total meant McLaren easily won their second straight Constructors’ Championship.

Like 1988, the Drivers’ Championship was a two horse race between defending champion Senna and dual champion Prost. The championship was settled at the penultimate race in Japan. After dominating qualifying (with Senna predictably on pole), the two McLarens were evenly matched in the race and simply drove away from the rest of the field until their fateful collision at the chicane on lap 46. Prost was out on the spot while Senna was able to restart and after pitting for a new nose section, re-took the lead from the Benetton-Ford of Alessandro Nannini and went on to win the race. Ultimately, however, he was disqualified post-race for receiving a push start and missing the chicane after restarting which gave Prost his 3rd World Championship.

1989 was McLaren’s 4th Constructors’ Championship of the 1980s following on from 1984, 1985 and 1988, making the team the equal leading constructor of the decade with Williams who won in 1980, 1981, 1986 and 1987. It was also Honda’s 4th consecutive Constructors’ Championship as an engine manufacturer, and McLaren’s 5th Championship overall having won their first in 1974.”

– 1989: McLaren MP4/5, Wikipedia