Historic. Legendary. Unbeatable. These—and many other descriptive words have been used to describe the 426 Hemi since its public introduction in 1964, but how did we get there?
It was December of 1962 when Lynn Townsend set the wheels in motion by authorizing the build of a new engine for the sole purpose of being a race-ready engine that could go to the 1964 Daytona 500—and win. For Willem Weertman and his crew at Highland Park, they had no time to come up with a plan. What they initially proposed, was a radical head design that would fit the already popular 440 block. The head that they envisioned would have a hemispherical-chamber design, and valves directly across from each other that would increase the power potential of the 440 exponentially. It was soon learned that using the 440 block presented more problems that needed overcome in such a short time, and it was going to be easier to build an all-new block. In March of 1963, the task of designing the heads was complete, and by December of that year, all of the ancillary parts were also ready, and testing could be done. On January 28, 1964, the 426 Hemi (Project A-846), roared to life in the dyno cell of Chrysler, beginning tests on the engine for a debut at the 1964 Daytona 500, and we all know how that went.
During the dyno testing that was being done to simulate what the engine would experience during the 500 miles at Daytona, a few problems arose. For some reason, the cylinders began cracking. This presented a huge problem, because the Dodge and Plymouth race teams would be rolling into Daytona in one week.
Willem Weertman and Larry Adams—the man in charge of race engine development, figured that if they make the cylinder bores thicker, the problem would be solved. This added material in the casting, meant that the sand cores being used to make the block would have to be modified by hand. This modification permitted more of the molten iron to flow into the cylinder wall area, and thus create thicker-wall cylinder bores.
With that fix in play, along came another disaster. During this revised casting process, a severe porosity issue presented itself. It was learned that the issue was caused by too much residual moisture in the sand cores. This was an easy fix, and all that was needed was a more thorough baking the sand cores before they were used to make the blocks.
Another issue that reared its ugly head at this time was residual stress in the blocks caused by the actual casting process. Residual stress is a stress formation found in a solid material, after the original cause of the stressing occurrence (in this case, the casting process), had ended. Unintended residual stress in a designed structure may cause it to fail prematurely. The metallurgists back at Chrysler came up with a plan to relieve it by annealing the blocks after the casting process once they had cooled. Once the blocks were cast, they would go into a furnace and get heated to 1,200 degrees Fahrenheit, and then they were slowly allowed to cool, and this relieved the stresses in the block.
When the 1964 Daytona race was over, the 426 Hemi (coded A-864), had placed 1st, 2nd, 3rd, and 4th. The total Chrysler domination of the Daytona race caused the Ford and Chevrolet camps to get their panties in a bunch, so for 1965, the sanctioning body decided to change their production rules. The mandate required that Chrysler make the Hemi available in production cars in order to comply with NASCAR regulations. This created an unbelievably huge problem for Chrysler, since at the time, the engine was only built for racing. They didn't feel that the engine was marketable in a standard production vehicle. What this did, was make the Hemi ineligible for competition when the 1965 NASCAR season was starting. Chrysler was on the outside looking in.
The 1965 hiatus, would eventually give them the necessary time to come up with a street-ready version of the Hemi. During the process, they had to create something that would be more durable for the open market. While Chrysler was out of NASCAR for 1965, they didn't completely forget racing, they did however change their focus. This was the year that Chrysler produced a special run of cars that were limited in their production numbers. They were identified by the first digits of their VIN number. If you had a Plymouth, R0 started your VIN, and W0 was used for Dodge. The Hemi engine package was called A-990.
It was reported that Willem Weertman stated that 210 examples (coded A-990) would be built. This was to begin on November 16, 1964, and finish on January 8, 1965. Each of the engines for these cars was assembled by hand at Chrysler's Highland Park facility. The engine spent hundreds of hours on the dyno, as engineers worked at refining the package following the Daytona 500 introduction. That time also saw the creation and production of aluminum cylinder heads (with redesigned intake runners for better fuel flow), and an ultra-light magnesium intake manifold supporting two Holley carburetors. Compression for this animal was set at 12.5:1, and a set of heavy—but high-flowing exhaust manifolds, funneled back toward a single muffler behind the rear axle. The sole purpose of the exhaust was to say the car had a street-legal exhaust, but as soon as the cars were delivered, that was one of the first things to get removed.
Taming the Elephant
It was in 1966 that Chrysler introduced the Street Hemi in its intermediate car line for general sales. This "mainstreaming" of the Hemi legitimized its use for NASCAR in 1966. That year, Chrysler offered the 426 Hemi in the Dodge Coronet and Charger, and the Plymouth camp stuffed it in Belvederes and Satellites. It didn't matter if it was a two-door or a four-door, the more vehicles it was offered with, the more legitimate it would be. Heck, even convertibles, and station wagons were eligible to get the Hemi engine. So NASCAR had no choice, they had to allow them to compete again. What they did do, was to limit the Hemi to 405 inches for the 1966 racing season.
