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Early Hemi Motor

The Golden Age of the Chrysler Hemi

By Crystal Stern - Hemicat



Salt crackles under the wheels of the car as it rolls down the dry lake bed flaunting the excesses of it’s Virgil Exner styling, the powerful Hemi roars under the hood as the car flies upon the sand to a new world speed record.  When it comes to vintage racing what is more of an icon than the Hemi?  The Chrysler Hemi revolutionized the world of racing, and established Chrysler as the king of performance.  Big horsepower was suddenly available to the masses, leading to the golden age of the quintessential American sport- drag racing.


Hemi drawings  - Click for full size


The early Hemi was produced by Chrysler from 1951 to 1958.  It shared nothing with the newer 426 Hemi except the basic valve arrangement and the distinctive hemi spark plugs sticking up through the valve covers. They can be easily identified from the 426 Hemi because the early Hemi has the distributor located at the rear of the engine whereas the 426 has the distributor at the front.  The original Hemi created by Chrysler was called “The Double Rocker” engine, not until the 426 did “Hemi” become the official name, now a trademark of Daimler Chrysler.  However, as much as us Mopar freaks would like to think so, Chrysler was not the innovator of the hemi engine.


The first hemi engines built were by Chelsea Mfg. Co. in Chelsea, Michigan in 1903.  The Chelsea Welch had a two cylinder engine with overhead valves and hemispherical combustion chambers and put out 20hp.  Chelsea continued to build Hemis until 1909 when the company was acquired by General Motors.


A Peugeot Grand Prix car running a hemi in 1912 gave Europe "Hemi Fever". The Peugeot was powered by a 3 liter engine with an overhead camshaft and four valves making it a pent-roof chamber actually.  By the 1920’s a hemispherical combustion chamber was the norm in racing engines.  Hemi heads feature intake and exhaust valves set at opposing angles in the head creating a hemispherical combustion chamber.  This design makes for phenomenal intake and exhaust flow, making it easy to build horsepower.


Chrysler began research on the hemispherical combustion chamber in the 1930’s.  During WWII Chrysler developed the inverted V-16 aircraft engine which was a Hemi and continued research through the end of the war in 1945 when the development of Hemi aircraft and tank engines was halted.  The engineers had learned a good bit about the advantages of the Hemi head and wanted to apply that knowledge to create more power for their passenger cars, but the components to build Hemi heads were too expensive and complex because of a complicated valve train layout.


Zora Arkus-Duntov was working under contract with Ford in the mid-1940s to design an overhead valve conversion for flatheads to be used in trucks.  These heads, sold as the Ardun conversion as speed parts, were very similar to the Chrysler FirePower V-8 in their valve train design, so much that some people infer that Chrysler borrowed upon the design in the creation of the early Hemi, but more than likely it was simply coincidental.


Chrysler engineers experimented with valve train designs of Hemi heads on their L-head six motor calling it the A161.  It had a pushrod type of valve train rather than the overhead cams that most of the European Hemi designs used.  The Hemi six was used extensively in Australia throughout the 60’s and 70’s.  The 265ci Hemi six was designed to be used in trucks, but the idea was abandoned in the U.S. in favor of the V-8 design.  In Australia the regular production Hemi six had 203hp and 262 ft-lbs of torque.


The major difference between the Chrysler Hemi and other makes is the means of running the valve train, dual overhead cam, overhead cam, or pushrods.  Chrysler used adjustable pushrods and offset rockers to create a Hemi engine that was financially feasible as a production engine, and also allowed more valve lift creating greater performance potential.  The milder motors came with hydraulic lifters, and the higher output engines came with solid lifters.


The performance advantages of the Hemi lie in its ability to burn fuel evenly.  With the spark plug centered in the cylinder the flame of combustion travels at an even pace, burning all the fuel and pushing down on the piston with even pressure.  In fact, Chrysler engineers were seeking fuel economy and engine durability rather than high output when they designed the Hemi, pretty funny when you consider that the phrase, “passes everything but the gas station” was originally coined for the Chrysler 300.


The Chrysler FirePower Hemi was first introduced in 1951 as a 331 cubic inch V-8, weighing in at almost a thousand pounds dry, with a then unbelievable 180 horsepower at 4000 rpm.  This behemoth came with a forged steel crank and big valves, a 1.81 intake and 1.5 exhaust, to give it unbeatable flow.  Unusual to these first 331ci Hemis were the cast in the block bell housing flange, which was discontinued in 1954.  This elephant was only the start with the cubes getting pushed up to 354, then the ultimate 392 Hemi, putting out up to 390 horsepower straight from the dealer.  As “Big Daddy” Don Garlits explained, “I’ll never forget my first introduction to the Chrysler Hemi.  My friend and I were driving down a street in Tampa, Florida, and we looked in the window of a Chrysler dealership.  They had a big sign that read, ‘V-8, 180 horsepower.’ We thought it was a mistake, it should be 108 horsepower.  But it was not a mistake.”


