When Billy T. showed up at the Sunoco station with a clean, black '57 Plymouth Savoy one night in 1962, nobody looked twice. When he popped the hood, though, the excitement could be heard clear over in the next town. He had a big, fat 392 Hemi in there! With quads! The 800 pounds of iron over the front wheels meant that it was nose-heavy, but boy did that sucker roar on the top end. Though Billy had performed a fairly simple engine swap, the engine he swapped in was just like the one Don Garlits used to smoke his Fueler's tires the length of the dragstrip. We'd seen that happen, and it was scary impressive. Billy had inadvertently tapped into an icon... and the intimidation factor that went with it.
Hemi. The name continues to elicit thoughts of a monster, an insurmountable foe, King Kong teasing Faye Ray in the palm of his hand; yes, it was the one to beat. In an effort to understand the cachet and the reasons behind the Hemi's mythical status, we referenced "New Horizons In Engine Development," written by James Zeder for the May '52 issue of HOT ROD. Zeder was a VP and the director of engineering and research at Chrysler, and his division was responsible for the Fire Power Hemi engine, which was developed in 1948 and introduced to the public in the 1951 car model line (fall of 1950).
At that time, the spherical combustion chamber had been around for about 50 years, and perhaps even longer than that. With this configuration in mind, Chrysler examined the two popular schools of thought. The first was the classic chemical approach of improving engine efficiency and power primarily by increasing the compression ratio, which was then necessarily dependent on improvements in the fuel performance number. It had already surmised that such a dependency would stifle major advances in engine performance for some time to come.
The second argument was a mechanical approach in which increased efficiency and performance were sought through changes in the design of the engine without being dependent on fuel quality that characterized the compression ratio technique. As the engineering team went further, it became evident that the criterion of octane requirement at a given compression ratio was meaningless. The most important thing was the octane requirement for a given engine performance.
Originally, the team built a six-cylinder engine with hemispherical combustion chambers and twin, chaindriven overhead camshafts, but the cost and serviceability was not suitable for high production numbers. That idea was abandoned, but the Hemi project came back on line when the guys adapted pushrods to it. By doing so, they reduced the cost of production and restored servicing to the simple procedures of a conventional engine with no sacrifice to the fundamental attraction of the hemispherical combustion chamber.
They were quite enthusiastic about the Hemi's exclusive qualities. The laterally opposed valves permitted large, unobstructed, cool ports and unequalled volumetric efficiency. Compared to the best conventional combustion chamber, the higher thermal efficiency of the Hemi head was equivalent to a substantial increase in compression ratio and accomplished without an increase in octane. The relative absence of carbon buildup over time in the combustion chamber afforded a low level of detonation and pre-ignition, thus improving valve life. Fourth on the hit parade was the fact that heat rejection to the cooling system was at least 20 percent less than the best conventional OHV combustion chamber. In all, they were assured that when high compression became desirable, this cylinder head would respond to the increased demands on it better than any other combustion chamber of their acquaintance.