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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.
In a hemispherical cylinder head, when air enters the combustion chamber through the intake valve, it flows to the exhaust valve instead of being forced through the exhaust valve as pressure is built up in the combustion chamber. While Tom Hoover developed the 426 Hemi engine, cylinder heads can be interchanged between specific engines.
It is similar in concept to the hemi engine, both in design and purpose, but a hemispherical cylinder head is limited to only two valves without the use of a more complex sub-rocker assembly. The four-valve penta engine design was invented by Peugeot of France, [ citation needed ] to be first used in the 1911 Indianapolis 500 race.
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.
Forged connecting rods used the Wedge's 3 ⁄ 8 in (9.5 mm) hardware, as opposed to the Hemi's 7 ⁄ 16 in (11.1 mm), but would nonetheless have been considered high-performance parts. [ 1 ] The intake was to be a single Carter ThermoQuad , of greater flow than any previously used, on a dual-plane intake manifold, [ 5 ] while dual four-barrels ...
The Polyspheric or Poly engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to the Hemi engines. [1] These engines were based on the Hemi engines, using the same blocks and crankshaft parts, but completely different cylinder heads, pushrods, exhaust manifolds and pistons.
Donovan developed the 417 cu in (6,830 cc) hemi-head V8 to overcome the tendency of 392 cu in (6,420 cc) Chryslers, then used by Top Fuel racers (many of them friends and customers of his), to crack their iron blocks. [1] He copied the 392 cu in (6,420 cc), which he admired, but tried to eliminate its deficiencies. [2]