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Plymouth LA (1965–1980) specs: 318 ci (5.2L) 8-cylinder, 3.909 x 3.311 in (99.3 x 84.1 mm) bore and stroke. Rated 120-230 hp, 1965–1980.
The Plymouth LA (1965–1980) is oversquare — the 3.9094" bore exceeds the 3.311" stroke by 18.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.311" stroke does not reach 4,000 ft/min of mean piston speed until about 7,250 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 39.8 ci (651 cc).
It is one of 12 engines in the LA family, sitting between the 273 ci and 360 ci members. 20 factory variants share these dimensions, rated from 120 to 230 hp across 1965–1980.
| Displacement | 318 ci / 5.2 L |
|---|---|
| Bore | 3.9094" |
| Stroke | 3.311" |
| Cylinders | 8 |
| Configuration | V8 |
| Bore/stroke ratio | 1.181 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 120–230 hp |
| Years | 1965–1980 |
| Bore/stroke character | 1.181 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,311 ft/min — conservative for a street engine |
| Displacement per cylinder | 39.8 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 |
|---|---|---|
| 1965 | 230 hp | — |
| 1966 | 230 hp | — |
| 1967 | 230 hp | — |
| 1968 | 230 hp | — |
| 1969 | 230 hp | — |
| 1970 | 230 hp | — |
| 1971 | 230 hp | — |
| 1972 | 150 hp | — |
| 1973 | 150 hp | — |
| 1973 | 170 hp | — |
| 1974 | 150 hp | — |
| 1974 | 170 hp | — |
| 1975 | 145 hp | — |
| 1976 | 145 hp | — |
| 1976 | 150 hp | — |
| 1977 | 145 hp | — |
| 1978 | 140 hp | — |
| 1978 | 155 hp | — |
| 1979 | 135 hp | — |
| 1980 | 120 hp | — |