Page 1 of 2 Next >> 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. Page 1 of 2 Next >>