See other engines in this family
Mazda 12A specs: 1.146L (70 ci) 2-cylinder, 90 x 80 mm (3.5433 x 3.1496 in) bore and stroke. Rated 100 hp, 1979–1985. Used in the Mazda RX-7. Rotary.
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. 7 factory variants share these dimensions, rated at 100 hp across 1979–1985.
| Displacement | 70 ci / 1.146 L |
|---|---|
| Bore | 3.5433" |
| Stroke | 3.1496" |
| Cylinders | 2 |
| Bore/stroke ratio | 1.125 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | Rotary |
| Fuel type | gas |
| Advertised HP | 100 hp |
| Years | 1979–1985 |
| Bore/stroke character | 1.125 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,150 ft/min — conservative for a street engine |
| Displacement per cylinder | 35.0 ci |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 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 |