Chrysler Hemi | Legendary engines

The Chrysler Hemi engine is as profoundly etched in the American Automotive psyche as the Ford Flathead and Chevrolet LS small block. 

The Hemi is so called because of its half-hemispherical combustion chambers and rounded pistons, which have a smaller surface area than a flat head piston, allowing less energy to escape from the engine in the form of heat, the peak pressure is higher, and you get more power. Hemi-engine valves can also be bigger, allowing more air into the engine and the quicker release of exhaust gases, with spark plugs placed in a more efficient position – top dead centre of the cylinder, which shortens the burn distance of the air-fuel mixture.  

While the Hemi engine is as American as Budweiser and burgers, the USA wasn’t the first country to build a hemispherical engine, and who exactly did is up for debate; it’s thought the half-sphere combustion chamber originates as far back as 1901 – not long after the combustion engine itself. Belgian company Pipe is believed to have been the first to manufacture a hemispherical engine for sale in 1905. Two years later, Fiat used the technology for Grand Prix racing under the bonnet of the 130 HP.

Chrysler’s first Hemis weren’t used in cars at all but instead for the military, in the M47 Patton tank and the P-47 Republic Thunderbolt fighter aircraft, before the technology trickled down into civilian life in 1951 in the first-generation 331ci (5.4-litre) 182PS (134kW) Firepower overhead-valve V8. By 1958, the technology had spread across all of Chrysler’s brands, including Imperial, Desota (where it was called the Fire Dome) and Dodge (Red Ram) in capacities ranging from 4.0 to 6.4-litre. 

The second-generation hemispherical engine, the 426, was launched in 1964 and was the first motor to carry the legendary Hemi nametag. Legend has it that the CEO of Chrysler, Lynn Townsend’s son, came back from a day watching motorsport raving about the power of Pontiac race cars, which infuriated his father, who promptly demanded Chrysler build an engine that could win on circle-track and straight-line racing.

The result was the 6.9-litre V8 Hemi, built for the 1964 Plymouth Belvedere NASCAR, powering the car to first, second, and third place at that year’s Daytona 500. Dominating the podium was not a popular move with other teams, and the 426 was banned in 1965 because the engine gave an unfair power advantage and wasn’t available on a road car. 

A year later, the Hemi returned to NASCAR and made its first mass-market appearance in a road car when Dodge fitted a Street Hemi V8 to the Charger and Coronet. These road-ready motors had a lower compression ratio, milder cams, plus a toned-down intake and exhaust, but were still good for a healthy 431PS (317kW).

Around the same time, the Hemi earned its nickname – ‘the Elephant Engine,’ at the drag strip; it was massive and nearly indestructible, but also slower than the old 392. 

It wasn’t until 1966 when the 426’s full potential was unleashed, albeit accidently when Big Daddy Don Garlits, attempting to highlight the engine’s shortfalls, cranked the timing of his 426 dragster up to 40 degrees (the old 392 would crack its cylinder walls at 34 degrees) and went on to set a new world record crossing the finishing line at 214mph. 

Pushing the timing to 50 degrees freed up even more performance, with the car crossing the line at 219mph. As Garlits puts it, “That was it, that was the end of the 392 for me.” Dragsters running 426s have since produced more than 11,153PS (8,203kW) running the same cylinder heads and two-valve combustion chambers. 

While second-gen Hemi engines were reserved for race and high–performance road cars, the third-generation 5.7-litre Hemi was also fitted to mainstream machines like the Dodge Ram truck, Chrysler 300C saloon and Jeep Grand Cherokee offroader. The newer engine had near-perfect hemispheres and modern advances like fuel injection, variable valve timing, and cylinder deactivation.

A more potent third-gen version wasn’t introduced until 2005 – the 6.1-litre Hemi. A product of Chryslers’s Street and Racing Technology (SRT) division, the 6.1 brought power up from mid-to-late 300 horsepower to 431PS (317kW), thanks to a modified engine block, improved pistons, and a freer-flowing intake. Since then, the engine has spawned more and more powerful iterations like the 6.4-litre Apache and 6.2-litre Hellcat.

But the most powerful Hemi’s still carry the famous 426ci displacement of the Elephant Engine, and the most powerful of those is the Dodge Direct Connection 1500 Hemi crate engine, so named because it develops a cool 1,500 horsepower running on E85 ethanol.

The 1,500 is a fitting tribute to the Hemi engine, which can trace its roots back to WWII and has triumphed in NASCAR and NHRA drag racing alike. Could the dawn of the EV finally kill it? The burgeoning crate-engine market makes us think the Hemi might be harder to kill than even Big Daddy Don Garlits could ever imagine.