R26B in 787B
On 23 June 1991 Mazda won the 24-hour Le Mans endurance race with a Category 2 (C2) 787B racer, #55, powered by a 4-rotor R26B--the first and likely last rotary win because of C2 rule changes prohibiting rotaries in 1992. Just to finish Le Mans is an accomplishment--let alone win. The 787B covered 4923.2 km (3059.1 mi) at an average speed of 205.3 kph (127.6 mph), exceeding 320 kph (200 mph) on the main straight. Yet it still had 30.0 liters (7.9 gallons) of fuel left of the maximum 2550 liters (673.6 gal) allotted, giving an impressive 4.6 mpg. Here's a look at this historic engine, emphasizing the DIFFERENCES between the R26B and the 13B whose geometry it's based on.
The R26B develops 700 net bhp (Japanese) at 9000 rpm, its redline, and 449 net lb-ft of torque at 6500 rpm. It's only 39" long and weighs just 396 lb. The R26B has a 3-piece eccentric shaft; the long main shaft has journals for rotors #2 and #3 and tapered extensions for 2 hollow shafts with journals for rotors #1 and #4. Counterweights are used at both ends. To stiffen the engine, aluminum honeycomb is used where needed, including the aluminum oil pan, which is mounted on top. The R26B uses a dry-sump oil system. Tension bolts are anchored throughout the intermediate housings, further increasing stiffness. Engine coolant and oil enter through the center housing.
Rotor and side housings are coated with hot-sprayed chrome-carbide cermet (ceramic in a metallic array) for high-temperature wear resistance. The intake as well as exhaust ports are peripheral. Each rotor housing has 3 spark plugs: a third "far-trailing" plug was added for better fuel economy and power. Rotors were precision cast to a 10.0:1 compression ratio using the lost-wax method to reduce rotating mass. Two-piece silicon nitride ceramic apex seals have, in the words of one summary, "a 'sprinkle' of an ingredient that raises heat conductivity", and they use 2 springs. The R26B has a sophisticated electronic port fuel injection system and telescopically variable intake pipes whose length vary with engine speed to improve airflow.
After winning, this historic engine was taken apart in front of the press. Little performance deterioration had been noted during the grueling race, and the R26B looked nearly new after dismantling. Even Mazda's head office engineer said, "In the case of the rotary engine, damage to the apex seal is the best reference. And as you can see, it's nearly untouched." After measurement, wear on apex seals, rubbing surfaces, and bearings were found to be only 1/3 to 1/2 the upper limits--in Mazda's words, "indicating remarkable durability and reliability". As racer Paul Frere was to say of the win, "A pity Felix Wankel has not lived to see it."