March Engineering had been producing IMSA sports prototypes since the early 1980s with the 82G chassis. The 85G represented the culmination of that development cycle — a refined platform that the British constructor offered to customer teams across the highly competitive IMSA GTP category, where it faced factory efforts from Porsche, Jaguar, and Chevrolet-backed programmes.
The 85G used an aluminium monocoque chassis construction. A notable aerodynamic feature was a large ventilation opening between the headlights designed to direct airflow under the car to generate additional downforce, though in practice this effect was only partially achieved. Eleven chassis were manufactured in total.
The car was offered to customers who fitted a variety of different engines depending on their programme and resources. Conte and Ralf Sanchez Racing used a turbocharged Buick V6; the Leon Brothers Racing entry ran a Porsche flat-six; and DeAtley Racing installed a Chevrolet V8. This engine diversity was typical of the IMSA GTP class, which permitted a wide range of powerplants.
Three of the eleven chassis were sold to Nissan Motorsports International, marking one of the most significant customer relationships the 85G generated. Nissan used the cars in 1985 and 1986, racing them as the Nissan R85V. Two of the Nissan cars were fitted with V6 engines while the third received an inline four-cylinder unit, reflecting the company's testing of different configurations during their IMSA development programme.
The 85G was entered 94 times across 47 races during five years of competition — a substantial deployment for a customer chassis of its era. Despite this volume of entries, overall results were modest: the car recorded only one outright race victory and a total of five top-three finishes across its career.
The car made its racing debut at the 3 Hours of Daytona in 1984. Two examples were entered, but both failed to finish, a difficult start to the car's competitive life. Among the drivers who contested that debut event was Emerson Fittipaldi, marking one of the Brazilian champion's rare appearances in sports car racing.
The sole outright victory came at the 1985 Fuji 1000 km, a round of the World Sportscar Championship. Heavy rain caused most of the leading factory teams to withdraw from the event. The race was stopped early after only a quarter of the scheduled distance had been completed due to an impassable track, and at that point the Japanese trio of Kazuyoshi Hoshino, Akira Hagiwara, and Keiji Matsumoto were leading in their 85G and were declared the winners.
The March 85G occupies a modest but notable place in IMSA GTP history as the final expression of the 82G lineage and as the platform that gave Nissan its first structured American endurance racing programme. Its single outright victory came under exceptional circumstances, and its overall results were limited by competition from factory-backed machinery. Nevertheless, eleven chassis in customer hands across five seasons of competition testifies to the car's viability as an independent package in one of the most demanding prototype categories of the 1980s.