A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head notionally in the approximate shape of a hemisphere (in reality usually a spheric section thereof). An engine featuring this type of hemispherical chamber is known as a hemi engine. History Hemispherical combustion chambers were introduced on some of the earliest automotive engines, shortly after the viability of the internal combustion engine was first demonstrated. Their name reflects the domed cylinder head and the top of the piston enclosing a space that approximates a half of a sphere (hemi- + -sphere + -ical), although in practice the actual enclosed space is generally less than half. Hemispherical cylinder heads have been used since at least 1901; they were used by the Belgian car maker Pipe in 1905 and by the 1907 Fiat 130 HP Grand Prix racer. The Peugeot Grand Prix car of 1912 and the Alfa Romeo Grand Prix car of 1914 were both four-valve engines, and Daimler and Riley were also using hemispherical combustion chambers at the time. Beginning in 1912, Stutz used four-valve engines, conceptually anticipating modern car engines. Other examples include the BMW double-pushrod design (adopted by Bristol Cars), the Peugeot 403, the Toyota T engine and Toyota V engine (Toyota's first V8 engine), Miller racing engines, and the Jaguar XK engine. Technology and implementation A hemispherical head ("hemi-head") gives an efficient combustion chamber with minimal heat loss to the head, and allows for two large valves. However, a hemi-head usually allows no more than two valves per cylinder due to the difficulty in arranging the valve gear for four valves at diverging angles, and these large valves are necessarily heavier than those in a multi-valve engine of similar valve area, as well as generally requiring more valve lift. The intake and exhaust valves lie on opposite sides of the chamber and necessitate a "cross-flow" head design. Since the combustion chamber is virtually a hemisphere, a flat-topped piston yields a lower compression ratio unless a smaller chamber is utilized. Significant challenges in the commercialization of engines utilizing hemispherical chambers revolved around the design of the valve actuation, and how to make it effective, efficient, and reliable at an acceptable cost, which normally requires the use of either a dual rocker system, or dual camshafts to operate the inlet and exhaust valves. Complexity was referenced early in Chrysler's