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Buick 400ci specs: 400 ci (6.6L) 8-cylinder, 4.04 x 3.90 in (102.6 x 99.1 mm) bore and stroke, 10.25:1 compression. Rated 340-350 hp, 1967–1969.
The Buick 400ci is close to square: 4.04" bore against 3.9" stroke, within 3.6%, which splits the difference between a high-revving layout and a torque layout. The 3.9" stroke puts mean piston speed at 4,000 ft/min around 6,150 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.694 is in the range most production engines fall in. Each of the 8 cylinders displaces 50.0 ci (819 cc).
10.25:1 is in the range that usually runs on pump premium.
It is one of 3 engines in the Buick 400ci family, all of them 400 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated from 340 to 350 hp across 1967–1969.
| Displacement | 400 ci / 6.6 L |
|---|---|
| Bore | 4.04" |
| Stroke | 3.9" |
| Cylinders | 8 |
| Compression ratio | 10.25:1 |
| Rod length | 6.607" |
| Rod ratio | 1.694 |
| Bore/stroke ratio | 1.036 |
| Piston deck clearance | 0.01" |
| Induction | 1-4 |
|---|---|
| Advertised HP | 340–350 hp |
| Years | 1967–1969 |
| Bore/stroke character | 1.036 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,900 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.694 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 50.0 ci |
| Static compression | 10.25:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 2" |
|---|---|
| Exhaust valve diameter | 1.63" |
| Chamber volume | 67.6 cc |
| Rocker ratio | 1.6:1 |
| 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 |
|---|---|---|
| 1967 | 340 hp | — |
| 1968 | 340 hp | — |
| 1969 | 340 hp | — |
| 1969 | 350 hp | — |