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Buick 340ci specs: 340 ci (5.6L) 8-cylinder, 3.75 x 3.85 in (95.3 x 97.8 mm) bore and stroke, 9:1 compression. Rated 220 hp, 1966–1967.
The Buick 340ci 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. A rod ratio of 1.659 is in the range most production engines fall in. Each of the 8 cylinders displaces 42.5 ci (696 cc).
9:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the Buick 340ci family, all of them 340 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated at 220 hp across 1966–1967.
| Displacement | 340 ci / 5.6 L |
|---|---|
| Bore | 3.75" |
| Stroke | 3.85" |
| Cylinders | 8 |
| Compression ratio | 9:1 |
| Rod length | 6.387" |
| Rod ratio | 1.659 |
| Bore/stroke ratio | 0.974 |
| Piston deck clearance | 0.01" |
| Induction | 1-2 |
|---|---|
| Advertised HP | 220 hp |
| Years | 1966–1967 |
| 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 |
| Rod ratio | 1.659 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 42.5 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
| 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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These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1966 | 220 hp | — |
| 1967 | 220 hp | — |