The match that lit the “horsepower wars” on fire in the early 1950s through to the oil crisis of the 1970s was struck by the Chrysler Corporation, almost by accident. The company had developed a WWII fighter plane engine which had been rigorously tested and proven. However, the engine never went into production and was scrapped. That “failure” would lead to one of the most iconic engines in all of hot-rodding — the Hemi.
Chrysler engineers adapted the concepts they used for their wartime engine in the FirePower line of V8s powering the 1951 Chryslers. These were the first “Hemi” engines for mass production in America. By the ’60s, Chrysler had popularized (and trademarked) the term “Hemi,” which was shorthand stemming from the hemispherical combustion chamber design.
A cylinder head with a hemispherical combustion chamber has excellent airflow due to its design. While there have been several attempts at multi-valve configurations, the hemispherical chamber as we’re discussing here has only two large valves per cylinder. The intake and exhaust valves sit on opposite sides of the chamber, creating a “crossflow” head design.
Hemi Is More Than Just A Name
Most muscle car enthusiasts today associate anything hemispherical (not just the trademarked “Hemi”) with Mopar. But Chrysler wasn’t the only auto manufacturer to use a hemispherical cylinder head. In the early part of the 20th century, many automakers toyed with hemispherical designs, including Alfa Romeo, Aston Martin, Porsche, Jaguar, Ford, Toyota, and others. Chrysler, however, perfected the Hemi and used it to boost sales.
Aside from the WWll big Hemi fighter plane engine, nearly all folks consider the early ’50s 331 Chrysler FirePower to kick off the true OEM Hemi engines. — Mike Lozano, Egge Machine
The original FirePower Hemi engine is sometimes referred to as the Type-1. The Chrysler Corp. followed that up with DeSoto’s FireDome and Dodge’s Red Ram, referred to as Type-2 and -3. These early Hemis have different displacements and deck heights and are collectively known as Gen-Is. With this naming convention, Gen-II would be Type-4, and the Gen-III 5.7-liter is Type-5, and so on. Clear as mud?
The 331-ci Chrysler Hemi V8 weighed nearly 1,000 pounds and produced 180 horsepower at 4,000 rpm, which was impressive for its time. It came with a forged-steel crank and large valves (1.81-inch intake and 1.50-inch exhaust), giving it superb flow.
The hefty 331 had a cast-in-the-block bellhousing flange that added weight, but it was later dropped. Early hot rodders caught on to the Hemi’s airflow advantages, and soon Chrysler was bumping the displacement to 354 ci, producing 350 horsepower, and then 392 ci, with an incredible 390 horsepower. This engine was used for years in drag racing and hot rodding.
After the small-block Chevy was introduced in 1955, Chrysler’s Hemi engines started to fall out of favor with the hot rod crowd. That is, until the 1960s. That’s when Chrysler rolled out a powerful new racing engine designed to crush the competition on the high banks of Daytona.
The 426 “Race Hemi” was dominant, so much so that NASCAR banned it a year later and told Chrysler it had to make a street version to compete. Instead, Chrysler spent the 1965 season drag racing with the 426, soon becoming the go-to engine for drag racers. The 426 Gen-II “Street Hemi” was sold to the public to appease NASCAR’s requirement that engines must be homologated to race.
According to Egge Machine‘s Mike Lozano, “Production cost was the temporary inhibitor of the Gen-I Hemi engine, before the reinvention to the Gen-II 426 Elephant engine.”
Early Versus Late Hemi Engines
Since he is regarded as the resident Hemi historian at Egge, we decided to sit down with Lozano for a little direct question and answer session about the differences between early and late Hemi engines.
EngineLabs: What were some of the differences between early Hemis and current iterations?
