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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 ...
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.
A popular modification to the early 22R is to use a 20R head. Contrary to popular lore, the 20R head does not have smaller combustion chambers. The misunderstanding originated when the 22R came out and an advantage was its higher compression ratio, so swapping a 20R block with a 22R, there was a compression increase.
Common shapes for the combustion chamber are typically similar to one or more half-spheres (such as the hemi, pent-roof, wedge or kidney-shaped chambers). The older flathead engine design uses a "bathtub"-shaped combustion chamber, with an elongated shape that sits above both the piston and the valves (which are located beside the piston).
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.
All T engines utilize a timing chain and have a cast iron block with an alloy cylinder head with hardened valve seats and a hemispherical combustion chamber design . All T engines are carburetted except those with electronic fuel injection, "E" designation.
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.
These combustion chambers were formed by the two shallow concave domes where the intake and exhaust valve seats were. [ 1 ] Because these engines needed a less sophisticated rocker setup, with only a single rocker shaft in each head, they were also cheaper and lighter than their Hemi counterparts.