Model history: During much of the 1980s, the rotary engined Mazda RX-7 was among the leading IMSA GT racers, racking up nearly 100 victories. The production based machine competed in the GTU class; the U was short for 'under' referring to the displacement limit of 2.5 and later 3 litre. Encouraged by the success of the GTU RX-7 and now with a suitable engine available, a fully fledged IMSA GTO (Over 3 litre) effort was readied for the 1990 season. Mazda in Japan provided technical support and, even more importantly, full funding for the campaign.
Originally the distinction between GTU and GTO had predominantly been the different displacement limits. Over time, however, the big manufacturers pushed the bar ever further and by the time Mazda joined, the GTO cars were effectively purpose-built, silhouette racers. Pretty much the only thing shared between the production and competition cars was the sheet metal of the roof. To provide some parity between the various engine types and sizes, the minimum weight varied from 860 kg (1,900 lbs) for the 3-litre cars all the way up to 1,200 kg (2,700 lbs) for the largest displacement permissible; 6 litres.
Mazda Japan supplied a batch of the four-rotor engine developed for the company's Le Mans campaign. Known as the '13J', it was effectively constructed by stacking two RX-7 production engines. Due to the nature of the rotary design, this was relatively easily done. The only issue was the longer eccentric shaft, which was prone to failure at very high revs. Equipped with the latest electronic injection system, the 13J produced 600 bhp and 529 Nm of torque in GTO trim. All this power was transferred to the rear wheels through a proprietary, Hewland five-speed gearbox.
Seasoned designer Lee Dykstra, of Jaguar Group 44 GTP fame, was hired to design a car around the 13J engine. He laid down an effective steel spaceframe chassis, clothed in carbon-fibre and aluminium panels. Although wider and lower, the body still clearly resembled the RX-7 road car. Suspension was by double wishbones all-round, with the front springs and dampers actuated by push-rods. Stopping power was provided by massive, ventilated AP disc brakes. Fully assembled the new RX-7 GTO tipped the scales at 1,020 kg or 2,250 lbs.
Run by Dick St. Yves, the Mazda USA team signed defending champion Pete Halsmer to drive the lead car while a second was fielded for Jim Downing. His Atlanta shop was also the base of the operation and he also served as team manager. With a class pole position in the 1990 Daytona 24 Hours, the RX-7 GTO had a spectacular debut. Unfortunately that car was forced to retire with engine problems, but the other survived to finish second in class. By the fifth round of the season, Halsmer scored the new Mazda's first victory. This win at Topeka was immediately followed by another a Mid-Ohio.
Halsmer's most significant win of the 1990 season was the GTO class victory at San Antonio; this was the 100th (class) win for the RX-7 in IMSA competition. Following the historic victory, Halsmer failed to add more to the GTO's tally but three wins in the debut season was far from disappointing. After the first few races, Downing had stepped out of the second car to concentrate on his managing duties. His first replacement was Mazda development driver Elliott Forbes-Robinson while later in the year 1990 Le Mans winner Price Cobb stepped in. For 1991, Cobb would join Halsmer permanently.
A year's worth of development really paid off in 1991 when Halsmer and Cobb dominated the IMSA GTO class. Halsmer took three victories, while Cobb added another two to the RX-7's tally. Even a 100 lbs weight penalty halfway through could not stop the Mazdas. Halsmer and Mazda ended the season as IMSA GTO champions. Halfway through the year work had started on an even more ambitious IMSA GTP campaign for 1992. Dykstra was once again responsible for the design, which also featured the all-new R26B engine, this time mounted amidships. The IMSA GTO effort ceased and the two cars were shipped to Japan.
Over two years later, Mazda dusted Halsmer's RX-7 GTO off for a 1994 Le Mans entry in the IMSA GTS class. Here it faced off against its old rival, the Nissan 300 ZX Turbo and eventually finished second in class and 15th overall. Later in the year, the car was also raced in the 1000 km sports car race at Suzuka. It briefly led before retiring. This would be the RX-7 GTO's final outing. Of the two cars built, one is in Japan and occasionally displayed. The other has been returned to the United States, where it was restored to full running order.
With the suspension of the GTO program at the end of 1991, the long and highly successful IMSA career of the RX-7 came to a close. With the help of private entrants, the type's final (class) victory tally is 106. Of these, eight were scored by the RX-7 GTO, which remains as the most extreme RX-7 based racing car ever built.
Chassis: GTO 001
Chassis '001' was the first of two GTO specification RX-7s built. It was used for two seasons by Pete Halsmer, making it the most successful of the two. Raced to six wins, this was the chassis that scored the RX-7's 100th victory. In 1994, chassis 001 was recommissioned and raced at Le Mans and Suzuka. It was subsequently sent back to Mazda USA where it was restored to its original configuration. At the 2011 Monterey Motorsports Pre-Reunion, it was raced in anger and still proved to be spectacularly fast.
Article by Wouter Melissen, last updated on February 02, 2012
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During much of the 1980s, the rotary engined Mazda RX-7 was among the leading IMSA GT racers, racking up nearly 100 victories. The production based machine competed in the GTU class; the U was short for 'under' referring to the displacement limit of 2.5 and later 3 litre. Encouraged by the success of the GTU RX-7 and now with a suitable engine available, a fully fledged IMSA GTO (Over 3 litre) effort was readied for the 1990 season. Mazda in Japan provided technical support and, even more importantly, full funding for the campaign.
