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Buick 340 specs: 340 ci (5.6L) 8-cylinder, 3.75 x 3.85 in (95.3 x 97.8 mm) bore and stroke, 10.25:1 compression. Rated 260 hp. Rod ratio and piston speed.
The Buick Small-Block V8 (340) is close to square: 3.75" bore against 3.85" stroke, within 2.6%, which splits the difference between a high-revving layout and a torque layout. The 3.85" stroke puts mean piston speed at 4,000 ft/min around 6,250 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 42.5 ci (696 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 8 engines in the Buick Small-Block V8 family, sitting between the 300 ci and 350 ci members. Factory fitments include the Buick Skylark, Buick LeSabre, Buick Special and 2 others.
| Displacement | 340 ci / 5.6 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.85" |
| Cylinders | 8 |
| Compression ratio | 10.25:1 |
| Bore/stroke ratio | 0.974 |
| Piston deck clearance | 0.01" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 260 hp |
| Bore/stroke character | 0.974 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,850 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 42.5 ci |
| Static compression | 10.25:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.818" |
|---|---|
| Exhaust valve diameter | 1.38" |
| Chamber volume | 54.9 cc |
| Rocker ratio | 1.6:1 |
| Lifter type | hydraulic |
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