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Plymouth 340 LA V8 specs: 340 ci (5.6L) 8-cylinder, 4.039 x 3.311 in (102.6 x 84.1 mm) bore and stroke, 10.5:1 compression. Rated 275 hp. OHV.
The Plymouth 340 LA V8 is oversquare — the 4.0394" bore exceeds the 3.311" stroke by 22.0% — 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 8 cylinders displaces 42.5 ci (696 cc).
10.5:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 20 engines in the LA family, sitting between the 273 ci and 360 ci members. Factory fitments include the AAR Cuda, Duster 340, Road Runner and 6 others.
| Displacement | 340 ci / 5.6 L |
|---|---|
| Bore | 4.0394" |
| Stroke | 3.311" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 1.22 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 275 hp |
| Bore/stroke character | 1.220 — 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 | 42.5 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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