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Pontiac 250ci (1968–1971) specs: 250 ci (4.1L) 6-cylinder, 3.877 x 3.535 in (98.5 x 89.8 mm) bore and stroke. Rated 145-155 hp, 1968–1971.
The Pontiac 250ci (1968–1971) is oversquare — the 3.877" bore exceeds the 3.535" stroke by 9.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.535" stroke puts mean piston speed at 4,000 ft/min around 6,800 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.612 is in the range most production engines fall in. Each of the 6 cylinders displaces 41.7 ci (683 cc).
It is one of 5 engines in the Pontiac 250ci family, all of them 250 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated from 145 to 155 hp across 1968–1971.
| Displacement | 250 ci / 4.1 L |
|---|---|
| Bore | 3.877" |
| Stroke | 3.535" |
| Cylinders | 6 |
| Configuration | I6 |
| Rod length | 5.7" |
| Rod ratio | 1.612 |
| Bore/stroke ratio | 1.097 |
| Fuel type | gas |
|---|---|
| Advertised HP | 145–155 hp |
| Years | 1968–1971 |
| Bore/stroke character | 1.097 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,535 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.612 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 41.7 ci |
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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 |
|---|---|---|
| 1968 | 155 hp | — |
| 1969 | 155 hp | — |
| 1970 | 155 hp | — |
| 1971 | 145 hp | — |