When Formula 2 was replaced by the new Formula 3000 category in 1985, Ralt entered with the RB20, a development of the successful Honda-powered RH6 works Formula 2 cars fitted with a Cosworth DFV engine. The RB20 won four races in the inaugural International Formula 3000 season with Mike Thackwell and John Nielsen. For 1986, however, Ralt sought to offer a more economical and customer-friendly option alongside its works programme, producing the RT20 with a conventional aluminium monocoque rather than the honeycomb construction used in the works machinery. The simpler structure made the car less expensive to acquire and repair, lowering the barrier to entry for smaller teams competing in the growing Formula 3000 grid.
In the 1986 International Formula 3000 Championship, the RT20 competed under two distinct programmes. The Ralt works team ran Honda-powered RT20s, while customer teams used Cosworth-engined versions. The works effort secured one race victory with Mike Thackwell, the experienced New Zealand driver who had driven Ralt's works Formula 2 cars to championship success in 1984. Customer teams proved capable of strong results as well: the Italian Pavesi Racing team ran Pierluigi Martini and Luis Pérez-Sala in Cosworth-powered RT20s, and together they won four races between them across the season, making the customer programme arguably more prolific in victory terms than the works effort.
The RT20 was followed for 1987 by the RT21, which incorporated honeycomb elements into the monocoque and continued with Honda for the works team. Roberto Moreno and Maurício Gugelmin each took a race victory in the RT21 that season. Ralt continued developing its F3000 cars through 1988 with the RT22, its first carbon-fibre F3000 chassis, before selling the company to the March Group in the autumn of that year.
After the RT20's Formula 3000 career, second-hand examples found competitive use in Australia's Formula Holden category, which was introduced in 1989 using retired F3000 machinery fitted with a 3.8-litre Holden V6 engine in place of the original Cosworth unit. Rohan Onslow won the 1989 Australian Drivers' Championship in an RT20, giving the chassis a championship-winning record in a second country and a second formula. The RT21 also won the 1990 Australian Drivers' Championship with Simon Kane, demonstrating the longevity of the Ralt F3000 design in Australian domestic competition.
The RT20 represented Ralt's attempt to balance works competitiveness with the commercial needs of a customer car programme in Formula 3000. Its aluminium tub philosophy, while less technically advanced than the honeycomb works cars, proved well suited to the budget constraints of customer teams and extended the manufacturer's reach across the F3000 grid. The four customer victories achieved by the Pavesi Racing team in 1986 remain notable as evidence that the customer specification car was genuinely competitive rather than merely a commercial offering. The RT20 forms part of the sequence of Ralt F3000 designs — RB20, RT20, RT21, RT22, RT23, RT24 — that marked the manufacturer's final years as an independent constructor before absorption into the March Group.