Mazda Wankel engine 12A

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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.



File:Mazda HB Cosmo 007.JPG
Turbocharged 12A installed in Mazda Cosmo

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.Template:Citation needed In 1982 a 12A turbo powered Cosmo coupe was officially the fastest production car in JapanTemplate: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.


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