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American Motors 290ci specs: 290 ci (4.8L) 8-cylinder, 3.75 x 3.28 in (95.3 x 83.3 mm) bore and stroke, 10:1 compression. Rated 225 hp, 1966–1969.
The American Motors 290ci is oversquare — the 3.75" bore exceeds the 3.28" stroke by 14.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.28" stroke does not reach 4,000 ft/min of mean piston speed until about 7,300 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.791 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 8 cylinders displaces 36.3 ci (594 cc).
10:1 is in the range that usually runs on pump premium.
It is one of 4 engines in the American Motors 290ci family, all of them 290 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated at 225 hp across 1966–1969.
| Displacement | 290 ci / 4.8 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.28" |
| Cylinders | 8 |
| Compression ratio | 10:1 |
| Rod length | 5.875" |
| Rod ratio | 1.791 |
| Bore/stroke ratio | 1.143 |
| Piston deck clearance | 0.02" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 225 hp |
| Years | 1966–1969 |
| Bore/stroke character | 1.143 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,280 ft/min — conservative for a street engine |
| Rod ratio | 1.791 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 36.3 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.787" |
|---|---|
| Exhaust valve diameter | 1.406" |
| Chamber volume | 52.93 cc |
| Rocker ratio | 1.6:1 |
| Lifter type | hydraulic |
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 |
|---|---|---|
| 1966 | 225 hp | — |
| 1967 | 225 hp | — |
| 1968 | 225 hp | — |
| 1969 | 225 hp | — |