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Jeep 401 specs: 401 ci (6.6L) 8-cylinder, 4.311 x 3.44 in (109.5 x 87.4 mm) bore and stroke, 8.2:1 compression. Rated 215 hp. OHV. Rod ratio and piston speed.
The Jeep AMC V8 (401) is oversquare — the 4.311" bore exceeds the 3.4402" stroke by 25.3% — a layout that favors airflow and RPM over leverage at the crank. The 3.4402" stroke puts mean piston speed at 4,000 ft/min around 7,000 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 50.1 ci (821 cc).
8.2:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 7 engines in the AMC V8 family, the largest at 401 ci. Factory fitments include the Jeep J-Series Truck, Jeep Wagoneer (SJ), Jeep Cherokee (SJ).
| Displacement | 401 ci / 6.6 L |
|---|---|
| Bore | 4.311" |
| Stroke | 3.4402" |
| Cylinders | 8 |
| Compression ratio | 8.2:1 |
| Bore/stroke ratio | 1.253 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 215 hp |
| Bore/stroke character | 1.253 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,440 ft/min — conservative for a street engine |
| Displacement per cylinder | 50.1 ci |
| Static compression | 8.2:1 — low by modern standards, generally happy on regular pump fuel |
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