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Oldsmobile LT6 specs: 262 ci (4.3L) 6-cylinder, 4.057 x 3.385 in (103 x 86 mm) bore and stroke, 21.6:1 compression. Rated 85 hp. Used in the Buick Regal. OHV.
The Oldsmobile Diesel (LT6) is oversquare — the 4.057" bore exceeds the 3.385" stroke by 19.9% — a layout that favors airflow and RPM over leverage at the crank. 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 6 cylinders displaces 43.7 ci (716 cc).
At 21.6:1 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 largest at 262 ci. Factory fitments include the Oldsmobile Cutlass Ciera, Oldsmobile Delta 88.
| Displacement | 262 ci / 4.3 L |
|---|---|
| Bore | 4.057" |
| Stroke | 3.385" |
| Cylinders | 6 |
| Compression ratio | 21.6:1 |
| Bore/stroke ratio | 1.199 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 85 hp |
| Bore/stroke character | 1.199 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,385 ft/min — conservative for a street engine |
| Displacement per cylinder | 43.7 ci |
| Static compression | 21.6:1 — high enough that pump premium or better is normally required |
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