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Oldsmobile 138ci specs: 138 ci (2.3L) 4-cylinder, 3.625 x 3.35 in (92.1 x 85.1 mm) bore and stroke, 11:1 compression. Rated 115-180 hp, 1989–1993.
The Oldsmobile 138ci is oversquare — the 3.625" bore exceeds the 3.35" stroke by 8.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.35" stroke does not reach 4,000 ft/min of mean piston speed until about 7,150 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.734 is in the range most production engines fall in. Each of the 4 cylinders displaces 34.5 ci (565 cc).
11:1 on iron heads is high enough that pump premium or better is normally required, and iron holds heat, so it is the less forgiving side of that line.
It is one of 3 engines in the Oldsmobile 138ci family, all of them 138 ci — the differences between them are in compression, heads and rating, not displacement. 9 factory variants share these dimensions, rated from 115 to 180 hp across 1989–1993.
| Displacement | 138 ci / 2.3 L |
|---|---|
| Bore | 3.625" |
| Stroke | 3.35" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 11:1 |
| Rod length | 5.81" |
| Rod ratio | 1.734 |
| Bore/stroke ratio | 1.082 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 115–180 hp |
| Years | 1989–1993 |
| Bore/stroke character | 1.082 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,350 ft/min — conservative for a street engine |
| Rod ratio | 1.734 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 34.5 ci |
| Static compression | 11:1 — 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 |
|---|---|---|
| 1989 | 150 hp | — |
| 1990 | 150 hp | — |
| 1991 | 150 hp | — |
| 1992 | 120 hp | — |
| 1992 | 160 hp | — |
| 1992 | 180 hp | — |
| 1993 | 115 hp | — |
| 1993 | 155 hp | — |
| 1993 | 175 hp | — |