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Cadillac LD8 specs: 281 ci (4.6L) 8-cylinder, 3.661 x 3.307 in (93 x 84 mm) bore and stroke, 10:1 compression. Rated 275 hp. DOHC. Rod ratio and piston speed.
The Cadillac Northstar (LD8) is oversquare — the 3.6614" bore exceeds the 3.3071" stroke by 10.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.3071" stroke does not reach 4,000 ft/min of mean piston speed until about 7,250 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 35.1 ci (576 cc).
10:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
It is one of 4 engines in the Northstar family, the largest at 281 ci. Factory fitments include the Cadillac DeVille, Cadillac Seville, Cadillac Eldorado and 5 others.
| Displacement | 281 ci / 4.6 L |
|---|---|
| Bore | 3.6614" |
| Stroke | 3.3071" |
| Cylinders | 8 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.107 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 275 hp |
| Bore/stroke character | 1.107 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,307 ft/min — conservative for a street engine |
| Displacement per cylinder | 35.1 ci |
| Static compression | 10:1 — in the range that usually runs on pump premium |
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