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Oldsmobile LF7 specs: 260 ci (4.3L) 8-cylinder, 3.70 x 3.07 in (94 x 78 mm) bore and stroke, 22.5:1 compression. Rated 85 hp. OHV. Rod ratio and piston speed.
The Oldsmobile Diesel (LF7) is oversquare — the 3.7" bore exceeds the 3.07" stroke by 20.5% — a layout that favors airflow and RPM over leverage at the crank. The 3.07" stroke does not reach 4,000 ft/min of mean piston speed until about 7,800 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 22.5:1 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 5 engines in the Diesel family, the smallest at 260 ci. Factory fitments include the Oldsmobile Cutlass, Oldsmobile Omega.
| Displacement | 260 ci / 4.3 L |
|---|---|
| Bore | 3.7" |
| Stroke | 3.07" |
| Cylinders | 8 |
| Compression ratio | 22.5:1 |
| Bore/stroke ratio | 1.205 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 85 hp |
| Bore/stroke character | 1.205 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,070 ft/min — conservative for a street engine |
| Displacement per cylinder | 32.5 ci |
| Static compression | 22.5:1 — high enough that pump premium or better is normally required |
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