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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 ...
In 1942-43, a range of configurations was considered and it was concluded that, for good breathing and high brake mean effective pressure (BMEP), the new engines would need vee-opposed valves operating in hemispherical combustion chambers. Two configurations of this type were selected for comparison in 1943 and the prototypes named "XG" and "XF".
The 90 degree V8 engine has a cast iron block, a short, stiff, dynamically balanced crankshaft carried on five bearings, light-alloy heads [3] with part-hemispherical combustion chambers, and two push-rod operated overhead valves per cylinder operated by a single chain-driven camshaft positioned centrally high up in the vee. [13]
Chrysler developed its first experimental hemi engine for the Republic P-47 Thunderbolt fighter aircraft. The XIV-2220 was an inverted V16 rated at 2,500 hp (1,860 kW). The P-47 was already in production with a Pratt & Whitney radial engine when the XIV-2220 flew successfully in trials in 1945 as a possible upgrade, but the war was winding down and it did not go into production.
Multi-point fuel injection and hemispherical combustion chambers are features of the 1986 Escort GT's EFI HO engine, raising output to 108 hp (81 kW) and 114 lb⋅ft (155 N⋅m). The 90 hp (67 kW) 1.9 L CFI engine of the late 1980s, particularly when equipped with either the four- or five-speed manual transaxle , was noted for delivering ...
IOE engines combine elements of overhead valve and flathead engines; the intake valve is located above the combustion chamber, while the exhaust valve is located below it. The shape of the combustion chamber, intake ports and exhaust ports are key to achieving efficient combustion and maximising power output.
The cylinder head has four hemispherical combustion chambers, each with two valves having an included angle of slightly over 73°, with the exhaust valves being inclined from the horizontal about 4° more than the intakes. The valves are made of nimonic steel, and have double valve springs. The camshafts are hollow, and run in five bearings each.
The Hemi-6 is a pushrod O.H.V. (overhead valve engine), with combustion chambers comprising about 35% of the top of the globe. This creates what is known as a low hemispherical shaped chamber. In this way, the "Hemi" moniker was used for the same kind of marketing cachet as Chrysler's 1950s-1970s Hemi V8 engines.