See other engines in this family
Plymouth LA 318 4-bbl specs: 318 ci (5.2L) 8-cylinder, 3.909 x 3.311 in (99.3 x 84.1 mm) bore and stroke. Rated 155-175 hp, 1978–1987.
The Plymouth LA 318 4-bbl 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. A rod ratio of 1.849 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 39.8 ci (651 cc).
It is one of 17 engines in the LA family, sitting between the 273 ci and 360 ci members. 9 factory variants share these dimensions, rated from 155 to 175 hp across 1978–1987.
| Displacement | 318 ci / 5.2 L |
|---|---|
| Bore | 3.9094" |
| Stroke | 3.311" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8–8.5:1 (published figures vary) |
| Rod length | 6.123" |
| Rod ratio | 1.849 |
| Bore/stroke ratio | 1.181 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Firing order | 1-8-4-3-6-5-7-2 |
| Advertised HP | 155–175 hp |
| Years | 1978–1987 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 1980 | E47 net | 155 @ 4000 | 240 lb-ft @ 2000 | — |
Factory specification sheet.
| 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 |
| Rod ratio | 1.849 — long — less side loading on the cylinder wall, favours high RPM |
| 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 |
|---|---|---|
| 1978 | 155 hp | LA 318 4-bbl |
| 1979 | 155 hp | LA 318 4-bbl |
| 1980 | 155 hp | LA 318 4-bbl |
| 1982 | 165 hp | LA 318 4-bbl |
| 1983 | 165 hp | LA 318 4-bbl |
| 1984 | 165 hp | LA 318 4-bbl |
| 1985 | 175 hp | LA 318 4-bbl |
| 1986 | 175 hp | LA 318 4-bbl |
| 1987 | 175 hp | LA 318 4-bbl |
8 factory vehicles, 1978–1989. Each year opens that model's engine table.