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The same engine also has a main page: Jeep 242.
Jeep 40 AMC I6 HO specs: 242 ci (4.0L) 6-cylinder, 3.874 x 3.413 in (98.4 x 86.7 mm) bore and stroke, 8.8:1 compression. Rated 190 hp. OHV.
The Jeep 40 AMC I6 HO is oversquare — the 3.874" bore exceeds the 3.4134" stroke by 13.5% — a layout that favors airflow and RPM over leverage at the crank. The 3.4134" stroke does not reach 4,000 ft/min of mean piston speed until about 7,050 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 40.3 ci (661 cc).
8.8:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 7 engines in the AMC I6 family, sitting between the 232 ci and 258 ci members. Factory fitments include the Wrangler TJ, Cherokee XJ, Grand Cherokee ZJ and 16 others.
| Displacement | 242 ci / 4 L |
|---|---|
| Bore | 3.874" |
| Stroke | 3.4134" |
| Cylinders | 6 |
| Compression ratio | 8.8:1 |
| Bore/stroke ratio | 1.135 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 190 hp |
| Bore/stroke character | 1.135 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,413 ft/min — conservative for a street engine |
| Displacement per cylinder | 40.3 ci |
| Static compression | 8.8:1 — low by modern standards, generally happy on regular pump fuel |
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