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Oldsmobile 305ci specs: 305 ci (5.0L) 8-cylinder, 3.736 x 3.484 in (94.9 x 88.5 mm) bore and stroke, 9.9:1 compression. Rated 170 hp, 1991–1992. OHV.
The Oldsmobile 305ci is oversquare — the 3.736" bore exceeds the 3.484" stroke by 7.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.484" stroke puts mean piston speed at 4,000 ft/min around 6,900 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.636 is in the range most production engines fall in. Each of the 8 cylinders displaces 38.1 ci (625 cc).
9.9:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 4 engines in the Oldsmobile 305ci family, all of them 305 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated at 170 hp across 1991–1992.
| Displacement | 305 ci / 5 L |
|---|---|
| Bore | 3.736" |
| Stroke | 3.484" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9.9:1 |
| Rod length | 5.7" |
| Rod ratio | 1.636 |
| Bore/stroke ratio | 1.072 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 170 hp |
| Years | 1991–1992 |
| Bore/stroke character | 1.072 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,484 ft/min — conservative for a street engine |
| Rod ratio | 1.636 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 38.1 ci |
| Static compression | 9.9:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.845" |
|---|---|
| Exhaust valve diameter | 1.505" |
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 |
|---|---|---|
| 1991 | 170 hp | — |
| 1992 | 170 hp | — |