By Haruo Okimoto, Manager, and Seiji Tajima, Senior Staff Member
RE Engineering Group, Powertrain Development Division

The RX-8 is built to accommodate Mazda's RENESIS rotary engine, an ideal powerplant for sports cars. It is powerful, smooth, lightweight and compact, and it has a low center of gravity.

"RENESIS," derived from the word "genesis," suggests the beginning of a new type of rotary engine. Mazda's work on rotary engines began in 1961 and, six years later, we introduced the Cosmo Sport, powered by the world's two-rotor engine. Over the years, we made countless improvements. Today. The rotary engine is used in the turbocharged RX-7 that we sell in Japan. Through 2000, we have sold about 1.8 million cars rotary engine-powered cars.

The RENESIS is an advanced version of the MSP-RE concept rotary engine featured in the RX-01 concept sports car exhibited at the 1995 Tokyo Motor Show. This new-generation rotary engine was employed in the RX-EVOLV four-passenger sports car shown first at the 1999 Tokyo Motor Show.

When developing the RENESIS, we aimed to retain power output on a par with the turbocharged 13B-REW, the rotary engine that powers the RX-7, while offering improved fuel economy and reduced emissions.

Side Intake and Exhaust Ports

Unlike previous mass-production rotary engines, which employed side exhaust ports and peripheral intake ports, the naturally aspirated RENESIS has intake and exhaust ports in the side housings. This configuration eliminates overlap between the opening of the intake and exhaust ports, enhancing combustion efficiency. The intake ports are 30% larger and their timing has been changed to make them open sooner than in previous designs. Moreover, the exhaust ports open later, resulting in a longer power (expansion) stroke and providing radically improved heat efficiency.

At the same time, the RENESIS uses a six-port induction (6PI) design, in which each rotor employs three intake ports, and a variable intake timing mechanism. Under this system, dedicated high-speed intake ports begin to operate when the engine operates at high-rev levels. This makes it possible to use the intake's dynamic effect at high and low speeds to maximize compression efficiency.

Unlike the single peripheral port per rotor of previous designs, the RENESIS uses two exhaust ports per rotor. This produces a combined exhaust port opening area nearly twice as large and results in a substantial reduction in exhaust resistance.

The rotors have also been made lighter for better performance at high-rev levels. The rotors used in the RENESIS weigh approximately 14% less than those used in the engine that powers the RX-7, which we sell in Japan.

These enhancements provide high output rivaling the power of turbocharged rotary engines with linear power characteristics from the low- to the high-rev range.

Fuel Efficiency

The increased heat efficiency resulting from zero overlap between the opening of the intake and exhaust ports makes it possible for the RENESIS to run on a leaner fuel mixture than conventional rotary engines. When idling, the RENESIS consumes 40% less fuel than the current production rotary engine.

Reciprocating piston engines generally use a richer fuel mixture under high-speed and high-load conditions to prevent knocking. In contrast, rotary engines do not require a particularly rich fuel mixture under these conditions due to their special combustion characteristics. In addition, the RENESIS achieves nearly complete combustion over the entire speed range thanks to its high compression ratio and the use of new fuel injectors designed for improved fuel atomization. These enhancements allow the RENESIS to run on a leaner fuel mixture than conventional rotary engines from the low to the high-rev range. The result is the power and performance of a sports car engine and reduced fuel consumption. Low Emissions

Due to their configurations, rotary engines produce less nitroxide (NOx) than reciprocating piston engines, but they also tend to produce large amounts of unburned hydrocarbons. The side exhaust layout used in the RENESIS prevents unburned hydrocarbons of the combustion chamber housing from escaping to the exhaust ports.

Instead, they are carried over and burned in the next combustion cycle, dramatically reducing emissions. In addition, air injection directed into the combustion chamber increases the efficiency of the exhaust reaction, significantly over Mazda's existing system during engine startup. Together with the double-skin exhaust manifold, the new layout makes the exhaust much hotter when it reaches the catalytic converter, speeding the converter reaction for clean emissions from the moment the engine is started.

Low Center of Gravity

With their low center of gravity rotary engines have an advantage over reciprocating piston engines. We have exploited this benefit by using a special oil pan configuration to make the engine's center of gravity even lower.

Called the "wet sump" layout, it uses a baffle (dividing panel) within the oil pan to prevent oil from collecting on one side during cornering. This makes it possible to use a shallower oil pan. Mazda engineers also experimented with "dry sump" designs, but they settled on the new wet sump layout after considering weight, cost and the greater reliability of the simpler system. The new oil pan is only about 40 mm thick, about half the thickness of conventional designs.

Reduced Oil Consumption

In a rotary engine, oil is supplied directly to the interior walls of the combustion chamber to lubricate the "apex" and "corner" seals. We've kept the paths which supply oil in the RENESIS as small as possible, and we have redesigned the oil supply nozzles to improve their efficiency. With these enhancements, the RENESIS consumes about half as much oil as a conventional rotary engine.

Superb Response and Sound to Thrill the Senses

The RENESIS achieves a sophisticated balance between high revs and high output, on the one hand, and fuel economy and low emissions, on the other. In addition, we are working to enhance the performance and to realize the high degree of reliability and durability required in a mass-production sports car. We want to achieve output of 250 horsepower.

Unlike rotary engines equipped with peripheral exhaust ports, the side layout of the RENESIS produces clear, transparent high tones and powerful low tones. We recognize engine sound as a key element in any sports car, and we are working to ensure that the engine produces a satisfying roar as you depress the accelerator.

All of us on the rotary engine engineering team hope you will have the opportunity to experience the feeling that only the RENESIS can deliver. We are dedicated to delivering an engine that will delight sports car enthusiasts worldwide.