Unleashing Power: The Mopar 426 Hemi Engine Explored

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The Mopar 426 Hemi was the beast of the muscle car era, but its use for the street might only have happened due to a NASCAR feud first.

Chrysler produced the 7.0L (426 ci) Hemi engine from 1964 - 1971. Nicknamed “the elephant,” the engine produced 425 hp and 490 lb-ft of torque. Even though the first two years were only used in racing, from ‘66 on, the 426 Hemi made its way into various Dodge and Plymouth muscle cars.

If you are a classic car nut like us, you know that the holy grail of muscle car motors is the 426 Hemi engine. Its presence on the racetrack thrilled fans to no end, but its actual claim to fame was on the street, where young people raced the beast and collected pink slips. (There isn’t a baby boomer alive who didn’t marvel at the growl of the raised block V8 when it pulled up to the Tasty Freeze). So, when a ‘71 Hemi ‘Cuda convertible sold in 2007 for $2.2 million, and then another sold in ‘14 for $3.5 million, and as recently as 2021, one didn’t sell despite a $4.8 million bid, we realized that we aren’t the only ones who loved the Mopar 426. What makes this motor so unique? Let’s look at the Mopar 426 Hemi to discover why people are spending lots of money for the pleasure of driving one.

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The Roots Of The Hemi Engine

While the 426 Hemi gets all the glory, it wasn’t the first hemispherical engine that Chrysler created. During the close of WW II, Chrysler developed an inverted Hemi V16 engine for the P-47 Thunderbolt aircraft. The XIV-2220 was never put into production (due to the war ending), but Chrysler took the lessons it had learned and, over the next few years, adapted the concept of the Hemi to their line of full-sized automobiles.

When it debuted in 1951, the new “Firepower” engine, the 331 ci engine produced 180 hp, began to appear in Chrysler vehicles. Before long, every division (except Plymouth) produced their variant of the Hemi engine. The hemispherical engine continued in various displacements until 1958 when Mopar abandoned the Hemi to work on its family of B-block Wedge engines.

But in the early sixties, Mopar needed an engine to outrun the Ford 427, which was being added to the racing scene in 1963. Having had success with the Hemi before, Chrysler turned to the tried and trusted motor, but this time they gave the engine some serious attitude. The Hemi was dubbed the “elephant” because of its size, weight, and power. The engine was built on 10.72 deck height with more than adequate bore spacing (4.04) (which would allow it to be stroked for higher displacements that race cars needed).

The design of these Chrysler engines relied on hemispherical combustion chambers with modified cylinder heads that could create a more dynamic force for power outputs. Mopar increased the size of both the intake and exhaust valves (2.02 and 1.94) and equipped a cross-ram manifold to provide additional airflow into each combustion chamber. Other racing components were added, like a front sump oil pan to keep the engine from overheating, and larger steel long tube headers made the exhaust blow out of the back with an aggressive growl.

The Hemi Goes Racing

The rise in popularity of stock car racing spurred Chrysler to resurrect the Hemi engine for use in Nascar in 1964. In the inaugural Daytona 500, Richard Petty won by driving a Plymouth Belvedere equipped with a race Hemi. (Cars with the 426 Hemi placed first, second, third, and fifth). The engine's success forced Nascar to ban new engines due to a lack of homologation requirements. (Ford and Chevy were clamoring against the new motor, which may have influenced the decision-makers). Chrysler spent the next year trying to figure out how to offer a street version of the Hemi for general production. (The result was a “Street Hemi” with lower compression that appeared in Dodge and Plymouth cars for the ‘66 model year).

When Mopar charged back into racing for the 1966 season, the 426 returned with a vengeance. Richard Petty won the Daytona 500 again, and David Pearson won the season title in a Mopar customized Dodge Charger. (Pearson won 15 races with 26 top-five and 33 top-ten finishes). The wins elevated the presence of the 426 Hemi and put the racing world on notice as the engine to beat.

The success of the 426 Hemi would continue into the 70s when Buddy Baker set the racing world on fire with a more than 200 mph run in a Dodge Charger Daytona. The King, Richar Petty, driving the No. 43 Plymouth, would dominate the circuit. Richard Petty would win the Daytona 500 again in 1971, and repetitive wins in 73-74.

The Hemi also made its way onto drag racing in NHRA and AHRA. The engine’s design made it easy to bore the cylinders, reaching displacements off the charts.

The “Hemi” Comes To Main Street

When Mopar unleashed the Hemi for the general public in 1966, the production motor was much more tame than the racing version. With a reduced compression ratio of 10.25:1 (vs. 13.5:1 for the race car), a lower-lift camshaft, and a 2 x 4 bbl carburetor, the Hemi made its debut as an option for the Dodge Charger/Coronet and the Plymouth Belvedere/Satellite models. The Hemi produced 425 hp and 490 lb-ft of torque. The sales brochures touted the V8 engine as part of the new “rebellion” and encouraged young buyers to “take it home and stir things up.”

Even though the motor was not as powerful as the racing version, it was still quick. The Hemi was capable of 5.8 seconds in the 0 - 60 mph stretch, which made them faster than most everything on the road. There was a definite growl to the engine that could intimidate the best Ford Mustang owner and make them quake in their boots when the Hemi pulled up alongside.

Both Dodge and Plymouth charged extra for the Hemi engines, which prevented many young owners from purchasing the Hemi beast. The added expense often raised the price of the vehicle to nearly $4,000 (which was a lot of money in those days). In addition, the new V8 required owners to use premium with they went to pump gas, which only added to the expense.

In just a few years, the Hemi was offered as a part of iconic muscle cars like the Dodge Challenger, ‘Cuda, Road Runner, and Superbee. While 1970 would be Hemi’s best production year, the cars were made in such limited numbers that today, they are among the rarest classic cars and fetch top dollar at auction.

The Hemi Gets Kicked To The Curb

Hemi production continued until 1971 when it became clear that the muscle car era was closing. When the government announced impending emissions regulations would soon be enacted, Chrysler abandoned the Hemi. The engine was expensive to build, and with such a lack of demand, Mopar thought it best to abandon it. In 1972, automakers detuned their other engines with lower compressions and power ratings. (A habit they would continue during the ‘70s and early ‘80s, in what classic car lovers often call the “malaise era”).

The Hemi Today

Due to the scarcity of engines, any classic car with a 426 Hemi is a valuable commodity. (For example, a ‘71 Hemi ‘Cuda with manual transmission failed to sell in 2021, despite having a 4.8 million dollar bid. Another sold in 2014 for $3.5 million). While there is a strong Hemi community, the Hemi 426 is considered among the rarest collectible cars on the planet.

If you are planning on trying to find a 426 Hemi for your classic car rebuild, good luck trying to find one. You should plan on spending close to $30k for a Hemi crate engine for a 426. (We found one on Ebay for $28k).

The Specs of the Hemi Engine

The following is a listing of the specifications of the 426 Hemi engine.

7.0L 426 V8 Hemi Engine Specification
Production 1964 - 71 (Racing)
1966 - 71 (Production models)
Configuration Naturally aspirings
Displacement 426 cubic inches
Horsepower 425 hp
Torque 350 lb-ft
Bore 4.25 inches
Stroke 3.75 inches
Compression Ratio 12.5:1 (racing)
10.25:1 (street production models)
Firing Order 1-8-4-3-6-5-7-2
Block Cast Iron
Heads Iron
Intake manifold Dual plane aluminum
Exhaust manifold Cast Iron
Intake and Exhaust Valves 2.25 (intake) - 1.94 (exhaust)
Deck Height 10.72 inches