Most of the Chrysler brands jumped on the bandwagon, with DeSoto creating its FireDome and Dodge with its Red Ram.  The DeSoto FireDome was introduced in 1952 and had a displacement of 276 cubic inches, and the Red Ram was unveiled by Dodge the next year as the smallest of the family with only 241 cubes.  Plymouth didn’t offer a Hemi powered car until the advent of the 426, but it was common in the 50’s for hot rodders to shoebox a Hemi motor into a lightweight Plymouth body.


The Chrysler Hemi quickly developed a speed demon reputation in racing.  Briggs Cunningham in 1951 used the Hemi engine for his Le Mans Race car.  In 1952 Kurtis Kraft tested a special Hemi in his Indy Roadster; the Hemi was banned by racing officials for being too fast.  Lee Petty won 5 NASCAR races and finished second in points in 1953


In the mid 1950’s Chrysler decided to shake up it’s conservative image with the introduction of the “300.”  The 1955 Chrysler 300 had a 331ci Hemi with two four barrel carbs, a full race cam, solid lifters, bigger valves (1.94 intake and 1.75 exhaust) and dual exhaust system. The namesake of the C-300 came from the incredible 300 horsepower the Hemi put out, the only production vehicle that came close was the Cadillac Eldorado with 270 horsepower in a vehicle that weighed a thousand pounds more!  The C-300 did 127.58 mph in the Flying Mile and averaged 92 mph in the Daytona Grand National stock car race, sealing its fate as a legendary machine.


Each year Chrysler continued to offer more horsepower making options as the big three automakers fought an all out war for the fastest luxury automobile.  In 1956 the 300B came with the 354 cube Hemi V8 that generated 340 hp, and an optional 355 hp version.  The high output model came with 10:1 compression and a three inch exhaust system.  The 300B hit over 140 mph in the Flying Mile and Buck Baker won the NASCAR grand championship in a Hemi-powered race car, earning 14 wins during the 1956 season, setting the world speed record in Daytona Beach at 133.9 mph. 


In 1957, the ultimate horsepower was upped to 390 from the new 392ci Hemi V8, which featured a compression ratio of 10:1 and a full race cam, however this monster was only available as part of a wider package, titled the “Optional Chassis and Engine Package.”


This performance option included manual steering, a four-speed transmission, a limited-slip differential and a heavy duty clutch.  This was never intended as a street friendly package and shows how seriously Chrysler was taking its racing capabilities.  The 300C could accelerate from 0-60 in eight seconds and reached a top speed of 145 mph in Chrysler tests.


Old style Hemis were offered in 2-Bbl, 4-Bbl, and dual 4-Bbl versions.  The 1958 dual quad 392 FirePower Hemi came with a standard motor producing 380hp and an optional Electrojector fuel injection system.  Developed in conjunction with Bendix, this $400 EFI system delivered an extra 10 horsepower and included a 40-amp generator, an electric fuel pump and an electronic modulator.  However computer technology at the time was not up to the challenge and the system was troublesome therefore Chrysler announced a recall.  Of the 16 cars sold with this fuel delivery system all but one were converted to the ordinary, but less high maintenance, dual carburetor set up.  Performance was still world class with Norm Thatcher driving a 300D to a new Class E speed record at the Bonneville Salt Flats of 156.387 mph.


As successful as the Hemi-powered Chryslers had been, it was proving increasingly expensive to manufacture and Chrysler engineers felt they had taken the Hemi engine as far as they could.  1958 was the last year the legendary Hemi would be featured in a 300, however the racing legend continued. “Big Daddy” Don Garlits broke the 180mph barrier for the quarter mile while campaigning in his “Swamp Rat” Hemi powered dragster in 1958, then in 1964 broke 200 mph.  The original “Ramcharger” debuted with a Hemi powered ’49 Plymouth running C/Altered class to win the NHRA Nationals in 1959.  The record for a 392 iron motor is 5.85 second quarter mile time at 239 mph and was set by “The Surfer” Jeff Diehl at Lion’s Dragstrip in 1972.


The Chrysler FirePower Hemi became the most sought after engine for drag racing applications, and even with the advent of the 426 hemi the FirePower to this day is used in nostalgia drag racing.  Tens of thousands of 392 Hemis were built in the 50’s and by the mid 60’s engine assemblies and parts were cheap and readily available.  The early Hemi has no interchangeable parts with the 426 Hemi.  Also because of the number of different early Hemis, interchangeability of parts between the various blocks is limited.  Since the engine’s haven’t been produced since 1958, replacing broken parts can be difficult, but since they are run in many nostalgia dragsters and funny cars some racing parts are available, especially for the 354 and 392 versions.


Hemi Chart - Click for full size


With the engine already being successful for many years in drag racing, even though the 426 Hemi came out and dominated the oval track scene, drag racers were in no rush to swap over.  The hemi inspired fear upon racers of other makes, making it the true king of motors.  Needless to say, the early Hemi will not be forgotten, especially with the new 5.7L small block Hemi continuing the legacy today.



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