It is through the severity of racing in events such as these that the current generation rotary engine has evolved.

The twin turbo 13B engine in the series VII version RX-7 was then improved yet again. With power output now standing at 194 kW, it gave unprecedented performance coupled with the ultra smooth power delivery that makes the rotary engine legendary. Mazda wouldn't have it any other way.

Today's Rotary Engine

A lot has changed through the years of development. As fitted to the 1974 RX-4, the carbureted 13B produced 95Kw @6500 rpm and 174 Nm of torque @4000 rpm. Later versions employed a unique sequential twin turbo system to produce 176 Kw at 6500 rpm and 300 Nm of torque @ 5000 rpm. Torque output was increased throughout the rev range with as much as 255Nm available at a low 2000 rpm. Maximum RPM was been raised to 8000 and the rotor's compression ratio of 9.0:1 necessitated premium grade unleaded petrol.

The engine inherited the basic 13B geometry and epitrochoidal dimensions of 654 cc for each of its two rotors. However in 13B REW configuration, many of the rotary's major mechanical and electronic systems received extensive modification. Among the many internal upgrades were a thin wall cast-iron rotor with fully machined combustion recesses to ensure uniform combustion. Apex seal slots were hardened to resist wear. Modifications have also been made to the aluminium rotor housing around the "hot spot" spark plug area for more coolant flow. The engine's induction, exhaust, cooling and lubrication were modified or redesigned when compared to the series V RX-7 engine.

Cooling and lubrication are vitally important to an engine producing the power the 13B REW. Both rotors are kept cool by splashing them internally with oil. Internal lubrication is via an electronically controlled metering system that reduces oil consumption by 25-50 per cent compared to the previous method of supply to the intake and trochoid chamber combined.

Lubrication is fed under high pressure to the eccentric shaft bearings via a high-efficiency multi port rotary pump. The heated oil is then sent through two oil-coolers (one in each of the nose vents ) before being re-used. A lightweight aluminium and plastic radiator, fully shrouded and slanted sharply to lower the RX-7's nose was fitted up front. Maintaining the correct temperature is a pair of three stage thermo fans and keeping the flow is a lightweight aluminium water pump.

The fire in the new 13B REW was supplied by the world's first volume-production sequential twin turbocharger system. It produced more power than a conventional twin turbo setup where both turbos boost at once, and suffered far less turbo lag. The advantage of the sequential system was the ability to utilise a small and large turbo at the same time. At low rpm the 51mm diameter turbo with its "impact" blade design spools very quickly, providing boost from as low as 1500 rpm. At a calculated point the second 57mm diameter turbo is switched on, giving full boost all the way to the 8000 rpm redline.

Mazda solved this problem by spooling the second turbo to a pre-boost speed of around 100,000 rpm with exhaust gas circulation. When the time comes for the second turbo to cut in, a by-pass valve is shut to "surge" the compressor, spinning it to over 140,000 rpm. This then assures a smooth coupling with the primary turbo. Once at the required speed, it receives a full share of exhaust flow to add its boost with the primary turbo.

The twin turbo chargers are fitted to a "dynamic pressure" cast iron exhaust manifold shaped to minimise the gap between the exhaust ports and the intake of the turbos, improving boost by as much as 35 per cent. The 13B-REW was fitted standard with an air-to-air intercooler mounted above the radiator with separate ducting.

The ECU controlled fuel injection system uses air density measurement instead of the common air flow metering to allow a smoother air flow and more precise fuel management. Coupled with the precise shape of the plenum chamber and inlet tract length, the added benefit of the increased power and throttle response is the additional improvement in fuel consumption for the city/highway cycle.

Two injectors per rotor look after the varied engine loads. The primary injector takes fuel from the side of the injector body instead of the top. The resulting reduction in fuel travel through the injector body gives a quicker and more precise engine re-start after high speed/load applications. The secondary injector is mounted upstream of the inlet tract operating during mid and high rpm. Change over to twin injector operation takes place around 2,750 rpm or lower if the load commands it.

Ignition timing of the four platinum tipped spark plugs (two per rotor) is controlled via the ECU which will automatically retard timing if detonation is detected. Light weight high energy coils are utilised to take advantage of the rotary's unique combustion characteristics.

Ensuring the emissions are lower than required, the use of a two stage catalyst system were the main three way converter gives the lowest flow resistance available. A single muffler is used for noise reduction and the whole system weighs considerably less compared to the series V RX-7.

RENESIS - The Future of the Rotary Engine

Both the Evolv and the RX-8 had many things in common, not the least of which was the latest version of the rotary engine called "RENESIS."

The RX-8 with its RENESIS rotary engine made its debut on Australian roads in August 2003.

The naturally-aspirated engine revs eagerly to extremely high engine speeds while producing racecar-like power and performance. "RENESIS" stands for "The RE (Rotary Engine)'s GENESIS", or the rotary engine for the new millennium.

The RENESIS engine is improved from the 13B rotary engine used in the RX-7. Refinements include positioning the exhaust and intake ports on the side housing, separate from the rotor housing. This reduces overlap between the opening of the intake and exhaust ports, stabilizing combustion. At the same time, it enables the intake port to be enlarged, increasing engine rotational speeds and power output to levels never-before achieved with a naturally aspirated production rotary engine. Other refinements, including thinner, lightweight rotors, thicker eccentric shaft, and a three-port, three-stage variable intake system, contribute to the engine's maximum power output of 177kW at 8,200 rpm, maximum torque of 211Nm at 5,500 rpm and a 10,000 rpm redline for the 6 speed manual and a maximum power output of 141kW at 7,000 rpm, maximum torque of 220Nm at.5,000 rpm for the activematic.

A new, compact wet-sump oil lubrication system, making use of the unique layout of the output shaft, and a thin oil pan contribute to the engine's lightweight compact design, which allows the engine to be located lower and further to the rear than ever before. For rotary engine enthusiasts, the next exciting phase in the great engine's history has already begun.