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Plymouth RB (1966–1978) specs: 440 ci (7.2L) 8-cylinder, 4.319 x 3.752 in (109.7 x 95.3 mm) bore and stroke. Rated 255-390 hp, 1966–1978.
The Plymouth RB (1966–1978) is oversquare — the 4.3189" bore exceeds the 3.752" stroke by 15.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.752" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.804 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 55.0 ci (901 cc).
It is one of 16 engines in the RB family, the largest at 440 ci. 23 factory variants share these dimensions, rated from 255 to 390 hp across 1966–1978.
| Displacement | 440 ci / 7.2 L |
|---|---|
| Bore | 4.3189" |
| Stroke | 3.752" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 8.2–10.3:1 (published figures vary) |
| Rod length | 6.768" |
| Rod ratio | 1.804 |
| Bore/stroke ratio | 1.151 |
| 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 | 255–390 hp |
| Years | 1966–1978 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. | Duration int / exh | Valve lift int / exh | LSA |
|---|---|---|---|---|---|---|---|
| 1967 | gross | 350 @ 4400 | 480 lb-ft @ 2500 | 10.1:1 | — | — | — |
| 1967 | gross | 375 @ 4600 | 480 lb-ft @ 3200 | 10.1:1 | — | — | — |
| 1968 | gross | 350 @ 4400 | 480 lb-ft @ 2500 | 10.1:1 | 256° / 260° | 0.425" / 0.435" | 113° |
| 1968 | gross | 375 @ 4600 | 480 lb-ft @ 3200 | 10.1:1 | 268° / 284° | 0.450" / 0.458" | 115° |
| 1969 | gross | 350 @ 4400 | 480 lb-ft @ 2800 | 10.1:1 | — | — | — |
| 1969 | gross | 375 @ 4600 | 480 lb-ft @ 3200 | 10.1:1 | 268° / 284° | 0.450" / 0.465" | 115° |
| 1970 | gross | 350 | — | — | 256° / 260° | 0.425" / 0.435" | 113° |
| 1970 | gross | 375 @ 4600 | — | — | 268° / 284° | 0.450" / 0.458" | 115° |
| 1971 | gross | 335 @ 4400 | 460 lb-ft @ 3200 | 8.8:1 | — | — | — |
| 1971 | gross | 370 @ 4600 | 480 lb-ft @ 3200 | 9.5:1 | — | — | — |
| 1971 | gross | 385 @ 4700 | 490 lb-ft @ 3200 | 10.3:1 | — | — | — |
| 1972 | net | 280 @ 4800 | 375 lb-ft @ 3200 | 8.2:1 | 268° / 284° | 0.450" / 0.464" | 115° |
Factory specification sheet. Durations are the factory's advertised figures at the basis printed on the sheet, not duration at .050" lift; lobe separation is calculated from the printed valve timing.
| Bore/stroke character | 1.151 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,752 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.804 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 55.0 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 |
|---|---|---|
| 1966 | 365 hp | — |
| 1967 | 350 hp | — |
| 1967 | 375 hp | — |
| 1968 | 350 hp | — |
| 1968 | 375 hp | — |
| 1969 | 350 hp | — |
| 1969 | 375 hp | — |
| 1970 | 350 hp | — |
| 1970 | 375 hp | — |
| 1970 | 390 hp | — |
| 1971 | 335 hp | — |
| 1971 | 370 hp | — |
| 1971 | 385 hp | — |
| 1972 | — | — |
| 1972 | 280 hp | — |
| 1973 | — | — |
| 1973 | 280 hp | — |
| 1974 | — | — |
| 1974 | 275 hp | — |
| 1975 | — | — |
| 1976 | 255 hp | — |
| 1977 | — | — |
| 1978 | 255 hp | — |
4 factory vehicles, 1966–1978. Each year opens that model's engine table.