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Oldsmobile 400 (Small Block) specs: 400 ci (6.6L) 8-cylinder, 3.87 x 4.25 in (98.3 x 108 mm) bore and stroke, 10.5:1 compression. Rated 325 hp. OHV.
The Oldsmobile 400 (Small Block) is undersquare — the 4.25" stroke exceeds the 3.87" bore by 8.9% — a layout that trades peak RPM for leverage and torque low in the range. The 4.25" stroke puts mean piston speed at 4,000 ft/min around 5,650 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).
10.5:1 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 15 engines in the Rocket family, sitting between the 260 ci and 455 ci members. Factory fitments include the Oldsmobile 442, Oldsmobile Cutlass.
| Displacement | 400 ci / 6.6 L |
|---|---|
| Bore | 3.87" |
| Stroke | 4.25" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 0.911 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 325 hp |
| Bore/stroke character | 0.911 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,250 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 50.0 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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