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Shelby 289ci specs: 4.7L (289 ci) 8-cylinder, 101.6 x 72.9 mm (4.0000 x 2.8700 in) bore and stroke, 12.7:1 compression. Rated 306 hp, 1966.
The Shelby 289ci is oversquare — the 4" bore exceeds the 2.87" stroke by 39.4% — a layout that favors airflow and RPM over leverage at the crank. The 2.87" stroke does not reach 4,000 ft/min of mean piston speed until about 8,350 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.796 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 36.1 ci (592 cc).
12.7:1 is high for a production gasoline engine; running a ratio like that on pump fuel depends on chamber design and fuel delivery rather than the number alone.
It is one of 4 engines in the Shelby 289ci family, all of them 289 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 289 ci / 4.7 L |
|---|---|
| Bore | 4" |
| Stroke | 2.87" |
| Cylinders | 8 |
| Compression ratio | 12.7:1 |
| Rod length | 5.155" |
| Rod ratio | 1.796 |
| Bore/stroke ratio | 1.394 |
| Piston deck clearance | 0.0015" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 306 hp |
| Years | 1966 |
| Bore/stroke character | 1.394 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,870 ft/min — conservative for a street engine |
| Rod ratio | 1.796 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 36.1 ci |
| Static compression | 12.7:1 — high enough that pump premium or better is normally required |
| Intake valve diameter | 1.875" |
|---|---|
| Exhaust valve diameter | 1.605" |
| Chamber volume | 42 cc |
| Rocker ratio | 1.6:1 |
| Lifter type | mechanical |
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