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American Motors 121ci (1977–1979) specs: 121 ci (2.0L) 4-cylinder, 3.405 x 3.323 in (86.5 x 84.4 mm) bore and stroke, 8.1:1 compression. Built 1977–1979.
The American Motors 121ci (1977–1979) is close to square: 3.4055" bore against 3.3228" stroke, within 2.5%, which splits the difference between a high-revving layout and a torque layout. The 3.3228" stroke does not reach 4,000 ft/min of mean piston speed until about 7,200 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 30.3 ci (496 cc).
8.1:1 is low by modern standards and generally happy on regular pump fuel.
3 factory variants share these dimensions across 1977–1979.
| Displacement | 121 ci / 2 L |
|---|---|
| Bore | 3.4055" |
| Stroke | 3.3228" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 8.1:1 |
| Bore/stroke ratio | 1.025 |
| Fuel type | gas |
|---|---|
| Years | 1977–1979 |
| Bore/stroke character | 1.025 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,323 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.3 ci |
| Static compression | 8.1:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| 1977 | — | — |
| 1978 | — | — |
| 1979 | — | — |
2 factory vehicles, 1977–1979. Each year opens that model's engine table.