See other engines in this family
Mazda 12A specs: 1.146L (70 ci) 2-cylinder. Rated 90-100 hp, 1971–1985. Used in the Mazda RX-2 and Mazda RX-3. Rotary. Rod ratio and piston speed worked out.
The Mazda Rotary (12A) is oversquare — the 3.5433" bore exceeds the 3.1496" stroke by 12.5% — a layout that favors airflow and RPM over leverage at the crank. The 3.1496" stroke does not reach 4,000 ft/min of mean piston speed until about 7,600 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 2 cylinders displaces 35.0 ci (574 cc).
It is one of 16 engines in the Rotary family, sitting between the 59.9 ci and 119.7 ci members. 18 factory variants share these dimensions, rated from 90 to 100 hp across 1971–1985.
| Displacement | 70 ci / 1.146 L |
|---|---|
| Cylinders | 2 |
| Bore/stroke ratio | 1.125 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | Rotary |
| Fuel type | gas |
| Advertised HP | 90–100 hp |
| Years | 1971–1985 |
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1971 | — | 12A |
| 1972 | — | 12A |
| 1972 | 90 hp | 12A |
| 1973 | — | 12A |
| 1973 | 90 hp | 12A |
| 1974 | — | 12A |
| 1974 | 90 hp | 12A |
| 1975 | 90 hp | 12A |
| 1976 | 95 hp | 12A |
| 1977 | 95 hp | 12A |
| 1978 | — | 12A |
| 1979 | 100 hp | 12A |
| 1980 | 100 hp | 12A |
| 1981 | 100 hp | 12A |
| 1982 | 100 hp | 12A |
| 1983 | 100 hp | 12A |
| 1984 | 100 hp | 12A |
| 1985 | 100 hp | 12A |
3 factory vehicles, 1971–1985. Each year opens that model's engine table.