What is a hemi?

"Hemi" is short for hemispherical combustion chamber. It refers to a type of engine design where the combustion chamber's shape is roughly half a sphere (hemisphere). This design has several implications:

• Improved Combustion: The hemispherical shape promotes a more efficient and complete burn of the air-fuel mixture. This is because the spark plug is centrally located, allowing for a more even flame front propagation. This leads to better power and fuel efficiency compared to some other designs.

• High Performance: Hemi engines are generally known for their high power output for their displacement. This is due to the efficient combustion and design characteristics.

• Valvetrain: Hemi engines typically feature a unique valvetrain arrangement. The valves are often angled inwards, often with two valves per cylinder on each side of the combustion chamber (intake and exhaust), nestled within the hemispherical space. This contributes to better airflow and combustion.

• Chrysler Hemi: The term "Hemi" is most strongly associated with Chrysler's line of engines. These engines have a long and storied history, known for their high performance and use in muscle cars. However, other manufacturers have also used hemispherical combustion chambers in their engines.

• Disadvantages: Hemi engines can sometimes be more complex and expensive to manufacture than other engine designs. They may also be less fuel-efficient at lower engine speeds compared to some other modern designs, although this can depend on the specific engine's specifications and technology.

In short, a hemi engine is a specific type of internal combustion engine known for its powerful, efficient combustion process thanks to its characteristic hemispherical combustion chamber shape. While the Chrysler Hemi is the most famous example, the term describes a design principle applicable to various engine types.