NAIAS Highlights: Concepts
Mazda's RX-8
When Mazda President and CEO Mark Fields unveiled the RX-8 concept, it brought the automaker one step closer to production of a high-performance four-door sportscar with a rotary engine. "I wouldn't be surprised if you see this car - or something very close - on some of the world's most scenic, most fun-to-drive highways in the not-so-distant future," he said.
The RX-8, powered by a 186 kW (250-hp) engine driving the rear wheels, is "much closer" to an actual production sportscar than its predecessor, the RX-EVOLV concept car that was introduced at the October 1999 Tokyo Motor Show, according to Mazda. It has a compact-looking body, while providing enough interior room to seat four adults comfortably.
The RENESIS engine, introduced in the RX-EVOLV, is naturally aspirated and 30% lighter and more compact than the turbocharged rotary engine (13B-REW) in Japan's RX-7. With its side intake and exhaust ports, the engine provides good fuel economy and low emissions. The engine block is 338 mm (13.3 in) high - about the same height as the transmission - and 60 mm (2.4 in) closer to the center of the body than is the RX-7's.
The engine's light weight, small size, low center of gravity, and positioning in the vehicle enhances the RX-8's maneuverability and high-end performance. It reduces the low inertia moment in turns by up to 15%. A low hood, short overhangs, and interior room on par with a sports sedan are benefits of the engine's configuration and layout. The engine layout, along with a 50:50 front/rear vehicle weight distribution, enhances control and handling.
With further work, the engine will have power levels up to 209 kW (280 hp) at 9000 rpm.
By positioning the powertrain lower, RX-8 engineers were able to improve rigidity by locating a high-mount backbone frame on the upper part of the tunnel. The frame connects the front and rear bulkheads through the inner center. It also functions as a main body frame element, allowing for thinner body panels that save about 30 kg (66 lb) from the vehicle's mass.
While most front-engine, rear-wheel-drive cars require two propeller shafts with a center bearing for rigidity, the short distance between the transmission and the differential gear made it possible to use only one - a carbon-composite shaft that saves an additional 3 kg (6.6 lb).
The RX-8's structure suppresses bending and twisting of the body and enhances performance by inhibiting vibration and minimizing noise. Suspension is by a double-wishbone configuration. The upper and lower arms in both front and rear are much longer than those in the RX-7 for better tire grip and cornering. Optimally set up roll center height and improved camber rigidity enhance control by reducing slower-handling reaction.
A freestyle door system with front- and rear-hinged doors and no center pillar makes getting into and out of the rear seats fast and easy.
- Patrick Ponticel
