The term “hemi” in engine nomenclature refers to a hemispherical combustion chamber. This design describes the shape of the space above the piston where the air-fuel mixture is compressed and ignited. The shape resembles half of a sphere, hence the prefix “hemi,” derived from the Greek word for “half.” An example would be an engine marketed as having a “hemi” design, indicating its combustion chambers are shaped in this manner.
This configuration provides several advantages, notably more space for larger valves positioned at an angle relative to the piston. This arrangement facilitates improved airflow into and out of the cylinder, resulting in enhanced volumetric efficiency. Historically, this design has been associated with increased power output and efficiency, contributing to its desirability in performance applications. This chamber geometry allows for a more centralized spark plug location, promoting a more complete and even burn of the air-fuel mixture.
