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
The 12A is an "elongated" version of the 10A — the rotor radius was the same, but the depth was increased by 10 mm (0.4 in) to 70 mm (2.8 in). Each of its two rotors displaced 573 cc for a total of 1146 cc. The 12A series was produced for 15 years, from May 1970 through 1985. In 1974, a 12A became the first engine built outside of western Europe or the U.S to finish the 24 hours of Le Mans.
In 1974, a new process was used to harden the rotor housing. The Sheet-metal Insert Process (SIP) used a sheet of steel much like a conventional piston engine cylinder liner with a chrome plated surface. The side housing coating was also changed to eliminate the troublesome sprayed metal. The new "REST" process created such a strong housing, the old carbon seals could be abandoned in favor of conventional cast iron.
Early 12A engines also feature a thermal reactor, similar to the 0866 10A, and some use an exhaust port insert to reduce exhaust noise. A lean-burn version was introduced in 1979 (in Japan) and 1980 (in America) which substituted a more-conventional catalytic converter for this "afterburner". A major modification of the 12A architecture was the 6PI which featured variable induction ports.
Applications:
1970–1972 Mazda R100
1970–1974 Mazda RX-2, 130 hp (97 kW) and 156 Nm (115 ft·lbf)
1972–1974 Mazda RX-3 (Japan), 110 hp (82 kW) and 135 Nm (100 ft·lbf)
1972–1974 Mazda RX-4
1972–1980 Mazda Luce
1978–1979 Mazda RX-7, 100 hp (75 kW)
Lean-burn
1979–1985 Mazda RX-7 (Japan)
1980–1985 Mazda RX-7 (USA)
6PI
1981–1985 Mazda Luce
1981–1985 Mazda Cosmo
Turbo
The ultimate 12A engine was the turbocharged and fuel injected engine used in the Japan-spec HB series Cosmo, Luce, and SA series RX-7.[citation needed] In 1982 a 12A turbo powered Cosmo coupe was officially the fastest production car in Japan[citation needed]. It featured "semi-direct injection" into both rotors at once, a technique that was much more successful than it would appear. A passive knock sensor was used to eliminate knocking, and later models featured a specially-designed "Impact Turbo" which was tweaked for the unique exhaust signature of the Wankel engine for a 5 horsepower increase. The engine continued until 1989 in the HB Cosmo series but by that stage it had grown a reputation as a thirsty engine.
Output of the Impact Turbo version was 165 hp (123 kW) at 6000 rpm and 231 Nm (170 ft·lbf) at 4000 rpm.
Applications:
1982–1989 Mazda Cosmo
1982–1985 Mazda Luce
1984–1985 Mazda RX-7
