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Origin of the Mopar Hemi engine, Ardun Heads, and Riley cars

1966 chrysler street hemi enginesThe question of who invented the hemispherical combustion chamber is rather a silly way to waste time. Chrysler didn't, and never claimed otherwise. But Zora Arkus-Duntov didn't either, and I don't believe he ever claimed to.

The advantage of the hemi layout, with valves angled away from each other, lies with increased valve size, and greatly enhanced porting.

In The Grand Prix Car Volume 1 by Lawrence Pomeroy, the first mention of angled valves and overhead camshafts is in his description of the 1912 3 liter Peugeot Grand Prix car, designed by a Frenchman named Henri. This was not a hemispherical chamber, it had four valves in what's known as a pent-roof chamber. So it's a level above the hemi. Hence, the inventor of the hemi, if he exists, came up with a way to reduce the potential of the overhead cam, multiple valve design.

Numerous other makes copied Peugeot and by the 1920s angled valves in crossflow heads were the norm in racing engines, both in Europe and the United States. Delage, Ballot, Bugatti, Chevrolet, Deusenberg, Frontenac, and Miller, to name just a few, were all either hemis or had pent-roof chambers with four valves per cylinder. More recent marques include Jaguar, Aston-Martin, Coventry-Climax, Coswoth, Ferrari, and Maserati.

The major difference between makes is the means of running the valve train; dual overhead camshafts, a single overhead camshaft, or pushrods. Chrysler chose pushrods and they worked amazingly well. By the way, does anyone know what the original hemis were called by Chrysler? "The Double Rocker." It wasn't til the 426 that "Hemi" became standard. And HEMI is now a registered trademark of Chrysler.

Chrysler sold Ford V-8s with modified Ardun head kits in Brazil

Chrysler never claimed to have the first mass-produced hemi, either. I don’t know who was first, but BMW had their 2.8 liter inline six cylinder engine in the 328 sports roadster in the mid-1930s. This engine had an in-block camshaft with 18 pushrods, 18 rockers, and two rocker shafts. The extra pushrods were horizontal, crossing the cylinder head to operate the exhaust valves. Despite this Rube Goldberg setup, the engine was good for its time. It was manufactured under license by Bristol in the UK. In the 1950s, an AC Ace sports car with Bristol engine was a winning combination in production sports car racing both here and abroad. For those of you too young to remember, it was the AC Ace sports car which became the Shelby Cobra.

Anyone who has visited the Walter P. Chrysler Museum in Auburn Hills, MI has seen the first Chrysler Hemi, in the form of the XIV-2220 inverted V-16 aircraft engine developed by Chrysler during World War II. The engineers who worked on the project gained valuable experience which they later applied to further experiments with hemi heads on corporate 6 cylinder engines. I imagine more than one was aware of the existence of the Ardun heads for Ford engines [see below]. And if there were features which applied to the new engine design, I hope they adapted them. This work lead to the 1951 Firepower V-8 of 331 displacement. And to the 1952 Desoto Firedome V-8 of 276 cid. And then to the 1954 Dodge Ram V-8 of 241 cid; all were hemis.

What Chrysler could claim as a record would be the mass production of more hemi-type engines than anyone. Period.

In 1951, James C. Zeder wrote an article for Motor Trend which was reproduced with permission in the WPC News. He referred to numerous past designs, including the Ardun heads and many other predecessors of the Chrysler Hemi. One very early engine he referred to was the 1904 Belgian Pipe Company twin-cam powerplant, adapted for pushrods; he criticized this engine, though, for the poor airflow leading up the heads, with sharp bends. The spark plug was in the center for “short, uniform flame travel.” He called the 1927 Delage engine a “thoroughbred masterpiece” with nearly 2 hp per cubic inch (remember, the best muscle car engines could achieved one horsepower per cubic inch as sold); the air was unobstructed. However, its dual overhead cams were expensive and “often temperamental.” 

Zeder mentioned the Bristol 328 engine, based on a BMW design, using a single cam with pushrods; the Lea-Francis, with twin cams and pushrods (to avoid having cams in the head), noting that the layout was used by Riley; and noted that “Chrysler is the first manufacturer to make the high-output, high-economy, hemispherical combustion chamber available to the American public in true mass production.” The Chrysler engine also used pushrods, with self-adjusting hydraulic tappets to compensate for variations in pushrod length due to temmperature changes.

More to the point of this page, Zeder noted the Ardun inclined overhead-valve heads, “designed to bring...the hemispherical combustion chamber to owners of some L-head V8 engines;” according to Zeder, this increased output from 100 hp all the way to 175 hp, using the 7.1:1 compression ratio. He called them “building engines the right, but costly way.”

I did a little bit of research and the earliest "hemi" I can find is the 1903 Welch, built by Chelsea Mfg. Co., Chelsea, Michigan. It had a 20-hp, two-cylinder engine with overhead valves and hemispherical combustion chambers. The company moved to Pontiac, Michigan in 1904 and began producing larger cars with 36-hp four cylinder engines, still with overhead valves and hemi-heads. The 1906 engine had a 4.5" stroke and 5" bore with a single overhead camshaft and had one of the first water pumps driven by the fan belt.

