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The Plymouth Sonoramic Commando Engine

based on Joe Godec's article in the Plymouth Bulletin.

Plymouth's long-standing reputation for reliability was no longer an asset in the mid-1950s; people wanted racier, more stylish cars. Sales in 1954 tanked, as buyers defected to Chevrolet and Ford in droves, to get long, low, and sleek cars with V8 engines and fully automatic transmissions. V8s were hot, and many cars had V8 badges to show off; but Plymouth stuck with a single, outdated flathead six.

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The 1951 Chryslers had a V8 - an efficient hemispherical-head design, as powerful as it was expensive to build; it was also heavy. The company developed a polyspherical-head alternative, which still was not practical for Plymouth volumes (or prices); they used it on the 1955-57 Plymouths, but they were too expensive and slow for their mass-market brand.

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Engineers soon realized, in their testing, that a simple wedge head was almost as efficient as the poly, but far easier and faster to make, and the 1958 Chrysler Corporation cars could have their first wedge-head "B" engine, in 350 or 361 cubic inch forms. The first practical V8 for Plymouth had been found, and dubbed "Golden Commando."

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The B engines went through numerous expansions, for ever increasing displacements; but the ram induction system was far sexier. Chrysler engineers had discovered a powerful "supercharging" effect that could be altered by changing the length of the intake tubes; essentially, the air bouncing off the closed valves could then push more air into the valves when they opened, at certain engine-revolution (rpm) ranges, and changing the length of the intake manifold tubes would create extra power for the engine within different ranges. Basic research had started many years earlier, in the 1940s; only now did a final product hit the streets (one which is still used today, in different forms).

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The 1959 cars revealed a new "cross-ram" design; engineers had chosen 30 inches as the perfect length, and to make the tubes actually fit under the hood, they put the carburetors on opposite sides of the engine from the ones they fed, and pushed the air across the top of the engine. Each manifold had a four-barreled Carter AFB.

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Because they figured owners would raise the hood a lot, they colored the ram tubes, valve covers, and air cleaners in gold, and the rest of the engine in red. Carburetor balance was first adjusted with ball-and-socket rods, later with slotted adjusting links.

Some later engines had the same tubes, but with passages only 15 inches long. The shorter the passage, the higher the rpm range they boosted. The 30-inch tubes were designed for a midrange boost - for instant passing power, rather than for racing.

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Plymouth's brand name "SonoRamic Commando" was attached to these engines - "Sono" from the sound-wave-like wave of compressed air, which pushed more air into the valve than would otherwise be possible; and Ram(ic), because that compressed air started when the valve closed, and the air/fuel mixture hit it and bounced off. (Dodge sold one as the D-500).

The first Plymouth SonoRamic Commando was a 361 cubic inch engine, rated at 310 horsepower and 435 pound-feet of torque (Dodge's had slightly higher ratings). By comparison, the same engine in Golden Commando form was rated at just 395 pound-feet - a difference of around 10%.

It cost $389, nearly 20% the price of a low-end Plymouth. It was only supposed to be sold with an automatic, but some may have been built with three-speed manuals. Proud owners of 1960-61 Plymouths with the engine had badges proclaiming the fact - on both sides, up front, in 1960 cars; and on the rear deck lid, one side, in the 1961s. The specific position varied.

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Later in the first model year, Chrysler put the induction package onto the 383, a similar engine; this boosted horsepower to 330 and torque to 460 pound-feet. Dodge's version was rated at 345 hp and DeSoto's at 350 hp.

1961 buyers could no longer buy the 361 SonoRamic Commando, but the 383 was still around, and now the 413 joined it, with 375 horsepower (400 in the rare short-tube version).

The SonoRamic Commando didn't make it out of 1961, except for some rare cases, such as the 300 letter cars. Chrysler downsized all their 1962 cars, thinking GM was doing the same; and now the manifolds didn't fit.

The design was meant for power, not ease of use; fuel usage was quite high and spark plug changes, at the time done at least once a year, required taking the wheels off and going in from underneath. When cold, the engine was prone to flooding because fuel puddled in the chambers underneath the carburetors.

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The most famous SonoRamic Commandos may have been driven by Al Eckstrand, who won the Super Stock Automatic class at the national NHRA meet in Detroit, beating a "Super Duty" Pontiac with 14.51 seconds at 97.82 mph.

The Sonoramic Commando is very rare today, with few made during their short run, and few of those surviving.

With help from Daven Anderson, Pete McNicholl, and Curtis Redgap.


Chrysler 1904-2018

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