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  Mazda RX-792P

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Country of origin:Japan
Produced in:1992
Numbers built:3 (Only 2 were ever completed)
Designed by:Lee Dykstra and Randy Wittine for Mazda USA
Author:Wouter Melissen
Last updated:October 01, 2009
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Click here to download printer friendly versionWith the outright win at Le Mans and the IMSA GTO Championship winning run in North America, 1991 was certainly the most successful season of racing for Mazda to date. Inspired by these great results Mazda North America decided to move up the IMSA ranks by entering the Grand Touring Prototype (GTP) class in 1992. Here the Mazda team could go head-to-head with arch-rivals Toyota and Nissan. For the ambitious program a brand-new racing car was developed in-house around the four-rotor engine that had brought so much success in 1991. Headed by Lee Dykstra, of Jaguar Group 44 fame, the Mazda NA design team had already started their work in April 1990.

Primarily responsible for the development of the exterior design was Randy Wittine. He received instructions to incorporate as many style elements of the upcoming, third-generation RX-7 road car as possible. Wittine managed to include some small cues of the RX-7 but mostly the very smooth shape was dictated by function rather than form. The most striking features of the design are the scalloped panels behind the front wheels through which the air from the front diffuser exited. As with all GTP cars, most of the downforce was created by elements not visible to the eye. The full width front diffuser was one but even more important were the large ground-effects tunnels that ran on both sides of the cockpit and engine.

Dykstra focused on the design of the chassis and suspension. He penned a relatively straightforward carbon-fibre and aluminium honeycomb monocoque that was manufactured by Crawford Composites. It supported the front suspension that consisted of double wishbones and push-rod actuated springs and dampers that were mounted horizontally on top of the tub. At the rear much effort was made to keep as many suspension elements out of the ground-effects tunnels. Dykstra had no choice with the lower wishbones and driveshafts but did manage to mount everything else above the tunnel. This required a very unusual, horizontal, placement of the spring/damper unit.

Japan's main contribution to the project was the supply of the Le Mans winning four-rotor 'R26B' engine. This sophisticated rotary engine had also powered the 1991 IMSA GTO winning RX-7. Equipped with four variable intake trumpets, it produced at least 620 bhp. This power was transferred to the rear wheels through a March five-speed gearbox instead of the Hewland that had been used in the Group C cars. The very compact engine could not be mounted as a stressed part of the chassis. Initially Dykstra had intended to use carbon-fibre extensions to support the engine, gearbox and rear suspension but he eventually settled for a more conventional steel subframe.

Two examples of the aptly named RX-792P were constructed in a purpose-built facility. The first car was ready in time for the Miami Grand Prix at Homestead. The small team immediately faced two major exhaust related problems. The exhaust fumes proved to be so hot that the carbon-fibre tub start to delaminate. Eventually the car caught fire and was withdrawn. At the subsequent Sebring 12 Hours, the car was again not able to take part in the race. This time the problem was that the exhaust produced well over the 108 db noise maximum. Both issues were fortunately resolved by the third race. The muffler was coated on the inside and used air between its two layers to provide further insulation. A resonator was mounted that dealt with most of the noise and IMSA helped Mazda further along by placing the measuring device on the opposite side of the track from the RX-792P's exhaust.

By the third race, at Road Atlanta, the early problems were solved and the second car was ready. The RX-792P was now faced with an uphill battle against the NPTi Nissans and Eagle Toyotas, which both featured hugely powerful twin-turbocharged engines. For the first proper race, the fastest Mazda qualified 9th and finished a delayed 15th. Using their incredibly small budget, the team continued the development of the car and it soon sported a twin-tier rear wing, which increased the downforce considerably. The work yielded some results with 3rd and 4th place finishes at Lime Rock and a 2nd at Watkins Glen after starting from 4th on the grid. The season did not end very well with several non-finishes due to mechanical problems and accidents.

Undeterred by the mixed results, the Mazda North America team commenced preparations for the 1993 season. The third, spare tub was readied to receive a smaller three-rotor engine for a customer team, who wanted to run a Mazda in the IMSA Lights category. Unfortunately Mazda Japan had other ideas and ceased the rotary racing program at the end of 1993. By that time the unique engines had been banned from almost every other racing series, so it was not a complete surprise the plug was pulled. Built with a fraction of the budget ($5 million opposed to $20-35 million for the competition) the Mazda RX-792P fared remarkable well against the established teams and manufacturers. Whether it could have been a winner with more time and money, we will however never know.

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  Article Image gallery (23) Chassis (1) Specifications User Comments (1) Video (1)