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Buick 401ci specs: 401 ci (6.6L) 8-cylinder, 4.188 x 3.64 in (106.4 x 92.5 mm) bore and stroke, 9:1 compression. Rated 265 hp, 1963.
The Buick 401ci is oversquare — the 4.188" bore exceeds the 3.64" stroke by 15.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.64" stroke puts mean piston speed at 4,000 ft/min around 6,600 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.709 is in the range most production engines fall in. Each of the 8 cylinders displaces 50.1 ci (821 cc).
9:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the Buick 401ci family, all of them 401 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 401 ci / 6.6 L |
|---|---|
| Bore | 4.188" |
| Stroke | 3.64" |
| Cylinders | 8 |
| Compression ratio | 9:1 |
| Rod length | 6.22" |
| Rod ratio | 1.709 |
| Bore/stroke ratio | 1.151 |
| Piston deck clearance | 0.028" |
| Induction | 1-2 |
|---|---|
| Advertised HP | 265 hp |
| Years | 1963 |
| Bore/stroke character | 1.151 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,640 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.709 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 50.1 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.875" |
|---|---|
| Exhaust valve diameter | 1.5" |
| Chamber volume | 123.72 cc |
| Rocker ratio | 1.6:1 |
| Lifter type | hydraulic |
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