With ground effect banned at the end of 1982, the RE40 was built around a flat-bottomed arrangement and featured enlarged wings to recover as much downforce as possible. It was the first Formula One car to route its exhaust in a manner that increased diffuser downforce — a significant aerodynamic innovation. The RE40 was also the first Renault chassis built entirely of carbon fibre; construction was outsourced to aerospace specialists Hurel-Dubois. A small aluminium crash box at the nose allowed easy repair after minor impacts, while the overall structure was deliberately overbuilt for strength following Didier Pironi's career-ending accident the previous year.
Power came from Renault's Gordini EF1 turbocharged 1.5-litre V6, the same fundamental unit that had debuted in the Renault RS01 in 1977 and earned the distinction of being the first turbocharged engine to win a Formula One Grand Prix. In twin-turbo form — one turbocharger per cylinder bank — the RE40's engine produced a claimed 750 bhp in qualifying trim and around 650 bhp in race configuration. However, the turbochargers proved to be the car's primary weakness throughout the season: Prost later recalled that "that year there was a good turbo to have and a bad one. We had the bad one."
The driver lineup changed significantly from 1982. René Arnoux departed to Ferrari, replaced by American Eddie Cheever. With Cheever accepting a number two role, Prost was the undisputed team leader and the car was designed around his driving style; he accumulated extensive pre-season test mileage to minimise the reliability issues that had plagued Renault in previous years.
The RE40 made its Grand Prix debut at the 1983 US Grand Prix West at Long Beach, where an inauspicious debut saw Prost qualify eighth after a persistent misfire and finish eleven laps down in eleventh place. The car's form improved quickly: at the following French Grand Prix at Paul Ricard, Cheever started second while Prost took pole and won.
Prost scored consistently across the season, taking four victories. He led the drivers' championship for most of the year, ahead of Arnoux at Ferrari and 1981 World Champion Nelson Piquet in the Brabham-BMW. The RE40 was best suited to fast circuits — Spa-Francorchamps, Silverstone, and the Österreichring all yielded wins for Prost — though a DNF at Monza denied him a potential sweep of the high-speed venues.
The championship came down to the final round in South Africa. Ferrari's Ferrari and BMW's engine were both believed to have a power advantage, with the Ferrari producing around 800 PS and the BMW approximately 850 PS in qualifying trim against the Renault's 750 PS, though all three manufacturers de-tuned to roughly 650 PS for race conditions. Needing points to secure the title, Prost's turbocharger failed and Piquet won the race, taking the championship by just two points.
Cheever proved a reliable and harmonious team mate, scoring several podiums, though turbo reliability issues repeatedly prevented him from converting strong positions into victories. Overall the RE40 took four wins and three pole positions in 1983.
Prost, frustrated by Renault's inability to mount a consistent championship challenge, publicly criticised the team's development effort at season's end and was sacked. He joined McLaren, where he would win his first World Championship in 1985. Cheever also departed, joining Alfa Romeo.
Despite the season's near miss, Prost later spoke warmly of the car: "a lovely car... we should have been World Champions 10 times over." Prost's win at the Austrian Grand Prix proved to be the final victory for Renault in their original works Formula One programme; the team failed to win again in 1984 or 1985 before withdrawing from Grand Prix racing as a constructor at the end of 1985. The RE40 was succeeded by the RE50 from the first round of 1984.
The RE40 marked several technical milestones: the first all-carbon-fibre Renault chassis, the first use of exhaust-blown diffuser aerodynamics in Formula One, and the car in which Renault came closest to claiming a drivers' championship in their original works team era. Its 1983 season remains one of the most compelling near-misses in the sport's history, with a talented driver and a genuinely competitive package falling short through mechanical fragility rather than pace.