See other engines in this family
Oldsmobile 151ci specs: 151 ci (2.5L) 4-cylinder, 4.002 x 3.01 in (101.7 x 76.5 mm) bore and stroke, 8.5:1 compression. Rated 90-110 hp, 1982–1992.
The Oldsmobile 151ci is oversquare — the 4.002" bore exceeds the 3.01" stroke by 33.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.01" stroke does not reach 4,000 ft/min of mean piston speed until about 7,950 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 2.01 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 4 cylinders displaces 37.8 ci (619 cc).
8.5:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Oldsmobile 151ci family, all of them 151 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated from 90 to 110 hp across 1982–1992.
| Displacement | 151 ci / 2.5 L |
|---|---|
| Bore | 4.002" |
| Stroke | 3.01" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 8.5:1 |
| Rod length | 6.05" |
| Rod ratio | 2.01 |
| Bore/stroke ratio | 1.33 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 90–110 hp |
| Years | 1982–1992 |
| Bore/stroke character | 1.330 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,010 ft/min — conservative for a street engine |
| Rod ratio | 2.01 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 37.8 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.72" |
|---|---|
| Exhaust valve diameter | 1.5" |
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 |
|---|---|---|
| 1982 | 90 hp | — |
| 1991 | 110 hp | — |
| 1992 | 110 hp | — |