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Plymouth N specs: 383 ci (6.3L) 8-cylinder, 4.25 x 3.375 in (108 x 85.7 mm) bore and stroke. Rated 300-335 hp, 1970–1971. Used in the Dodge Challenger. OHV.
The Plymouth B (N) is oversquare — the 4.25" bore exceeds the 3.375" stroke by 25.9% — a layout that favors airflow and RPM over leverage at the crank. The 3.375" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 47.9 ci (785 cc).
It is one of 27 engines in the B family, sitting between the 350 ci and 400 ci members. 3 factory variants share these dimensions, rated from 300 to 335 hp across 1970–1971.
| Displacement | 383 ci / 6.3 L |
|---|---|
| Bore | 4.25" |
| Stroke | 3.375" |
| Cylinders | 8 |
| Configuration | V8 |
| Bore/stroke ratio | 1.259 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 300–335 hp |
| Years | 1970–1971 |
| Bore/stroke character | 1.259 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,375 ft/min — conservative for a street engine |
| Displacement per cylinder | 47.9 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 |
|---|---|---|
| 1970 | 330 hp | N |
| 1970 | 335 hp | N |
| 1971 | 300 hp | N |