Hardcore rotary fans are passionate to say the least and some may say cultist in their obsession with all things Wankel, but comparing them to zombies may be a bit harsh. Rotorheads are a lively bunch with an appreciation of outside-the-box thinking and leading edge technology; what’s not to like?
The Mazda rotary engine is the ultimate underdog, belting out big league power numbers from a scant 80 inches of displacement. At 350 cubic inches, a small-block Chevy is more than four times bigger than a 13B. To put things in perspective, the 1993 Mazda RX-7’s 1.3-liter 13B pumps out 255 horsepower or 196 horsepower per liter. Conversely, the ’93 C4 Corvette flagship, the ZR-1, produced 405 horses from its 5.7-liter LT5 V8 or only 71 horsepower per liter.
It should also be noted that Mazda is celebrating the 20th anniversary of its overall victory at the legendary 24 Hours of Le Mans in 1991. Mazda is the only Japanese manufacturer to ever take overall victory at Circuit De La Sarthe, its weapon of choice was the Mazda 787B powered by a special four-rotor R26B rotary powerplant.
Rotors vs. Pistons
A rotary engine generates its power in a decidedly unique fashion. Engines are all about compressing air and burning fuel. Pistons in a conventional reciprocating internal combustion engine are moved up and down in a cylinder via connecting rods and a crankshaft. They operate in four cycles: intake, compression, ignition and exhaust with the piston’s movement creating the compression/combustion in the cylinder head at or near TDC.
Sometimes called a Wankel rotary in reference to its inventor, Dr. Felix Wankel, the rotary engine consists of two rotors, two rotor housings, three support housings (front, intermediate and rear side), stationary gears, an output shaft and bearings. Where a piston engine’s combustion chamber is fixed, the combustion chamber in a rotary powerplant spins around inside the engine.
“Rotary combustion chamber”
Understanding The Beast
The rotors consist of convex triangular components (familiar to most enthusiasts) with gear teeth at their center. Pockets that serve as combustion areas are carved on the outside edges of the rotor. The edges where the convex faces meet are fitted with apex seals that seal in the combustion chamber in much the same way a head gasket works in a piston engine.
Each rotor spins in a housing that has spark plug, intake and exhaust accommodations machined into it. The inside surface of the housing is an epitrochoid shape, an oval shape with a slight hourglass effect in the mid-section.
This unique shape allows the apex seals to maintain constant contact with the surface as the rotor spins on the output shaft ensuring uncompromised combustion.
As the rotor turns in the engine, the combustion pocket experiences the four cycles of combustion. The output shaft is the equivalent of a crankshaft in a piston design and its off-center (eccentric) lobes provide the leverage needed to spin the shaft, which generates torque that is sent to the drivetrain via a flywheel. The front, intermediate and rear side housings contain the gears and bearings to support and lubricate the output shaft.
Porting Gateway To Rotary Power
Porting the housing on a rotary engine is akin to cylinder head work on a piston engine. It addresses the amount of air moving through the engine, which ultimately provides the potential to burn more fuel and make more power. But there are compromises at work, as more aggressive porting can have unwanted effects on drivability and fuel efficiency among other things. Rotary builders use four different types of porting.
Street Port
A street or “mild” port cleans up the port but only slightly alters its shape. This porting job also adds a lip at the top of the port for enhanced flow. This method bumps top-end power without changing the engine’s operating characteristics.