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Pontiac 230ci specs: 230 ci (3.8L) 6-cylinder, 3.875 x 3.25 in (98.4 x 82.6 mm) bore and stroke, 10.5:1 compression. Rated 207 hp, 1966.
The Pontiac 230ci is oversquare — the 3.875" bore exceeds the 3.25" stroke by 19.2% — 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 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 6 cylinders displaces 38.3 ci (628 cc).
10.5:1 is in the range that usually runs on pump premium.
It is one of 4 engines in the Pontiac 230ci family, all of them 230 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 230 ci / 3.8 L |
|---|---|
| Bore | 3.875" |
| Stroke | 3.25" |
| Cylinders | 6 |
| Compression ratio | 10.5:1 |
| Rod length | 5.7" |
| Rod ratio | 1.754 |
| Bore/stroke ratio | 1.192 |
| Piston deck clearance | 0.0145" |
| Advertised HP | 207 hp |
|---|---|
| Years | 1966 |
| Bore/stroke character | 1.192 — 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 | 1.754 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 38.3 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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