The 1906 model also had an adjustable steering column permitting the driver to move the steering wheel up or down the column as needed. In addition to the four cylinder engine, Welch also built a 75hp six-cylinder engine with overhead valves, hemi-heads and a single overhead camshaft.

In 1909 the company was acquired by General Motors Company and set up a plant in Detroit to build the Welch-Detroit, with A.B.C. Hardy as General Manager. In 1911 the powers that be at G.M.ordered the machinery from the Welch plants in Pontiac and Detroit moved to the Rainier Motor Car Co. plant in Saginaw, Michigan. The Rainier Motor Car Co. was formed in 1905 and acquired by General Motors in 1909 or 1910.

The result was the Marquette (not connected to the later Buick-built Marquette). The new firm became the Marquette Motor Co., and this first Marquette used a four cylinder engine with a T-head sidevalve arrangement. No more hemis or overhead cams. The Marquette lasted one year.

Every item on the development of the hemi states that the Healey (Riley) engine had dual overhead camshafts. Went down to the library and dug up some old British repair books and checked up on the Riley. It did, indeeed, and two camshafts in the block with short pushrods. The reason for the short pushrods is that the camshafts are at the top of the block, just below the heads. With inline engines the camshaft is normally lower dow, just above the level of the crankshaft - a carryover from the side-valve engine undoubtedly. The high placement of the camshafts may give some the impression of being in the head.

There were two valve covers, one for each valve rocker shaft. Thus the spark plugs were mounted directly in the head without the need for spark plug tubes as used on Chrysler hemi engines. The Riley RM series was also sold in Canada, although very few were. The Riley Pathfinder used the same engine in a sedan body with more modern brakes and 4-wheel coil suspension. The styling of the 2005 Chrysler 300C reminds me of the Pathfinder. The later BMC-engined 1.5 and Farina body models are far more common.

Although the brakes on the RM series Riley were archaic, the front suspension was not. The 1946 Riley RM adopted torsion bars up front, with the adjuster at the rear (beneath the driver's feet) with the forward end mounted in the lower A arm. Eleven years later Mopar would adapt an identical version and call it Torsion-Aire.

Someone sent me a link to your Mopar-Ardun-mystery page and I found myself quoted, not unpleasantly.

I am glad to see some of your readers care for this ancient legend about a possible link twixt the 1947 Ardun and the 1951 Chrysler Hemi. It is undeniably true that there are a number of similarities.

One wag has stated that the 1951 Hemi merely consisted of a set of iron Ardun heads atop a 1949 Cadillac shortblock, and that today's NHRA Top Fuel Hemi is nothing more than a fully-developed Ardun!

No long dissertation at this time, but let me tell you of the discovery a couple years ago of my friend Mr. George Kudasch, 89, retired mechanical engineer, residing today in Connecticut. It came to light that in 1947 he was hired by Zora Arkus-Duntov to work as co-designer on the Ardun project at Ardun Mechanical Corporation in New York City.

After that project Mr. Kudasch went on to a very successful 30+ year career as a designer at Sikorsky Helicopters in CT, and received some patents in his own name.

He recalls very clearly that in later 1947 at AMC, Zora had some visitors from Chrysler Corporation and showed them what he was doing on his Ardun heads project.

Jay Fitzhugh touched on this story in an Ardun article last year in The Rodder’s Journal. George (b. 1916 in Russia) and the present writer worked on a long, in-depth interview about his life and escape from Germany to Switzerland in 1945, thence in 1947 to NYC; with the complete details of the design of the Ardun, etc. The very long George Kudasch Interview has just completed its four-parts publication in Bonneville Racing News.

Hemi and the Ardun heads

There is a story on the Internet which attributes the Chrysler Hemi engine's basic design to Ardun and Ford.

The "Hemi was borrowed" story:

The basic story is that the head was designed by Zora Arkus-Duntov, later a major force behind the Corvette. In the mid-1940s, he was working under contract with Ford to design an overhead valve conversion for flathead truck conversions; the heads were Hemis with two rows of rockers and plugs going through the rocker covers. They were offered by Ford to truck owners and by Ardun as racing hop-up kits. Some say (or impugn) that Chrysler borrowed from this design when setting up their first test mules.

"ArdunBill" wrote on the Internet, "Anthony Young in his book Hemi: History of the Chrysler Hemi V-8 Engine... interviewed surviving factory engineers and draftsmen about the origins of the design. The word "Ardun" appears nowhere in this book, but company engineers had long had a hemi design in mind, and by 1947 one of them (Moeller) was in the Engine Development Laboratory where, he says "We tested every engine in site (sic)". The company needed a major new engine for their postwar program, and knew of the OHV V-8 R&D at General Motors which became the '49 Olds and Cad units.

