Polysphere (pronounced pol-ee-sfeer)
(1) In mathematics, a product of spheres.
(2) In mechanical engineering, a design of combustion chamber formed by the two shallow concave domes under the intake and exhaust valve seats.
1955: A compound word, the construct being poly + sphere. Poly is from the Ancient Greek πολύς (polús or polys) (many, much), from the primitive Indo-European polhiús (much, many) from the root pele (to fill), akin to the Old English fela (many). Sphere is from the Middle English spere, from the Old French spere, from the Late Latin sphēra, from the Classical Latin sphaera (ball, globe, celestial sphere), from the Ancient Greek σφαῖρα (sphaîra) (ball, globe), of unknown origin. Despite spread of the myth by some medieval writes, sphere is not related to superficially similar Persian سپهر (sepehr) (sky). Poly, in modern English (especially in industrial and scientific application) use became a word-forming element meaning "many, much, multi-, one or more" with derivatives referring to multitudinousness or abundance. It was equivalent to the Latin multi- and should properly be used in compounds only with words of Greek origin but this, etymologically slutty English ignores. Polysphere is a noun and polyspheric is an adjective; the noun plural is polyspheres.
Lindsay Lohan with polyspheric hair. Polyspheric hair styles are possible, the classic example of which is the symmetrical “twin dome” look which is difficult exactly to achieve and harder still to maintain for more than a brief time. They’re thus seen usually only at photo-shoots or for one-off events but the design element is popular with asymmetric styles.
Chrysler, the poly, the hemi and the hemi which is really a poly
Chrysler didn’t invent hemispherical combustion chambers but they certainly made a cult of them. In internal combustion engines (ICE) of the mid-late twentieth century, especially as the availability of higher octane gas (petrol) made possible higher compression ratios, the hemispherical combustion chamber was one of the best designs with with to provide an efficient burn-space while minimizing thermal loss and permitting the use of large diameter, canted-valves to optimize intake and exhaust flow. The early Chrysler Hemi V8s (1951-1958) were the most powerful of their generation but there were drawbacks. To take advantage of the large valves at diverging angles, the valve train assembly was both bulky and heavy, needing two rocker shafts rather than the single unit possible with in-line arrangements and adding to the cost and complication were the inherently more expensive casting and machining processes required to produce the hemispherical shape of the combustion chambers in the cylinder heads. To enable the mass-production of a less expensive V8 to use in their lower-priced lines, Chrysler created new cylinder heads with what they named polyspheric (two shallow concave domes under the in-line valves) which, as a companion to the Hemi, quickly was nicknamed "“Poly”. Although less powerful than the Hemis, the Polys, with more quickly machined combustion chambers and a single rocker shaft, enjoyed significantly lower unit production costs so the economics were attractive although it wouldn’t be until the 1960s Chrysler standardized engines across their divisions; an early adoption of such economies of scale might have saved the corporation more money than retaining an exclusively Hemi-headed line would have cost.
The Hemi, 1951-1958 & 1964-1971 (left), the Polyspheric, 1955-1967 (centre) and the new "Hemi" which is really a swirl Chamber, 2003- (right).
The Poly however proved a cul-de-sac. In an era of cheap gas, larger capacity engines proved a more attractive route to horsepower than sophisticated combustion chamber design and the Hemis were retired in 1958, replaced by engines of larger displacement with wedge-shaped chambers, used by other manufacturers and much more suited to mass-production. Consigned to the grave with the Hemi were almost all the Polys, only the 318 V8 (5.2 litre) retained as a rare oddity until 1967. The Hemi would in 1964 return, available as a 426 cubic inch (7.0 litre) race engine (there were also some reduced displacement versions to satisfy local rules) which, for homologation purposes would in 1966 be released in (slightly) detuned form detuned for street use, remaining an expensive option in certain Dodges and Plymouths until 1971. The name however held such an allure it was in 2003 revived in 2003 (although the corporation's Australian arm between 1970-1981 produced a straight-six "Hemi" (which was really a "semi-hemi")) for Chrysler's new (and perhaps final) generation of V8s. Like the highly-regarded Australian engine, in the narrow technical sense, the use of "Hemi" for the new V8 (dubbed "Generation III to capitalize on the name's storied legacy") really was a marketing than an engineering term because the combustion chambers were something of a hemispheric cum polyspheric hybrid, the general term describing them for the last fifty-odd years being swirl chambers, a design which, in combination with modern electronic engine management systems (EMS), makes possible autput of power, low emissions and economy which would have been thought impossible to achieve as recently as the 1980s.
