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Chevrolet 400ci specs: 400 ci (6.6L) 8-cylinder, 4.125 x 3.75 in (104.8 x 95.3 mm) bore and stroke, 10.201:1 compression. Rated 175-180 hp, 1974–1975.
The Chevrolet 400ci is oversquare — the 4.125" bore exceeds the 3.75" stroke by 10.0% — a layout that favors airflow and RPM over leverage at the crank. The 3.75" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.485 is short — higher piston acceleration and more side-load, typical of stroker combinations and a reason to watch piston speed closely. Each of the 8 cylinders displaces 50.0 ci (819 cc).
10.201:1 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 7 engines in the Chevrolet 400ci family, all of them 400 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated from 175 to 180 hp across 1974–1975.
| Displacement | 400 ci / 6.6 L |
|---|---|
| Bore | 4.125" |
| Stroke | 3.75" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 10.201:1 |
| Rod length | 5.57" |
| Rod ratio | 1.485 |
| Bore/stroke ratio | 1.1 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 175–180 hp |
| Years | 1974–1975 |
| Bore/stroke character | 1.100 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,750 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.485 — short — more side loading and piston dwell at TDC, typical of stroker combinations |
| Displacement per cylinder | 50.0 ci |
| Static compression | 10.201:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.945" |
|---|---|
| Exhaust valve diameter | 1.505" |
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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 |
|---|---|---|
| 1974 | 180 hp | — |
| 1975 | 175 hp | — |