Sonoramic (pronounced sonn-o-ram-ick)
A
form of enhanced induction for internal combustion engines; sometimes called cross-ram
or long-ram induction.
1959: A compound word constructed by engineers (apparently
with no contribution from the marketing department), the construct being the
Latin sonō (make a noise, sound) + the English ram + -ic. Sonō was from the primitive Indo-European
swenhe (to sound, resound) which was cognate with the Sanskrit स्वनति
(svanati) (to sound, resound). The more
productive Latin derivative was Latin sonus (sound, a noise) from the primitive
Indo-European swon-o, again from the root swenhe. Ram was from the Old English ramm (in
the sense of "battering ram", from the Old High German ram,
thought probably related to the Old Norse rammr (strong) and the Old
Church Slavonic ramenu (impetuous, violent). The suffix -ic is from the Middle English -ik, from the Old French -ique, from the Latin -icus, from the primitive Indo-European
-kos & -ḱos, formed with the i-stem suffix -i- and the
adjectival suffix -kos & -ḱos. The form existed also in the Ancient Greek as
-ικός (-ikós), in Sanskrit as -इक
(-ika) and the Old Church Slavonic as
-ъкъ (-ŭkŭ); A doublet of -y. In European languages, adding -kos to noun stems carried the meaning
"characteristic of, like, typical, pertaining to" while on adjectival
stems it acted emphatically; in English it's always been used to form
adjectives from nouns with the meaning “of or pertaining to”. A precise technical use exists in physical
chemistry where it's used to denote certain chemical compounds in which a
specified chemical element has a higher oxidation number than in the equivalent
compound whose name ends in the suffix -ous; (eg sulphuric acid (H₂SO₄)
has more oxygen atoms per molecule than sulphurous acid (H₂SO₃). The engineers were influenced in their coining
of sonoramic by the debut three years earlier of the sonogram (thereby
creating sonogramic), a form of diagnostic imaging used in medicine.
Fluid
dynamics and resonant conditions
All else
being equal, increasing the volume of the fuel-air mixture (energy input) flowing
through an internal combustion engine (ICE) increases power and torque (energy
output). This can be done with an
external device such as a supercharger, or resonance can be created in the induction
system by designing a passage which uses the physics of fluid dynamics to
increase pressure in specific spaces.
Obviously uninvolved in the engineering, Chrysler’s marketing people
claimed in 1960 that the Sonoramic was new technology but for many years the principle had been used in
racing engines, the mathematical equations determining acoustics &
resonance having been published by German physicist and physician Hermann
Ludwig Ferdinand von Helmholtz (1821–1894) in a scientific paper published in 1863. Indeed, the concept had before been used on
road cars but always in a discrete manner; what Chrysler did in 1959 with
the long-tube ram-runners was make a dramatic fashion statement in designer
colors.
Essentially, the Sonoramic
is an implementation of Sir Isaac Newton's (1642–1727) first law of motion,
more commonly known as the law of inertia: “An object at rest tends to stay
at rest and an object in motion tends to stay in motion” and it’s the
second part which Sonoramic exploited. During
the intake cycle of an engine, the fuel-air mix flows through the intake
manifold, past the intake valve, and into the cylinder, then the intake valve
shuts. At that point, the law of inertia
comes into play: Because the air was in motion, it wants to stay in motion but
can’t because the valve is shut so it piles up against the valve with something
of a concertina effect. With one piece
of air piling up on the next, the air becomes compressed and this compressed
air has to go somewhere so it turns around and flows back through the intake
manifold in the form of a pressure wave.
This pressure wave bounces back and forth in the runner and if it
arrives back at the intake valve when the valve opens, it’s drawn into the
engine. This bouncing pressure wave of
air and the proper arrival time at the intake valve creates a low-pressure form
of supercharging but for this to be achieved all variables have to be aligned
so the pressure wave arrives at the intake valve at the right time. This combination of synchronized events is known as the "resonant conditions".
Most of the Sonoramics produced were
long-tubes with a tuned internal-length of thirty inches (760mm), generating
prodigious quantities of mid-range torque, ideal for overtaking under highway
conditions. These characteristics were
ideal for road cars but also built were a small number of the so-called
short-tube Sonoramics, a somewhat misleading term because they shared the
external dimensions of the standard devices, the difference being that only a fifteen-inch
(380mm) length of the internal passages were resonance-tuned and this, at the expense
of mid-range torque, produced much more power high in the rev-range making them
more suitable for competition. Used by
Chrysler to set a number of speed records, these were the most charismatic of
the breed and a handful were built with manual gearboxes. At auction, in November 2010, the sole 1960 Chrysler
300F short-tube Sonoramic convertible with the Pont-a-Mousson 4-speed gearbox,
sold for US$437,250.
The first four
generations of the 300 letter series had used increasingly larger versions of
the Hemi V8 and the 1958 300D (with a 392 V8) even offered the
novelty of a very expensive fuel-injection option but, unlike the mechanical
systems offered by Mercedes-Benz, Chevrolet and a handful of others, the Bendix
"Electrojector" system used a rudimentary computer which proved
unreliable and most were returned to the dealer to be retro-fitted with carburettors. The Hemi, heavy and
expensive to produce, was in 1959’s 300E replaced by the larger capacity, wedge-head 413
which matched it for power but lacked the mystique, something substantially
restored in 1960 when the 300F debuted with the sexy Sonoramic. Ram Induction today is common, although
contemporary designs, integrated with fuel-injection systems, are not as
photogenic as the original Sonoramics.
