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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, 10.5:1 compression. Rated 265-325 hp, 1968–1970.
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).
10.5:1 is in the range that usually runs on pump premium.
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. 6 factory variants share these dimensions, rated from 265 to 325 hp across 1968–1970.
| Displacement | 390 ci / 6.4 L |
|---|---|
| Bore | 4.052" |
| Stroke | 3.784" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Rod length | 6.488" |
| Rod ratio | 1.715 |
| Bore/stroke ratio | 1.071 |
| Piston deck clearance | 0.0005" |
| Induction | 1-2 |
|---|---|
| Advertised HP | 265–325 hp |
| Years | 1968–1970 |
| 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 | 10.5:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 2.037" |
|---|---|
| Exhaust valve diameter | 1.566" |
| Chamber volume | 68.1 cc |
| Rocker ratio | 1.73:1 |
| Lifter type | hydraulic |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1968 | 280 hp | — |
| 1968 | 315 hp | — |
| 1968 | 325 hp | — |
| 1969 | 280 hp | — |
| 1969 | 320 hp | — |
| 1970 | 265 hp | — |