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Ram LA 3.9 specs: 239 ci (3.9L) 6-cylinder, 3.909 x 3.311 in (99.3 x 84.1 mm) bore and stroke. Rated 125 hp, 1987–1991. Used in the Dodge Dakota. OHV.
The Ram LA 3.9 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 6 cylinders displaces 39.8 ci (653 cc).
It is one of 13 engines in the Magnum family, sitting between the 226 ci and 488 ci members. 5 factory variants share these dimensions, rated at 125 hp across 1987–1991.
| Displacement | 239 ci / 3.9 L |
|---|---|
| Bore | 3.9094" |
| Stroke | 3.311" |
| Cylinders | 6 |
| Configuration | V6 |
| Bore/stroke ratio | 1.181 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 125 hp |
| Years | 1987–1991 |
| 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 |
|---|---|---|
| 1987 | 125 hp | LA 3.9 |
| 1988 | 125 hp | LA 3.9 |
| 1989 | 125 hp | LA 3.9 |
| 1990 | 125 hp | LA 3.9 |
| 1991 | 125 hp | LA 3.9 |