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Buick 300ci specs: 300 ci (4.9L) 8-cylinder, 3.75 x 3.40 in (95.3 x 86.4 mm) bore and stroke, 11:1 compression. Rated 250 hp, 1964. Used in the Buick Skylark.
The Buick 300ci is oversquare — the 3.75" bore exceeds the 3.4" stroke by 10.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.4" stroke does not reach 4,000 ft/min of mean piston speed until about 7,050 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.754 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 37.5 ci (615 cc).
11:1 is high enough that pump premium or better is normally required.
It is one of 3 engines in the Buick 300ci family, all of them 300 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 300 ci / 4.9 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.4" |
| Cylinders | 8 |
| Compression ratio | 11:1 |
| Rod length | 5.963" |
| Rod ratio | 1.754 |
| Bore/stroke ratio | 1.103 |
| Piston deck clearance | 0.036" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 250 hp |
| Years | 1964 |
| Bore/stroke character | 1.103 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,400 ft/min — conservative for a street engine |
| Rod ratio | 1.754 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 37.5 ci |
| Static compression | 11:1 — high enough that pump premium or better is normally required |
| Intake valve diameter | 1.625" |
|---|---|
| Exhaust valve diameter | 1.313" |
| Chamber volume | 50.14 cc |
| Rocker ratio | 1.6:1 |
| Lifter type | hydraulic |
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