A hemispherical combustion chamber is a combustion chamber in the cylinder head of an internal combustion engine with a domed "hemispheric" shape. An engine featuring this type of hemispherical chamber is known as a hemi engine. In practice, shapes less than a full hemisphere are typically employed, as are variations of a true hemispheric profile. The primary advantage of such shapes are increased compression and very large intake and exhaust valves ; the primary disadvantages are complex valve trains and expense.