The Mazda Wankel engines (a type of rotary combustion engine) are family of car engines derived from experiments in the early 1960s by Felix Wankel, a German engineer. Over the years, displacement has been increased and turbocharging has been added.
Wankel engines can be classified by their geometric size in terms of radius (rotor center to tip distance, also the median stator radius) and depth (rotor thickness), and offset (crank throw, eccentricity, also 1/4 the difference between stator's major and minor axes). These metrics function similarly to the bore and stroke measurements of a piston engine. Displacement is 3√3radius·offset·depth, multiplied with the number of rotors (note that this only counts a single face of each rotor as the entire rotor's displacement). Nearly all Mazda production Wankel engines share a single rotor radius, 105 mm (4.1 in), with a 15 mm (0.6 in) crankshaft offset. The only engine to diverge from this formula was the rare 13A, which used a 120 mm (4.7 in) rotor radius and 17.5 mm (0.7 in) crankshaft offset.
Mazda rotary engines have a reputation for being relatively small and powerful at the expense of poor fuel efficiency. They are starting to become popular with kit car builders, hot rodders and in light aircraft because of their light weight, compact size, and tuning potential stemming from their inherently high power to weight ratio[citation needed].
In auto racing, the displacement of a Wankel engine is usually doubled for classing purposes. For calculating taxes in Japan, the displacement of Wankel engines is defined as the equivalent of 1.5 times the nominal displacement, so the 1300 cc 13B engines are taxed as 1950 cc.
When Wankel engines became commonplace in motor sport events, this created the problem of accurate representation of each engine's displacement, for the benefit of competition. Rather than force the majority of participants (driving piston engine cars) to half their quoted displacement (likely resulting in confusion), most racing organizations simply decided to double the quoted displacement of Wankel engines.
In Le Mans racing, the first three-rotor engine used in the 757 was named the 13G.
The main difference between the 13G and 20B is that the 13G uses a factory peripheral intake port (used for racing) and the 20B (Three Rotor Engine) uses side intake ports.
It was renamed 20B after Mazda's naming convention for the 767 in November 1987.
The three-rotor 20B-REW was only used in the 1990-1995 Eunos Cosmo. It was the world's first volume production twin-turbo setup featured in both 13B-REW & 20B-REW form. It displaced 1962 cc (three 654 cc rotors) and used 0.7-bar (70 kPa) of turbo pressure to produce 300 horsepower (224 kW) and 407 newton metres (300 ft·lbf).
