Hemispherical Combustion Chamber (Hemi)
A hemi head has a dome-shaped combustion chamber with valves on opposite sides, allowing large valves and good airflow.
What is Hemispherical Combustion Chamber (Hemi)?
Chrysler’s HEMI engines made the name well known. Many engines use a similar but modified design. It favours high power output. Early hemi designs date back to the early 20th century.
How it works
The dome shape gives room for large, angled valves and a short flame path.
Why it matters for your car
The shape can make complete combustion and emissions control harder. Head and valve parts are specific to the design.
Other terms
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