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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 ...
The engine's name is an acronym for either Compound Valve-angle Hemispherical or Canted Valve Hemispherical, where "Hemispherical" describes the shape of the combustion chamber. [ 1 ] [ 2 ] The CVH was introduced in 1980 in the third generation European Escort and in 1981 in the first generation North American Escort .
The current-production "HEMI" engine heads are flatter and more complex than the 1950s–'70s Hemi V8 chamber. The combustion chambers are no longer truly hemispherical. It uses a coil-on-plug (distributor-less) ignition system and two spark plugs per cylinder to shorten flame travel leading to more consistent combustion and reduced emissions ...
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.
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.
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".
Brian Henniker, courtesy of Gooding & Company. Through that six-year production run, the V-twin bikes gained a second oil cooler and ditched the hemispherical combustion chamber for a more typical ...
While the Twin Cam shared some features with the 1900 engine, it was a new design by Giuseppe Busso. [1] The Alfa Romeo Twin Cam engine debuted in the 1954 Giulietta. The engine featured: An aluminium alloy engine block with cast iron "wet" cylinder liners; An aluminium alloy cylinder head with hemispherical combustion chambers.