The Hemi engine was very expensive to produce, and considering that most of the car base-models that had a Hemi as an available option cost around $3,000, the added $1,000 for the engine meant that mass orders didn't occur. There were many differences between the Hemi and the Wedge-head big-block. The Hemi included cross-bolted main bearing caps, and a different head-bolt pattern. There were also many differences between the Race Hemi and the Street Hemi. The Race Hemi featured a higher compression ratio, a more radical camshaft, a more performance-oriented intake and exhaust manifold. Some 1960s NASCAR and NHRA Hemi engines featured magnesium oil pans in an attempt to reduce the massive weight of the overall engine.
The Elephant Gets Brutal
Rated at 425 horsepower (yeah, right), the 1968 Super Stock Hemi featured the same goodies
In 1968, the Race Hemi mystique really took off with the creation of two all new specialty-built, limited-production cars. Opinions vary, but estimates of 80 Darts, and 50-70 Barracudas were built. These race-only Hemi powered cars featured a Hemi-specific four-speed, a narrowed Dana 60 with 4.88 gears, acid-dipped bumpers, lighter-than-stock Corning glass, fiberglass front fenders and hood, lightweight A100 van/truck bucket seats, no heater or radio, special Super Stock rear springs, disc front brakes, and most of all no warranty with the disclaimer "not intended for street use."
To keep the cost low, the Hemi came standard with cast-iron heads instead of aluminum. As one engineer explained, "For a thousand dollars less, the extra 70 pounds is not worth worrying about." The blocks were filled with 12.5:1 compression pistons, and fuel was ingested through a pair of Holley carburetors perched atop a lightweight magnesium intake. The cars were shipped with headers, and other features included deep-groove pulleys, a high-volume oil pump, and a roller timing-chain that reduced stretch and allowed more consistent engine timing. A dual points-breaker distributor worked with a Prestolite transistorized ignition and non-suppressed metal core wiring.
When Does a Hemi not Look Like a Hemi?
That question is easy to answer, when it's a ball stud Hemi. Known internally at Chrysler as A-279, it was intended to overcome the low-production process of the 426 Hemi. The ball-stud Hemi was intended to achieve a high-volume of manufacture at low cost, while still being a high performance engine. It is rumored that Chrysler hoped to replace three block and two head designs with the ball-stud design. Research shows that it was to be based on a low-deck block, and available in 400 and 440-inch displacements. While the new head design would cut weight and manufacturing cost, it also made it possible to fit the engine in more vehicles.
The initial design used the B-block head bolt-pattern, but it was learned that this interfered with exhaust flow. The design was later changed, but some tooling had already been completed. Although referred to as a Hemi, the head was not truly hemispherical. The intake valves were closer to the intake manifold, and the exhaust valves were closer to the exhaust ports. The staggered placement improved airflow by eliminating the sharp turns in the runners that are inherent with inline valve arrangements. It also had equally-spaced intake ports that were designed to achieve more consistent fuel distribution than Wedge heads.
The intake was to use a single Carter ThermoQuad, and dual four-barrels were never considered.
It's impossible to talk about the 426 Hemi, and not mention the dual over-head cam design that was toyed with. In 1964, the dual-overhead cam 426 Hemi was experimented with for the sole purpose of countering Ford's 427 SOHC. The problem arose when NASCAR ruled against allowing Ford's SOHC engine to compete. Because of that, there was no need for the overhead-cam Hemi testing to continue.
The DOHC Hemi was project A-925, and for the project to have been successful, it needed to be substantially more powerful than Ford's SOHC 427. Not only was more power a priority, but it still needed to be rugged enough to survive the rigors of racing—and conform to NASCAR's rules. Initially, two possibilities were considered. One design positioned the two cams between the heads in the intake valley area. With this design, the four valves at each cylinder would be operated by lifters, pushrods, and rockers. The second design was an engine that had aluminum heads, with two cams on each cylinder head, directly over the valve stems.
The latter design was believed to be the better choice, and was actually mocked up. The cams would be driven by a cogged belt, using external cam-drive wheels at the front of the heads. Since the cams were directly above the valves, this lowered the valvetrain mass, allowing the engine to rev higher with relative ease. One Chrysler DOHC Hemi still exists. It was rumored that the A-925 engine was only a ruse, and it was a completely nonfunctional engine that was only meant to persuade Bill France into banning Ford's SOHC engine.
In 1970, Chrysler engineers began testing with the theory of adding an extra spark plug to each cylinder. Adding the extra plug increased power by improving flame propagation (The spread of the flame in the combustion chamber, outward from the spark plug). There was small number of factory-spec twin-plug heads produced for the 426 Hemi. This 1970 press release photo shows a twin-plug head. There was actually a part number listed in the 1973 Mopar Performance catalog for a dual plug head. Part number P3690038 got you a dual-plug head for a Race Hemi.
The 426 Gets Modern
With the introduction of the 5.7 Hemi in 2003, and later the 6.1, a third generation of "Elephant" was born. Although 6.1 liters only equals 372 cubic inches, it is the base for an all-new 426 Hemi. By stroking the 6.1 with a 4.050-inch crankshaft, and using 6.125-inch connecting rods, the legendary 426 Hemi can continue life with an infusion of modern technology.