As well as raw aluminium, the tubes were available in the designer
colors of the time, red, gold and blue; red ones are thought most cool.
Chrysler’s interest in ram tuning was an outgrowth of the desire to exploit the findings of research undertaken during the war developing very high-performance piston engines for fighter aircraft. This had culminated in the XI-2220, a 2,220 cubic inch (36.4 litre) V16 aero-engine which, rated at 2450 horsepower, was tested in a Republic P-47 Thunderbolt, an appropriate platform given that the P47 was then the biggest, heaviest single-engined fighter ever to enter service (among piston-engined aircraft it still is). Although the indications were that close to 4000 horsepower was achievable (at least for short durations), with the advent of the jet engine the days of the big piston-engined fighters were nearly done. The V16 project was cancelled, a fate suffered also by the other outstanding big aero-engine of that last generation: the Napier-Sabre H24.
The lessons learned however would be applied on
the ground instead of in the skies because although big capacity piston engines
had mostly been rendered obsolete for aircraft, a few generations of some just a bit smaller were
about to start roaming American roads.
The cars and their engines would be like nothing before seen, Chrysler
adopting for their new 331 cubic inch (5.4 litre) V8 in 1951 the V16’s hemispherical combustion chambers, a feature it would use for most of that
decade and the next and such was the aura of the name that it’s used still,
even if things are now a bit less hemispherical than before.
The new Hemi V8 had obvious performance potential and
the engineers experimented with the tuned-length induction system used on the
V16 before the final supercharger/turbocharger combination was adopted. So successful was the ram-tuned engine (named
A-311) that attempts were made to contest the 1952 Indianapolis 500 but the
race’s sanctioning body understood the implications the remarkable new
powerplant would have on their carefully-curated ecosystem of owners and
sponsors and declared it didn’t comply with the rules, even tweaking them a bit to ensure it never would.
The research however continued and, although it’s not clear to what extent their efforts received factory-support, in the late 1950s some young engineers formed the drag racing-focused Ramchargers Club using, somewhat improbably, a 1949 Plymouth business coupe fitted with a particularly extravagant implementation of the technology, a surrealistically tall intake manifold, a device built for dynamometer testing and never intended for a moving vehicle. They dubbed the Plymouth "High & Mighty". Bizarre it may have looked but the cartoon-like Plymouth achieved results which vindicated the approach and the system was introduced on 1960 Plymouths, Dodges and Chryslers, the highest evolution of Sonoramic offered on the Chrysler 300 letter series cars until 1964. Interestingly, while it was only Plymouth which used the Sonoramic name, Dodge labelling the system D-500 Ram Induction and Chrysler simply Ram Induction, all of them are commonly referred to as Sonoramics.
Not content with applying the science of fluid dynamics only to the induction system, the Ramchargers used it also for the exhaust headers. Rather than additional power, the commendably juvenile quest was for noise, the exaggerated, trumpet-like tubes using the megaphone principle which increases volume by raising acoustic impedance. The desired result was achieved and although there's no record of anyone with a decibel-meter taking a reading, the old Plymouth was said to be spectacularly loud. Megaphone exhausts were subsequently banned.
Chrysler didn’t restrict the ram induction idea to the big-block V8s, using it also on the short-lived (1960-1962) Hyper Pak performance option for the both 170 cubic inch (2.8 litre, 1959-1969) and 225 cubic inch (3.7 litre, 1987-2000) versions of their Slant Six, the engineers taking advantage of the space afforded by the angled block to permit the curvaceous intake runners nearly to fill the engine bay. The Hyper Pak wasn't seen in showrooms but was available as an over-the-counter kit (literally a cardboard box containing all necessary parts) from Dodge & Plymouth spare parts departments and its life was limited because it became a victim of its own success. Although less suitable for street use because it turned the mild-mannered straight-six into something at its best at full throttle, in the race events for which it was eligible it proved unbeatable, dominating the competition for two years, compelling the sanctioning body cancel the series.
Although it was the longer lived 225 version which gained the Slant Six its stellar reputation for durability and the ease with which additional power could be extracted, there's always been a following for the short-stroke 170 because of its European-like willingness to rev, the characteristics of the over-square engine (unique among the slant-six's three displacements (170-198-225)) unusually lively for a US straight-six. Despite some aspects of the specification being modest (there were only four main bearings although they were the beefy units used in the 426 cubic inch Street Hemi V8), for much of its life it used a tough forged steel crankshaft and high-speed tolerant solid valve lifters and was a famously robust engine. Despite that, after the Hyper Pak affair, Chrysler showed little interest in any performance potential, knowing the US preference for V8s, something which doomed also Pontiac's short-lived single overhead camshaft (SOHC) straight-six (1966-1969). A version of the 225 with a two-barrel carburetor (rated at 160 horsepower, an increase of 15 over the standard unit) was offered in some non-North American markets where V8 sales were not dominant and it proved very popular in South Africa, Australia, New Zealand and Central & South America but only when tighter US emission regulations forced its adoption did a 225 with a two barrel carburetor appear in the home market, installed to restore power losses rather than seek gains.
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