“The Chrysler Hemi” by Andy Tallone

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“The Chrysler Hemi”

When Japan bombed Pearl Harbor on December 6, 1941 it touched off World War II and mobilized the entire country behind the war effort. This included the auto industry. Ford, Chrysler and GM stopped building cars in 1942 and started producing tanks, planes, amphibious landing vehicles, machine guns and boatloads of other stuff, all to help win the war. Chrysler was, among other things, building aircraft engines and late in the war had been tasked to create an inverted V12. They determined that it would be a ‘hemi’. While the project stalled when the war ended, all that research and development work by Chrysler engineers was still there, waiting to be applied.

First off, what’s a ‘Hemi’? It’s shorthand for an engine with ‘hemispherical combustion chambers’. In other words, the right-sized ball would drop half-way into a hemispherical combustion chamber. It placed the intake and exhaust valves at angles facing one another, which opened the flow paths up to increase flow, and allowed more centrally-located spark plugs for better and faster fuel burning. At the time, this was state of the art engine design, widely used on OHV motorcycle engines of the era. It’s a more complex engine and more expensive to manufacture because the valves aren’t all neatly lined up like in most 6-cylinders of the day.

So, when the war ended and civilian car production resumed in 1946, Chrysler’s brain trust was noodling about the hemi. Their current engine line was aging and desperately in need of replacement. Their flathead straight-6 and straight-8 had been in service since the 1920s. What’s more, word was spreading that GM was getting dangerously close to introducing a new line of lightweight, high-compression OHV (Overhead Valve) V8s. So, those same engineers put all that hard-won knowledge and experience to work designing a new line of engines of their own.

Chrysler’s Engine Development Chief Ernie Code and Tom Hoover (who later gained notoriety in Hemi drag racing) designed an engine that prioritized airflow over packaging. The new engine had two rocker arm shafts per cylinder bank, supporting the intake and exhaust valves which were at a 27.5-degree angle to one another. It made for a wide cylinder head and big block, and with the casting techniques in those days, that made it a heavy engine, around 700 pounds. A typical 1950s Chevy small block weighed around 550 pounds. That’s a big difference.

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Cadillac and Oldsmobile launched their futuristic new OHV V8s in 1949 as the world watched. Chrysler introduced it’s first OHV V8, the 331 ci (cubic inch) Chrysler FirePower Hemi in its full-size car line in 1951 through 1955. In 1952 they downsized it to 276 ci for Desoto duty under the name Desoto Fire Power, and in 1953 they downsized it again to just 241 ci as the Dodge Red Ram Hemi. They punched it out again on 1956 to 315 ci and again in 1957 to 325 ci still under the Red Ram banner and only used in Dodges. In 1956 they arrived at 354 ci with the new Chrysler FirePower Hemi and in 1957 one last enlargement took it to 392 ci. This last entry is the most famous of all, used for decades in drag racing. Bulletproof, they took well to boosting and were capable of making big power.

But alas, the high cost and complexity of manufacture, and the advancement of other, simpler designs spelled the end of Gen I (1st generation) Hemi production, replaced by Chyrsler’s new B-block Big Blocks and Wedge motors. Simpler and cheaper to produce, and lighter, they could make almost the same power if done right.

The sunset in Hemi land from 1958 until the mid-1960s. By this time the muscle car power struggle was on and running at full throttle. The Big 3 were each trying to outdo the others in this horsepower arms race. Chevy had launched its game-changing small block V8, now up to 327 ci. They also had their W-series big block in 348 and 409 ci. And soon they would launch their Gen IV big block 396. Ford came out with their FE big block engine family in 1958 and now it was up to 390 ci and growing. Chrysler had its own big block family, two actually, the B- and RB-series big blocks. B stood for “Big” and “RB” stood for “Raised Block”, which had a taller deck height to support the longer stroke of the 440.

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Chrysler started with the big RB block and built a new set of hemi heads for it that were massive. And heavy. They had huge intake and exhaust ports and gigantic valves (2.25” intakes and 1.94” exhausts set 30-degrees apart this time), and a wild valve train that again used two rocker arm shafts per bank with long and short push rods that took divergent paths. When introduced in the 1966 model year, the 2nd gen 426 Hemi made an advertised 425 hp and 490 lb-ft of torque. Both numbers were grossly understated. Chrysler was concerned with rising insurance costs and didn’t want to scare the underwriters.