Mike Lozano: “There are several differences between all of the Gen-I Hemis to the current Gen-III Hemis. Examples include aluminum cylinder heads and composite materials [in the modern versions] versus the use of nearly all cast-iron in the early engines. All Gen-I engines had a true hemispherical chamber versus the quench chamber seen in the Gen-III. Then there is the use of a single spark plug in the originals compared to the twin spark plugs in the Gen-III design. Obviously, the induction system is completely different between the carbureted original and modern factory EFI. The original was a flat-tappet engine and the modern version uses hydraulic roller lifters, and the list goes on and on…”
Many people think of the 426 as the best Hemi. What is your take?
ML: “As far as “Best Hemi,” the Gen-III takes it with the best overall performance and efficiency, but the Gen-I engines take the ‘cool factor’ title! The 426 has cemented its place in history with its massive brute power and nitro drag racing roots.”
Were any of the other Chrysler division Hemi engines better than the FirePower?
ML: “The Chrysler FirePower engines seemed to have taken the lead compared to its cousins in the horsepower race, and thus racers and the aftermarket caught onto this as well.”
Were there any other iterations of the Gen-II Hemi besides the 426?
ML: “The Gen-II engine only came in 426 ci, but there was the ‘Street Hemi’ and the ‘Race Hemi’ with various power-enhancing parts toward the Race Hemi, such as high compression (12.5:1) race pistons, bigger camshaft, and cross ram induction. In early development (1964) for NASCAR, Chrysler decided to build a special DOHC version with the code ‘A925’. Although development issues — and NASCAR almost immediately banning exotic engines — killed the program.
It is worth noting that nothing is interchangeable with earlier Gen-I Hemi engines and the Gen-II (or even Gen-III) variants, but they are all related.
10 Interesting Facts About Hemi Engines (In No Particular Order)
- The Gen-II 426 Hemi engine dominated the Daytona 500 on its debut in 1964, taking the top three spots. Richard Petty won by more than a lap in his Plymouth Belvedere. NASCAR changed the rules for 1965, forcing Chrysler to develop a street version of the 426 Hemi before it would be permitted to compete again.
- The 426 Hemi was originally designed as a pure racing engine, and the same basic design continues to power NHRA cars today in Top Fuel, Funny Car, and other classes.
- The XI-2220 was an experimental 2,500-horsepower, 2,220 ci (36.4-liter) liquid-cooled inverted-V16 aircraft engine designed by Chrysler in 1940. By the time it was ready for use in 1945, the war was already over. But the technology was the basis for Chrysler’s first automotive Hemi engine designs.
- The original hemispherical combustion chamber engine design was called FirePower and was used in 1951 model-year Chrysler vehicles. It produced 180 horsepower. Dodge, DeSoto, and Imperial had their own variants of the Hemi engine.
- 11,000 Gen-II 426 Hemi engines were produced for customers, which made the engine sought after by collectors, racers, and hot-rodders alike.
- The Gen-II 426 street Hemi made an average of 350 horsepower in 1971, while the Gen-III 5.7-liter Hemi produced 345 horsepower when it debuted in 2003.
- In 1964, “Big Daddy” Don Garlits broke the 200-mph barrier with a Gen-II 426 race Hemi-powered car, running the quarter-mile in 7.78 seconds at 201.34 mph.
- DeSoto introduced its version of the Hemi, called “FireDome” in 1952, with a displacement of 276 cubic inches (4.5 liters) rated at 160 horsepower. The company sold 50,000 vehicles with the engine until it was replaced in 1954.
- The bore-spacing of Chrysler FirePower engines was 4.5625 inches, the largest of all the Gen-I Hemi engines. Most used a two-barrel carburetor, except the 1955 Chrysler C-300, equipped with dual Carter WCFB four-barrel carburetors and rated at 300 horsepower.
- Gen-II 426 engines were the first to be officially called Hemis, and Chrysler trademarked the name. The 426 Hemi was nicknamed the “elephant engine” due to its high horsepower, heavy weight, and large physical dimensions. With a deck height of 10.720 inches and 4.800-inch bore spacing, it was the biggest engine in racing at the time.