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Buick 400 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 hp. Rod ratio and piston speed.
The Buick Big-Block V8 (400) 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. Each of the 8 cylinders displaces 50.0 ci (819 cc).
10.25:1 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.
It is one of 3 engines in the Buick Big-Block V8 family, the smallest at 400 ci. Factory fitments include the Buick GS 400, Buick Riviera, Buick Wildcat and 4 others.
| Displacement | 400 ci / 6.6 L |
|---|---|
| Bore | 4.04" |
| Stroke | 3.9" |
| Cylinders | 8 |
| Compression ratio | 10.25:1 |
| Bore/stroke ratio | 1.036 |
| Piston deck clearance | 0.01" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 340 hp |
| 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 |
| 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 |
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