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Plymouth Slant-6 (1961–1980) specs: 225 ci (3.7L) 6-cylinder, 3.402 x 4.13 in (86.4 x 104.9 mm) bore and stroke. Rated 90-145 hp, 1961–1980.
The Plymouth Slant-6 (1961–1980) is undersquare — the 4.1299" stroke exceeds the 3.4016" bore by 17.6% — a layout that trades peak RPM for leverage and torque low in the range. The 4.1299" stroke puts mean piston speed at 4,000 ft/min around 5,800 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 37.5 ci (615 cc).
It is one of 7 engines in the Slant-6 family, the largest at 225 ci. 18 factory variants share these dimensions, rated from 90 to 145 hp across 1961–1980.
| Displacement | 225 ci / 3.7 L |
|---|---|
| Bore | 3.4016" |
| Stroke | 4.1299" |
| Cylinders | 6 |
| Bore/stroke ratio | 0.824 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 90–145 hp |
| Years | 1961–1980 |
| Bore/stroke character | 0.824 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,130 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 37.5 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 |
|---|---|---|
| 1961 | 145 hp | — |
| 1962 | 145 hp | — |
| 1963 | 145 hp | — |
| 1964 | 145 hp | — |
| 1965 | 145 hp | — |
| 1966 | 145 hp | — |
| 1967 | 145 hp | — |
| 1968 | 145 hp | — |
| 1969 | 145 hp | — |
| 1970 | 145 hp | — |
| 1971 | 145 hp | — |
| 1972 | 110 hp | — |
| 1973 | 105 hp | — |
| 1974 | 105 hp | — |
| 1975 | 95 hp | — |
| 1976 | 100 hp | — |
| 1979 | 100 hp | — |
| 1980 | 90 hp | — |