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Pontiac 287ci specs: 287 ci (4.7L) 8-cylinder, 3.75 x 3.25 in (95.3 x 82.6 mm) bore and stroke, 8:1 compression. Rated 180-200 hp, 1955.
The Pontiac 287ci is oversquare — the 3.75" bore exceeds the 3.25" stroke by 15.4% — a layout that favors airflow and RPM over leverage at the crank. The 3.25" stroke does not reach 4,000 ft/min of mean piston speed until about 7,400 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 2.038 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 35.9 ci (588 cc).
8:1 is low by modern standards and generally happy on regular pump fuel.
2 factory variants share these dimensions, rated from 180 to 200 hp in 1955.
| Displacement | 287 ci / 4.7 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.25" |
| Cylinders | 8 |
| Compression ratio | 8:1 |
| Rod length | 6.625" |
| Rod ratio | 2.038 |
| Bore/stroke ratio | 1.154 |
| Piston deck clearance | 0" |
| Induction | 1-2 |
|---|---|
| Advertised HP | 180–200 hp |
| Years | 1955 |
| Bore/stroke character | 1.154 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,250 ft/min — conservative for a street engine |
| Rod ratio | 2.038 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 35.9 ci |
| Static compression | 8:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.78" |
|---|---|
| Exhaust valve diameter | 1.5" |
| Chamber volume | 73 cc |
| Rocker ratio | 1.5:1 |
| Lifter type | hydraulic |
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These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1955 | 180 hp | — |
| 1955 | 200 hp | — |