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Buick 231ci specs: 231 ci (3.8L) 6-cylinder, 3.80 x 3.40 in (96.5 x 86.4 mm) bore and stroke, 11.8:1 compression. Rated 195-205 hp, 1996–1999.
The Buick 231ci is oversquare — the 3.8" bore exceeds the 3.4" stroke by 11.8% — 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 1.753 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 38.5 ci (631 cc).
11.8:1 on iron heads 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 12 engines in the Buick 231ci family, all of them 231 ci — the differences between them are in compression, heads and rating, not displacement. 5 factory variants share these dimensions, rated from 195 to 205 hp across 1996–1999.
| Displacement | 231 ci / 3.8 L |
|---|---|
| Bore | 3.8" |
| Stroke | 3.4" |
| Cylinders | 6 |
| Configuration | V6 |
| Compression ratio | 11.8:1 |
| Rod length | 5.96" |
| Rod ratio | 1.753 |
| Bore/stroke ratio | 1.118 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 195–205 hp |
| Years | 1996–1999 |
| Bore/stroke character | 1.118 — 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 | 1.753 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 38.5 ci |
| Static compression | 11.8:1 — high enough that pump premium or better is normally required |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1996 | 205 hp | — |
| 1997 | 195 hp | — |
| 1997 | 205 hp | — |
| 1998 | 195 hp | — |
| 1999 | 195 hp | — |