The Jeep Tornado engine was the first post-World War II U.S.-designed mass-produced overhead cam (OHC) automobile engine. The 230.5 cu in (3.78 L) hemi-headed straight-six was introduced in mid-year 1962, and replaced the flathead "6-226" Willys Super Hurricane that was in use since 1954.

The inline-six engine is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine balance, resulting in fewer vibrations than other designs of six or fewer cylinders.