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Cadillac 390 specs: 390 ci (6.4L) 8-cylinder, 4.00 x 3.874 in (101.6 x 98.4 mm) bore and stroke, 10.5:1 compression. Rated 325 hp. Rod ratio and piston speed.
The Cadillac 390 Series (390) is close to square: 4" bore against 3.874" stroke, within 3.3%, which splits the difference between a high-revving layout and a torque layout. The 3.874" stroke puts mean piston speed at 4,000 ft/min around 6,200 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 48.8 ci (799 cc).
10.5:1 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.
Factory fitments include the Series 62, Eldorado, DeVille and 3 others.
| Displacement | 390 ci / 6.4 L |
|---|---|
| Bore | 4" |
| Stroke | 3.874" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 1.033 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 325 hp |
| Bore/stroke character | 1.033 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,874 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 48.8 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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