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

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.

Mythical Monster

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.

Double-Tap Hemi

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.