The year was 1964. Throughout the first part of the decade now renown for its automotive performance heritage, Ford, General Motors, and Chrysler had battled for supremacy in the racing world. Daytona, Bonneville, and drag strips throughout the nation had been the sites of these skirmishes, and each manufacturer had its moment in the sun. However, the start of 1964 was to be different, indeed.
Engineers at the Chrysler Corporation had pulled out all the stops and revived the hemispherical combustion chamber design that had been part of the luxury passenger car line-up in the '50s. Now displacing 426 cubic inches, the engine would no longer be considered a modified player used primarily in nitro dragster racing-the factory had reworked the technology around the existing RB-block combination as a flat-out competition unit, suitable for all forms of racing.
Here are the new lightweight valvetrain components for the Hemi(r) cylinder head. The rock
As the battle for the new season got underway, it was obvious that this was the secret weapon Dodge and Plymouth racers had needed to settle the score once and for all. With NASCAR's Petty family, the Summers Brothers efforts on the salt flats, and dozens of victories in every drag racing sanctioning body, the legend of the Hemi was soon firmly established. Only changes to the rules kept it from total dominance of these series.
The Legend Lives On
Despite 35 years of history, little has tainted the reputation of a well-tuned 426 "elephant" motor. However, since all racing series and products live in a state of flux, in some ways the technology that dominated that '60s is no longer viable in the 21st century. Though the design continues to be the dominant factor in nitromethane-burning vehicles, it is now too big displacement-wise for NASCAR and is not a factor in Pro Stock racing, either. There are a number of reasons for that truth.
The shape of the Hemi piston and combustion chamber may work very well in applications under 8,000 rpm, but above that speed, a number of critical problems can occur.
First of all, the weight of the reciprocating parts themselves. To build a true hemispherical combustion chamber requires a piston forging that will automatically weigh more than a similar construction wedge-style piston simply because of the shape.
Another view of the rocker arms and stands. Since the aftermarket does a superb job in tur
What's more, that piston's movement will need to be timed properly to do two almost opposing tasks-fill the chamber to build significant compression while avoiding problems with valves hitting the piston's face. At lower rpm levels, valve timing is not as critical, but in the world of Pro Stock racing, there is no room for error. Indeed, the best engine designs are on such a ragged edge that valve timing is set so the valves will actually barely touch the piston on the intake stroke. The design inherently makes big compression incompatible with high-valve lifts.
Then there is the problem with the valvetrain itself. Those long rocker arms and shafts might have made the assembly of the engine simpler, but they are actually modified versions of the technology originally developed in the '50s. At high rpm, there is a whole lot of flexing and bending of these parts. Also, they are not only heavy, but they contain some "unique" geometry (pushrod angles, etc.) where, again, high rpm efficiency suffers.
The Next Generation
So, it was within this environment that the design for the new-generation Hemi began. The photos you see here were taken at the Nickens Brothers Racing Engines shop near Houston soon after the initial pulls on their first Hemi motor were done. David Nickens, who is involved not only in this design but a small-block Pro Stock Truck program as well, graciously allowed Mopar Muscle to see some of the hardware used in making the new motor. In the captions, you will get a first look at the parts that are almost assured to put Chrysler's Pro Stock program back on the map.
This is the partly-machined Hemi cylinder head casting as seen from the exhaust side. As y
Main caps are created from high-tensile aluminum alloy to keep weight down and are cross-b
You are looking at the bottom end of the second-ever new Hemi motor put together at the Ni
Perhaps one of the most telling items of the amount of thought that went into the motor is
Created from a steel forging by Steve Lowe at LSM, this view shows how far the lifter posi