It all started in 1951 when Chrysler introduced a new line of V8 engines with an usual shape to their cylinder head combustion chambers. Unlike previous designs, these new Chrysler engines had “heads” that were cast in the shape of a dome, or hemisphere. Enthusiasts soon started calling the new engines “Hemis” and the name stuck. Later in the 50s actually became a brand name trademarked by Chrysler Corporation.
Whats unique about the engine is that the hemispherical combustion chamber design allowed engineers to place the intake and exhaust valves on opposite sides of the combustion chamber. This lent itself to large valve surface areas and robust head cooling passages all of which made for a much cooler running engine. Because the engine was so thermally-efficient, higher compression ratios could be designed resulting in an engine that also produced lots of horsepower and torque.
The Hemi engine really came into its own in the mid-1950s During this time Chrysler Corporation models such as Chrysler (with the FirePower Hemi Engine), DeSoto (with the FireDome Hemi Engine), Dodge (with the Red Ram Hemi Engine) adopted the design. With fuel costs at historic lows, the automotive public loved cars with the Hemi engines because of their high horsepower. In fact, when researching this article, www.chryslerofculpeper.net told us that the stock Chrysler 426 HEMI Engine in 1964 was actually so powerful that it was initially banned from NASCAR races as “unfair competition”.
Complexity = cost
The downside to the traditional Hemi design was complexity. From the beginning, Hemi engines have had two rocker shafts per head and a very complicated valve train. While this lent itself to engines that delivered superior performance, it also cost Chrysler a lot more money to make them. Unfortunately, this would set the stage for the phasing out of the original Hemi engine design and reinstatement of the original, cheaper wedge head designs.
The brand lives on
Today, we see many vehicles that bear the Hemi designation but in most cases this a branding decision. While some of today’s Hemi’s have actual hemispherical heads, most have polyspherical (multiple curves) heads or are simple wedge heads. The original Hemi may be a thing of the past but it’s legacy lives on.