See other engines in this family
Plymouth A specs: 273 ci (4.5L) 8-cylinder, 3.63 x 3.311 in (92.2 x 84.1 mm) bore and stroke, 10.5:1 compression. Rated 235 hp. Rod ratio and piston speed.
The Plymouth LA (A) is oversquare — the 3.6299" bore exceeds the 3.311" stroke by 9.6% — 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 34.1 ci (559 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, the smallest at 273 ci. 2 factory variants share these dimensions, rated at 235 hp. Factory fitments include the Plymouth Barracuda Formula S, Plymouth Valiant Signet, Plymouth Barracuda and 1 other.
| Displacement | 273 ci / 4.5 L |
|---|---|
| Bore | 3.6299" |
| Stroke | 3.311" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 1.096 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 235 hp |
| Bore/stroke character | 1.096 — 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 | 34.1 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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 |
|---|---|---|
| — | 235 hp | A |
| — | 235 hp | A |