Moeller says the lab procured an English production car engine, a Healey with a long stroke hemi design, but high powered and very efficient. They were impressed with this. Subsequently a six-cylinder prototype Chrysler hemi was built, first with chain-driven DOHC, then a pushrod OHV rocker arm version (shown in the book). The latter was successful on road testing, and 'By 1948, Chrysler had a 330ci Hemi-head V-8 undergoing testing...' After successful testing the next version, the 331, was approved for production."

Another source wrote:

I asked Zora if Chrysler ever contacted him for a license or any consultancy on their heads. He said "No, the first I knew of Chrysler's V8 head design was in 1953, when I had gone to work for GM. One day I happened to see a poster on the wall with a cross-section drawing of the new Firepower V8. It was apparent that the head design was very close to mine of 1947. Standing there, I felt a great sense of pride that this huge corporation had followed my design and was making tens of thousands of successful engines with it. I didn't care to make an issue of it; engineers have always learned from and built upon earlier designs."

The more likely scenario:

Bill Watson wrote:

Just enough to be believable, but ...

The engine in the Healey was Riley's 2.5.-litre, hemi OHC in-line four. It was in production in the late 1930s and was used into the 1950s and was studied by a few manufacturers during its lifespan.

Not sure of the timeframe for the Ardun heads - will have to do more research on it. I suspect, though, the similarities between the Ardun and Firepower were more due to the cylinder bore size and block bore centres. With a given bore size the valves can only be up to a certain diameter. Any larger and they will hit the top of the block when then open.

By 1953 Chrysler had three hemi engines in production - Chrysler (Firepower), DeSoto (FireDome) and Dodge (Red Ram). And Zora knew nothing of these engines' heads until he went to work for General Motors in 1953? What rock was he hiding under since 1951? Every auto magazine and car show had the Chrysler Firepower hemi displayed and written about, complete with illustrations, when it was introduced in 1951. And magazines such as Motor Trend, Road & Track, Auto Topics, Popular Science, Popular Mechanics, and Mechanix Illustrated all made the introduction on their front covers. So how could he not know?

By the way, the last manufacturer to use the Ardun heads on the Ford flathead engine was Chrysler. In 1955 Simca purchased Chrysler of France for cash and stock, continuing to production the Vedette under the Simca name. In 1957 Chrysler purchased Ford's interest in Simca and gained a toehold in a European auto manufacturer. When Simca stopped production of the Vedette in 1963 (or so), Chrysler shipped the tooling for the car and engine to Brazil. By the late 1960s the Chrysler Esplanada, as the Simca Vedette was now called, apparently continued to use the Ford block, but with Ardun heads.

Patrick Clement wrote:

According to, “Hemi-headed engines were already common in Europe, mainly Grand Prix race engines, with the valves open[ed] and shut by twin overhead camshafts [DOHC]. Chrysler decided to adopt a different approach, instead of leaving its single five bearing camshaft in the vee of the bent eight [V-8], they chose to run adjustable pushrods up in a straight line to work short and long rocker arms, pivoted on parallel rocker shafts.

“James Zeder and Ev Moeller were on the team after the war that looked into the Hemi for Chrysler. They looked at a Healey engine with a Hemi-head and found it to be the most efficient design that they had seen. They built a head for a Chrysler six cylinder engine, and called the experimental unit the A161. It was tested in the real world in a car driven by the head of testing Wallace Zierer. It passed the test and by 1948 they had a 330 cubic engine called the A182, a V8 with Hemi-heads.”

Pete Hagenbuch wrote:

The Chrysler engine design and development people already knew more about the characteristics of Hemi type cylinder heads than Arkus-Duntov could. They had just recently gone through a long and rigorous program of bringing their fantastic V-16 liquid cooled aircraft engine to the threshold of production. Its output was reported as 2500 hp at the time the project was cancelled. Not bad for a new design still in development. Whatever help Chrysler engine people received from a study of Arkus-Duntov's, their own experience stood them in good shape for designing the worls's first mass produced V-8 engine with hemi heads and pushrod-actuated valve gear. That's my claim, not Chrysler's.

And finally...from Bill Thomas:

Former Chrysler engineer Peter Hagenbuch really tells it straight, and Bill Watson got it right too. The Welch, made in Chelsea, Michigan, was the first hemi.

Some clarification: the Cadillac and Olds development were really not the same program although both evolved from Kettering’s high-compression combustion research. These two engines both had wedge chambers. Olds developed a V-6 at about the same time as the V-8, which looked just like the V-8, only shorter. It never made production. A later experimental Olds V-6, circa 1961, used a Lancia V-6 “hemi” as a design study. We also tested and looked at the Willys in-line six truck engine which had a chain driven single overhead camshaft “hemi.” One of the later Olds V-6 engines is in the Reo Museum in Lansing, MI.

Note: the term "Hemi" is a registered trademark of Chrysler Corporation.

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