HEMI Heritage

The heart of the matter, 1962-1963

Geoff Stunkard - April 24, 2014 02:51 PM


This early Hemi cutaway in the Garlits museum engine room shows the basic configuration of the combustion chamber. Note the cylinder thickness at the lower edge, and the shallow block skirt between the cylinder end and the oil pan lip.

Photo provided by Geoff Stunkard

This interior shot of the lifter valley shows the cast-in fifth bolt location, and the cast-in tubes for the angled pushrods.

Photo provided by Geoff Stunkard

The 1966 Street Hemi cutaway from the Garlits museum shows the angled rocker gear, thick-cast walls, and deep skirt with crossbolted main caps.

Photo provided by Geoff Stunkard

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     The success of the 426 Hemi at the 1964 Daytona has been recounted many times. To get to the fabled February event in Florida, engineers at Chrysler doubled-down on time and effort to take the RB engine block design that been created for the wedge-style cylinder head and adopt a redesigned version of their earlier hemispherical cylinder head to that block. While it may sound like an elementary process, it was actually a combination of talent, effort, experience and sheer exact timing that made the 426 Hemi engine a dominant winner rather than a mere footnote in racing history.
      The first-generation Hemi engine had also been the first V-8 Chrysler offered in a production car. Testing started prior to the Second World War. Engineering work led by James Zeder and William Drinkard had determined that the hemispherical combustion chamber offered optimal combustion characteristics. Zeder and Drinkard were able to convince the somewhat stoic management team at Chrysler headquarters that it was the way to go. Testing commenced in 1948 and the Chrysler FirePower arrived in the 1951 model line.
      It would begin a lineage of hot Chrysler power development both in and out of Detroit. The Hemi was quickly heralded as a trendsetter. The powers-that-be at Indianapolis wanted OEM production engines to make attempts at the 500, but changed the rules instead after the Chrysler design showed vast superiority. When engineer Bob Rodger came up with the idea of the Chrysler 300 in 1955, featuring 300 horsepower from a 331-inch design, the musclecar marketing concept was born.
      By the late 1950s, hot rodders like Don Garlits and Emory Cook found ways to get the engine to burn large doses of nitromethane for fuel. A group of young Chrysler engineers, who called themselves the Ramchargers, put one together as a club project in a 1949 Plymouth business coupe. Among them was an engine development specialist named Tom Hoover.The passenger car Hemi engine itself though was discontinued in 1958 for a more economical engine using a wedge-type head design.
      When Lynn Townsend became Chrysler president in 1962, he realized the company needed an image change. Townsend saw there would be big benefits to creating a winning image around the Daytona 500, giving Chief Engineer Robert Rarey and his assistant William Weertman the job of figuring out how to do this. Bob Cahill and Jack Charipar helped push the program through the executive side of things.
      Hoover was familiar with the early Hemi. He also had been involved with the Max Wedge drag racing program, and understood the issue was getting RPM and breathing room into the already-designed RB engine block. There were a couple of problems to be dealt with.  With the way the head was to be bolted down to the block, the fifth bolt on each cylinder was in conflict with the intake port and pushrod. A more critical issue was the hemispherical chamber and its associated valve rocker gear. If set up on a 90-degree position, it would be too wide for installation into the currently-designed unibody vehicles.
      A talented draftsman and designer named Frank Bailk got to work. He came up with a plan that brought the fifth bolt in from beneath, torqued upward into the head through a thick bolt support that was cast into the lifter valley. He then took the Hemi rocker arm and angled it to a 58-degree offset, allowing for both a shorter rocker arm and moving the pushrod away from conflict with the fifth head bolt’s location. Cast-in tubular openings for the pushrods were added to the lifter valley as well; these were angled to help maintain the valvetrain geometry. The rockers remained shaft-mounted, and the valve angles retained the same basic configuration as had been optimized the first-gen Hemi. Turning to the block itself, already a deep-skirt design which was inherently stronger than the earlier version of the Hemi, Bialk added crossbolted main caps for endurance.
      What had not been fully understood, however, was the weight of the new rod and domed piston in relation to thrust. It became evident that the loading by those heavy swinging parts was capable of cracking the right hand cylinder walls. The testing, which replicated real-world race conditions, proved a flat-out run of 500 miles was not going to happen. As the piston’s design was finalized by this point, the issue turned to the foundry in Indianapolis where the blocks were being poured. Oh, and it was already January 28, 1964…Daytona was 26 days away.

(Geoff Stunkard, former editor of Mopar magazines, is presently writing an overview history of Chrysler’s Race Hemi engine for Cartech books to released in 2015. He will be highlighting Hemi heritage on this 50th Anniversary for Cars & Parts throughout 2014.)