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Ford 390ci specs: 390 ci (6.4L) 8-cylinder, 4.052 x 3.784 in (102.9 x 96.1 mm) bore and stroke, 11.3:1 compression. Rated 320 hp, 1970.
The Ford 390ci is oversquare — the 4.052" bore exceeds the 3.784" stroke by 7.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.784" stroke puts mean piston speed at 4,000 ft/min around 6,350 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.715 is in the range most production engines fall in. Each of the 8 cylinders displaces 48.8 ci (799 cc).
11.3:1 is high enough that pump premium or better is normally required.
It is one of 21 engines in the Ford 390ci family, all of them 390 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 390 ci / 6.4 L |
|---|---|
| Bore | 4.052" |
| Stroke | 3.784" |
| Cylinders | 8 |
| Compression ratio | 11.3:1 |
| Rod length | 6.488" |
| Rod ratio | 1.715 |
| Bore/stroke ratio | 1.071 |
| Piston deck clearance | 0.001" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 320 hp |
| Years | 1970 |
| Bore/stroke character | 1.071 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,784 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.715 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 48.8 ci |
| Static compression | 11.3:1 — high enough that pump premium or better is normally required |
| Intake valve diameter | 2.037" |
|---|---|
| Exhaust valve diameter | 1.566" |
| Chamber volume | 63.5 cc |
| Rocker ratio | 1.73:1 |
| Lifter type | hydraulic |
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