1970-1985 Mazda Rotary Engine 12A and Trans-PARTS ONLY

The 12A is an "elongated" version of the 10A: the rotor radius was the same, but the depth was increased by 10 mm (0.39 in) to 70 mm (2.8 in). It continued the two-rotor design; with the depth increase each chamber displaced 573 cc (35.0 cu in) so two chambers (one per rotor) would displace 1,146 cc (69.9 cu in); the series name continues earlier practice and reflects this value ("12" suggesting 1.2 litres). 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 favour 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 N?m (115 lbf?ft)
• 1972–1974 Mazda RX-3 (Japan), 110 hp (82 kW) and 135 N?m (100 lbf?ft)
• 1972–1974 Mazda RX-4
• 1972–1980 Mazda Luce
• 1978–1985 Mazda RX-7, 100 hp (75 kW)
• Aero Design DG-1 racing aircraft used two Mazda RX-3 (12A) engines, each driving a propeller—one at the front, the other at the rear of the aircraft.
• Lean-burn
  • 1979–1985 Mazda RX-7 (Japan)
  • 1980–1985 Mazda RX-7 (United States)
• 6PI
  • 1981–1985 Mazda Luce
  • 1981–1985 Mazda Cosmo