The 426 Hemi was and is one of the most legendary engines of all time. It’s big, it’s mean, it’s brutishly handsome and it makes power and torque like nobody’s business. Like their predecessors these were bulletproof engines that loved to be supercharged. Gen II Hemis fueled some of the world’s most famous and successful drag racers and have made as much as 4,500 hp, blown on alcohol. That’s how solid the 426 Hemi was and how good it was at flowing air.

The 426 Hemi stormed through the 60s as the top dog, the biggest, baddest dude on the block. The Chevy 409 and the later 427 hit that number, but it was probably more honest than the Hemi’s. Most people think that 425 hp-claim was a joke! Modern day dyno pulls have confirmed they were in the 530 hp-range. Only the 1970 Chevy LS6 454 beat it. Hemis were insanely expensive engines in their day. At around $900 the option package represented a 31% increase in the price of the car, at a time when a ’69 Road Runner MSRP’d for $2,869.

But the Gen II Hemi was not only expensive and massively heavy on the front end, but they were hard to live with in the real world. Great for racing, those two big carburetors swallowed gas and didn’t like low speeds or stop-and-go traffic. They loaded up, fouled plugs, ate tires and made too much heat. Those factors along with the astronomical insurance premiums, which could be as high as your car payment on a Hemi, doomed it to tiny sales numbers. Despite appearing in Dodge Coronets, Super Bees, Chargers and Challengers and Plymouth Belvederes, Road Runners, GTXs and ‘Cudas, over 6 model years (1966-1971) of production only 10,669 were built. The Malaise Era with its oppressive smog, safety and fuel mileage regulations killed performance starting in 1971, which also happened to be the last year for the 426 Hemi.

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The lights went out on the Chrysler Hemi for 32 years. Then a newly revived Chrysler came at it again with a Gen III Hemi in 2003 to replace the ancient 5.9-liter LA small block V8. The new 5.7 Hemi V8 made its first appearance in the 2003 Dodge Ram 1500 and once Chrysler got back in the business of rear-wheel drive cars, its use expanded into its full-size line, Chrysler 300, Dodge Charger, Magnum and Challenger.

Over the next two decades the evergreen Hemi would expand to 6.1, 6.2 and 6.4 liters, it would be supercharged, and it would break the bounds of peoples’ thinking of what a street engine could be. Starting in 2015 Dodge used clever supercharging and inter cooling to create a 707 hp monster in the Hellcat. Further variants with names like Demon and Redeye made crazy horsepower all the way up to 1,025! In a street car! With financing!! And a factory warranty!!! Holy crap!!!! You could kill yourself with that much horsepower.

A 2023 Dodge Challenger SRT Demon 170 can do the quarter-mile in 10.8 seconds at 131 mph from the factory! They come with a crate in the trunk with a bunch of drag racing goodies that they couldn’t put on it as a street car and sell it to you. But no one said the owner couldn’t put the goodies on himself, after the sale.

This new engine was designed from a clean sheet of paper with no physical connection to either previous generation of Hemi, with the exception of calling the 6.4-liter a 392 to honor the biggest engine in the 1st-Gen Hemi family. The cam was set high in the block to both shorten the push rods and to allow more room for expansion via a longer stroke. The combustion chambers are true hemis (half a sphere) with huge valves set at 34.5 degrees from each other and two spark plugs. The deep skirt block was cast in iron with aluminum heads. The intake and exhaust ports were large and flowed well. It had the same 4.4” bore center as the small block Chevy. It was built to be strong and to make big power when supercharged.

Because of the Gen III Hemi, the Dodge Challenger was able to not just compete in the big horsepower game, but lead it. The Hellcat was the first mass-produced car to cap 700 hp and it didn’t end there. When it happened in 2015, no one else had anything close. By the time they’d rallied their resources to respond, Dodge had already blown past than number and was now about 800, then soon 1,000.

The Hemi was a legend in its 1st-generation in the 1950s, and the Gen II was certainly legendary in the 1960s. And this new Gen III Hemi carries on that tradition brilliantly, exceeding it even, by a wide margin. They called the small block Chevy the ‘Mouse Motor’, so naturally the Chevy big block was a Rat Motor. In the same vain, the Chrysler Hemi was the ‘Elephant Motor’.