Hemi Heads Make 426 the Undisputed King of Muscle
Two syllables and four little letters carry the saga of a Muscle icon, and represent the peak of America’s home-grown, big-cube performance war of the 60s and 70s—a task all out of proportion for such a cute and friendly word. Perhaps a more fitting title would have been “Acrimonious Violator” or “Destructive Thunderfist”—yep, the 426 Hemi was a mean bastard with a friendly name, like if Carlos the Jackal had instead called himself “the Corgi”.
Hemispherical combustion chambers are nothing new—in fact, they pre-date the internal combustion engine itself by a few hundred years, seeing use in mortars and cannons for centuries. One has to look back another hundred years and change to 1901 for evidence of the pioneering use of this technology in gas engines, where it was first used in a boat motor, then shortly afterwards used in a handful of automotive applications—in short, the Hemi’s been around a lot longer than the NASCAR and domestic horsepower wars of the 60s and 70s that made it famous.
So what is that makes a round-roofed boom room so special? It all comes down to volumetric efficiency, i.e. how fast an engine is able to move a charge into and out of its cylinders. Normal “wedge” configuration engines, where the valves open and close side-by-side, tend to restrict air/fuel mixture flow into and out of the engine. Hemi heads, on the other hand, offer improved flow from one valve to the next via their positioning in a more directly opposite manner, with further gains had by the room which this setup allows for larger valves.