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Oldsmobile 324ci specs: 324 ci (5.3L) 8-cylinder, 3.875 x 3.438 in (98.4 x 87.3 mm) bore and stroke, 8.5:1 compression. Rated 185-202 hp, 1955.
The Oldsmobile 324ci is oversquare — the 3.875" bore exceeds the 3.438" stroke by 12.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.438" stroke puts mean piston speed at 4,000 ft/min around 7,000 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.927 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 40.5 ci (664 cc).
8.5:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Oldsmobile 324ci family, all of them 324 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated from 185 to 202 hp in 1955.
| Displacement | 324 ci / 5.3 L |
|---|---|
| Bore | 3.875" |
| Stroke | 3.438" |
| Cylinders | 8 |
| Compression ratio | 8.5:1 |
| Rod length | 6.625" |
| Rod ratio | 1.927 |
| Bore/stroke ratio | 1.127 |
| Induction | 1-2 |
|---|---|
| Advertised HP | 185–202 hp |
| Years | 1955 |
| Bore/stroke character | 1.127 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,438 ft/min — conservative for a street engine |
| Rod ratio | 1.927 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 40.5 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
| Chamber volume | 88.48 cc |
|---|---|
| Rocker ratio | 1.8:1 |
| 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 | 185 hp | — |
| 1955 | 202 hp | — |