See other engines in this family
Jeep 242 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. Rod ratio and piston speed.
The Jeep AMC Straight-6 (242) 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 14 engines in the AMC Straight-6 family, the smallest at 242 ci. Factory fitments include the Jeep Cherokee (XJ), Jeep Wrangler (YJ/TJ), Jeep Grand Cherokee (ZJ/WJ).
| 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 |
Each link opens the calculator with this engine's specs already filled in.