12A
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Written by Wesley Mahler   
04.11.2006

The 12A Series

Rotary Engine History

The 12A series motor was in production for about 15 years, from 1970 through 1985.  During 1974 the 12A became one of the first engines outside the US or Europe to compete and finish in the famous 24 hours of Le Mans The 12A is considered a “bored-out” version of the previous 10A engine.  Although the diameter of the rotors stayed the same, the depth was increased by 10mm (0.4 in) to 70 mm (2.8 in).  Each rotor housing had a displacement of 573 cc, combined the engine had a total of 1146 cc.

During the production of the 12A engine they started using a new method of hardening the rotor housings.  In 1974 the Sheet-metal Insert Process (SIP) would use a sheet of steel similar to a piston engine’s cylinder liner with a chrome plated surface.  They also changed the side housing coating which eliminated the problematic sprayed metal that was used previously.  

W
12A
Production: 1970 - 1985
Rotors: 2x573 cc
Power: 100 hp (75 kW)
Torque: _
Applications: 1970 - 1972 R100
1970 - 1974 RX-2
1972 - 1974 RX-3
1972 - 1974 RX-4
1972 - 1986 Luce
1978 - 1979 RX-7
12A Lean-Burn
Production: 1979 - 1985
Rotors: 2x573 cc
Power: _
Torque: _
Applications: 1979 - 1985 RX-7
12A-6PI
Production: 1981 - 1985
Rotors: 2x573 cc
Power: _
Torque: _
Applications: 1981 - 1985 RX-7
12A-Turbo
Production: 1983 - 1985
Rotors: 2x573 cc
Power: 132 hp (98 kW)
Torque: 137 ft.lbf (186 Nm)
Applications: 1983 - 1985 Cosmo
1983 - 1985 Luce
1984 - 1985 RX-7
ith the use of the new “REST” process, they were able to create a significantly strong housing.  This would make it possible to start using conventional cast iron instead of the old carbon seals.  The earlier 12A motors featured a thermal reactor, which were similar to the 0866 10A.  Some used an exhaust port insert which reduced exhaust noise. 

A later lean-burn model was created in Japan on 1979 and in America on 1980 which substituted a more-conventional catalytic converter for this “afterburner.”  Another significant change in the 12A setup was the use of the six port inserts, (6PI) which featured variable induction ports.

Applications:
  • 1970–1972 Mazda R100
  • 1970–1974 Mazda RX-2, 130 hp (97 kW) and 115 ft/lbf (156 Nm)
  • 1972–1974 Mazda RX-3 ( Japan ), 110 hp (82 kW) and 100 ft/lbf (135 Nm)
  • 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 - 985 Mazda Cosmo

12A Turbo

The fastest 12A motor produced was the turbocharged and fuel injected model.  This was used in the Japan-spec Mazda Luce, Cosmo and the RX-7. Luce, RX-7, and the Cosmo.  This engine showcased a “semi-direct injection” into both rotors at once, this technique turned out to be more successful than it appeared.  They added a passive knock sensor to eliminate engine detonation, and some later models included a specially designed “impact turbo,” which was tweaked to give the rotary engine a unique exhaust sound.  This motor produced 165 hp (123 kW) at 6000 RPM and 186 Nm (137 ft/lbf) at 4000 RPM.

Applications:
  • 1982–1985 Mazda Cosmo
  • 1982–1985 Mazda Luce
  • 1984–1985 Mazda RX-7

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Last Updated ( 04.11.2006 )
 
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