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Oldsmobile LF7 specs: 260 ci (4.3L) 8-cylinder, 3.50 x 3.385 in (88.9 x 86 mm) bore and stroke, 7.5:1 compression. Rated 90 hp, 1979.
The Oldsmobile 260ci (LF7) is close to square: 3.5" bore against 3.385" stroke, within 3.4%, which splits the difference between a high-revving layout and a torque layout. The 3.385" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 32.5 ci (533 cc).
At 7.5:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 4 engines in the Oldsmobile 260ci family, all of them 260 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 260 ci / 4.3 L |
|---|---|
| Bore | 3.5" |
| Stroke | 3.385" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 7.5:1 * |
| Bore/stroke ratio | 1.034 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | diesel |
|---|---|
| Advertised HP | 90 hp |
| Years | 1979 |
| Bore/stroke character | 1.034 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,385 ft/min — conservative for a street engine |
| Displacement per cylinder | 32.5 ci |
| Static compression | 7.5:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
1 factory vehicle, 1979. Each year opens that model's engine table.