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.
Though used pretty extensively in early GP racing machines and high-end, small-scale production models, it wasn’t until Chrysler’s introduction of the 1951 “FirePower” engine that the use of hemispherical chambers really gained traction in mass-market cars. Another 13 years would pass, though, before the hemi became “the Hemi”, debuting in Plymouth’s ‘64 Belvedere NASCAR racer. Banned for race use in 1965 due to public unavailability, Mopar first offered the “Elephant” 426 in street cars for 1966. Now, just like Richard Petty’s dominate Belvedere, the Hemi once again owned the stock car circuit, easily powering David Pearson’s Dodge Charger to a championship win.
On the dragstrip, however, the Hemi was much less successful, with ET’s roughly half a second behind Chrysler’s older and supposedly technically inferior wedge head design—until Don Garlits, probably the best-known dragger of all-time, discovered the key to unlocking its potential completely on accident. Garlits, frustrated with the Thunderfist and its apparent underperformance, set out to speed its demise, and advanced ignition timing far past what he thought would be enough to blow it to shreds—but to Big Daddy’s surprise and delight, not only did the big-eared beast survive, it absolutely thrived on what he had planned to be its tortuous death, with more horses and lower elapsed times immediately available. Within a year, Hemi-powered top fuel dragsters were running low six second quarter miles, a whole one and a half seconds quicker than the old-wedge headers were capable of. To this day, aluminum engines based on the old 426 continue to dominate top fuel—the idea of these 21st century rocket sleds being propelled to 300 MPH, sub 5 second quarter miles half a century after its conception is shocking.
Original Hemi-equipped Mopars now command some seriously big dollars, and excluding Ford’s near-mythical 426 OHC “Cammer”, remain the undisputed kings of the Muscle era, powering some of the most insane road cars the world has ever seen. 426s typically dyno very near 500 bone-stock horsepower—now picture that kind of twist channeled through skinny, bias-ply tires, reined in by shoddy drum brakes, and approximately steered by over-boosted racks attached to a gigantic, thin-rimmed yacht mast. Oh yeah, during a time when 90 HP or so was considered completely adequate to power a rather large, base model family sedan. It was pure insanity; glamorous, dangerous, and within the reach of almost any 20-something with a good job—tragedy and triumph hand-in-hand through a thick cloud of acrid tire smoke and rich-running carbs, and it was the stuff legends are made of.