In a HEMI engine, the top of the combustion chamber is hemispherical. The combustion area in the head is shaped like half of a sphere, unlike most engines where the head has small indentations for the combustion chamber. An engine like this is said to have “hemispherical heads.” In a HEMI head, the spark plug is normally located at the top of the combustion chamber, and the valves open on opposite sides of the combustion chamber.
Gerald Wheelus
Edgewood Auto Parts #253
Edgewood, Texas