When Chrysler in 1964 introduced the 273 cubic inch (4.5 litre) V8 as the first of its LA-Series (that would begat the later 318, 340 & 360 (the V10 Magnum used in the Dodge Viper also as descendent)), the most obvious visual difference from the earlier A-Series V8s was the noticeably smaller cylinder heads. The A engines used a skew-type valve arrangement in which the exhaust valve was parallel to the bore with the intake valve tipped toward the intake manifold (the classic polyspherical chamber). For the LA, Chrysler rendered all the valves tipped to the intake manifold and in-line (as viewed from the front), the industry’s standard approach with a wedge combustion chamber. The reason for the change was the decision had been taken to offer the compact (in contemporary US terms; it would have seemed pretty big in most of the planet) Valiant with a V8 but it had been designed to accommodate only a straight-six and the wide-shouldered polyspheric head A-Series V8s simply wouldn’t fit. So, essentially, wedge-heads were bolted atop the old A-Series block but the “L” in LA stood for light and the engineers wanted something genuinely lighter for the Valiant. Accordingly, in addition to the reduced size of the heads and intake manifold, a new casting process was developed for the block (the biggest, heaviest part of an engine) which made possible thinner walls. With the exception of the Hemis, the new big-block engines used wedge-heads and the small block polyspheres (the A-Series) were replaced by the LA except for an export version of the 313 (5.1 litre) which, in small batches, was manufactured until 1965 and the 318, the last of which was fitted in 1967. Confusingly, the replacement LA engine was also a 318, a product of carrying over certain components, both the 318-A & 318-LA sharing the same bore & stroke. In an example of production-line rationalization, when Chrysler Australia bored out their 245 cubic inch (4.0 litre) Hemi-six to create the 265 (4.3), the bore chosen was the same as the 318s so pistons could have been shared with the V8 although for technical reasons this wasn't actually done. The Australian "Hemi" straight sixes used another variation of the combustion chamber in that chambers sat in upper third of the globe, hence the "low hemispherical" slang which wasn't wholly accurate but Ford's Boss 429 V8 had already been dubbed the "semi-hemi" and linguistic novelty was becoming hard to concoct.
Upon release in 1955, the Polyspheric V8s were thought such a novelty they generated much publicity, not only in trade or specialist publications but also in the mainstream press. Although not yet the “space age”, it was already the “jet age” and there was genuine public fascination with apparently new or innovative products, even if many were really variations of something old and the advertising copy was sometimes the most adventurous aspect. To help the journalists, included in Chrysler’s press-kits were full-color diagrams explain the theory, illustrating the unseen cycle of fluid dynamics happening under the hood (bonnet) thousands of times a second. However pleasing the graphics, not all were impressed by the name, Motor Trend magazine in their February 1955 edition publishing a letter from a Mr Hal Julian of Los Angeles whose objection was the word “polyspherical” didn’t exist and what Chrysler should have used was “hemispheroid” (used variously to mean (1) having a roughly hemispheric shape and (2) half of a spheroid), definitions of the latter appearing in dictionaries. However, while it may not have appeared in the shorter (abridged) dictionaries, polysphere (in mathematics & geometry “a product of spheres”) did have entries in both supplements to the twelve volume Oxford English Dictionary (1933) and Webster's New International Dictionary (1934) which weighed in with over 600,000 words and was an impressive eight-odd inches (200 mm) thick.
Drie bollen I (Three Spheres I), houtgravure (wood engraving) (1945) by Dutch graphic artist Maurits Cornelis "M.C." Escher (1898–1972). The final engraving (left) may be compared with the pencil on paper study (right). This was one of a number of works in which Escher explored how, with the greatest precision, a three-dimensional form could be represented on a flat surface.
Polyspherical seems first to have appeared in print in the 1920s in papers published by British physicist Sir Edmund Whittaker (1873–1956) and US physical chemist Gilbert Lewis (1875–1946), the latter remembered also for having in 1926 coined the word “photon” to describe the smallest unit of radiant energy. The two both used “polyspherical” in the context of what they termed “polyspherical coordinates”, used as devices to solve puzzles in partial differential equations in higher-dimensional spaces, an arcane field understood, even now, only by a few although most of us benefit from the implications. It’s a fork of the discipline replete with terms baffling to most but the experts note “polyspherical coordinates” by the mid-1930s became formalized in its use to refer to systems “generalizing spherical coordinates to higher dimensions using nested angular parametrizations”. Sounds simple enough.
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