and there were only 22 starters. Qualifying also saw the FIA's controversial pop-off valves used for the first time on the turbocharged cars. The valves limited turbo boost pressure to 4.0 Bar where previously boost was only limited to what the engineers felt the engines could take. The valves were far from popular with the teams and drivers, however, with some drivers complaining throughout the weekend that they were cutting in too early and not allowing enough boost. Arrows driver Derek Warwick told that at times his valve was opening at just 2.6 Bar (a loss of approximately ) while Benetton's Thierry Boutsen told that the two valves on his Ford V6 were both opening at different levels and both well below the 4 Bar limit. McLaren got around the pop-off valve problem by limiting turbo boost on their TAG-Porsche engines to just 3.6 Bar of pressure throughout the weekend, thus never allowing the valves to come into play. One unnamed team mechanic was reported to have said that the valves were the only crude piece of engineering on a modern Grand Prix car. The Ligier team was absent from Rio, missing their first race since the French boycott of the 1985 South African Grand Prix. The team had been set to use a new 4-cylinder, turbocharged Alfa Romeo engine for the season. However, during pre-season testing lead driver René Arnoux compared the new 415T to used food. This gave Alfa's parent company Fiat the excuse they wanted to pull out of its association with the team leaving Ligier without an engine for the season, though Ligier were able to secure a supply of Megatron turbo's from the Arrows team sponsors USF&G and would use them from San Marino until the end of the season. Race At the start Piquet was fastest, taking the lead from Senna, while Mansell made a bad start; the Benetton B187s of Boutsen and Teo Fabi out dragged Mansell and Prost. Adrián Campos was disqualified for an incorrect starting procedure, he had forgotten his ear plugs and by the time he had fitted them on the grid the rest of the field had moved away on the warm-up lap. Campos resumed his grid position instead of starting at the rear, and race officials removed him for his rookie mistake. Piquet's lead did not last long: on lap 7, he had to pit with engine overheating