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The hemi head always has intake and exhaust valve stems that point in different directions, requiring a large, wide cylinder head and complex rocker arm geometry in both cam-in-block and single overhead cam engines (dual overhead cam engines may not have rocker arms). This adds to the overall width of the engine, limiting the vehicles in which ...
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 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 big bore allowed for larger, 2.08 in (53 mm), intake valves, and the relatively short stroke helped it to be a free-revving and free-breathing engine. Producing a maximum of 330 hp (246 kW; 335 PS) and 460 lb⋅ft (624 N⋅m) of torque for the 1960 model year, the 383 beat the 392 Hemi that had reached 435 lb⋅ft (590 N⋅m).
The firing order of older big-block engines is 1-8-4-3-6-5-7-2 [62] while Vortec 8100's firing order is 1-8-7-2-6-5-4-3. Other upgrades of Vortec 8100 include a new 18-bolt head bolt pattern, longer connecting rods, different symmetrical intake ports, different oil pan rails, and the use of metric threads throughout the engine.
2003–present: Hemi. 5.7L Hemi - The smallest modern Hemi engine, called the Eagle, introduced in 2002. 6.1L Hemi - A larger modern Hemi, 2004–2010. 6.4L Hemi - A larger bore modern Hemi engine, called the Apache, introduced in 2011. 6.2L Hemi - A supercharged Hemi engine, called the Hellcat, introduced in 2014.
The valve size increased as well, to 2.11 in (53.6 mm) intake and 1.77 in (45.0 mm) exhaust valves on high-performance heads. Low-performance and two-barrel applications, the standard engine in full-sized Pontiacs, got 1.96 in (49.8 mm) intake and 1.66 in (42.2 mm) exhaust valves and pressed in rocker arm studs.
The new cylinder heads also featured stud-mounted rocker arms, a change from the shaft-mounted LA arms. This last change was due to the different oiling system of the new engine, as described in the next paragraph. [10] The valve covers on the Magnum have 10 bolts rather than the previous 5, for improved oil sealing. [12]