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Plymouth A12 specs: 440 ci (7.2L) 8-cylinder, 4.319 x 3.752 in (109.7 x 95.3 mm) bore and stroke. Rated 390 hp, 1969. Used in the Dodge Coronet. OHV.
The Plymouth RB (A12) 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. Each of the 8 cylinders displaces 55.0 ci (901 cc).
It is one of 25 engines in the RB family, the largest at 440 ci.
| Displacement | 440 ci / 7.2 L |
|---|---|
| Bore | 4.3189" |
| Stroke | 3.752" |
| Cylinders | 8 |
| Configuration | V8 |
| Bore/stroke ratio | 1.151 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 390 hp |
| Years | 1969 |
| 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 |
| Displacement per cylinder | 55.0 ci |
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