Few rivalries in American automotive history are as storied and intense as that between Ford's Boss 429 and Chrysler's 426 Hemi engines. The big-block powerhouses epitomize the pinnacle of displacement-heavy engineering during the muscle car era when Detroit's Big Three were locked in a high-stakes battle for supremacy on both the street and the racetrack.
In the late 1960s, the Boss 429 was born out of the necessity of hom*ologation for Ford to compete against the dominant Mopar. Yet, both would win the hearts of muscle car lovers by bringing unparalleled performance to race-specific and production cars.
To ensure accuracy, HotCars has sourced facts, stats and specs from the following sources for this article; Classic.com, Hemmings, and Ultimate Muscle Car.
Ford
Ford is one of the most recognizable vehicle brands on the planet, and has revolutionized the industry with some incredible cars over the years, including the Mustang, GT40, Maverick, and a lot more.
- Founded
- 1903
- Founder
- Henry Ford
- Headquarters
- Dearborn, Michigan
- Current CEO
The Boss 429 And The 426 Hemi Were Fierce Race-Bred Competitors
The 426 Hemi: A Legend Is Born
In 1963, Chrysler chairman Lynn Townsend set his sights on becoming a driving force in America's newest racing series by winning the inaugural running of its biggest trial: the 1964 Daytona 500. Engineers had just ten months to design and build the new engine from scratch before the February 23 start. Fortunately, Chrysler had been working on hemispherical combustion chamber technology since WWII.
But it was a much different animal than the previous Max Wedge engines. The hemispherical cylinder head design allowed for bigger intake and exhaust valves, meaning more fuel and airflow - essential for high performance. Placed in a Plymouth Belvedere, the first incarnation of the 425-horsepower 426 Hemi stamped its authority on the world of speed, taking the top four spots in the 1964 Daytona 500.
Subsequently, the Hemi's first victory led NASCAR to implement hom*ologation rules, meaning that racing engines had to be available for production cars, which Chrysler accomplished in 1966 with a road-appropriate model.
The Ford Boss 429 V8, A NASCAR Contender
Ford was known for producing successful high-performance, big-block engines, such as the 427 cubic-inch and 428 cubic-inch powerplants. But the engineers were working with older racing technology and sought to develop one based on its newest 385-series engines - specifically to challenge the extremely powerful but aging Chrysler 426 Hemi in NASCAR's Grand National Division.
The company introduced the Boss 429 in 1969, featured in the Ford Galaxie for NASCAR purposes. However, for the hom*ologation requirements, the Detroit giant looked beyond its bigger-bodied cars like Torino and the Fairlane and decided to drop it into one of America's favorites: the Mustang.
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How The Boss 429 And The 426 Hemi Stack Up On Paper
Boss 429 and 426 Hemi Specs
Engine | Boss 429 | 426 Hemi |
Displacement | 7.0 Liters | 7.0 Liters |
Bore | 4.36 Inches | 4.25 Inches |
Stroke | 3.59 Inches | 3.75 Inches |
Horsepower | 375 HP @ 5,200 RPM | 425 HP @ 5,000 RPM |
Torque | 450 LB-FT @ 3,400 RPM | 490 LB-FT @4,000 RPM |
(Specs courtesy of Hemmings)
The Hemi's Evolution And Design
The basis of the Hemi design is fairly simple. In fact, the first was an inverted V16 version that was supercharged and turbocharged, then stuffed into a P-47 Thunderbolt as an experimental design for the U.S. Army Air Forces. Since its 2,500-horsepower didn't hit the skies until July 1945, it never saw production, but it gave Chrysler engineers a beginning point for their first automobile engines.
The shape of the cylinder head's combustion chamber on the iron-block 426 Hemi, like others, is roughly half of a sphere - for instance, a melon cut down the middle and scooped out. Since the spark plug can be placed at top-dead-center, it shortens the burn distance of the air and fuel mixture. Due to the hemispherical shape, flat-top pistons could not produce sufficient compression, so domed pistons were used to make up the difference.
The 426 Hemi was often paired with the A833 4-speed manual transmission or the drag strip-ready TorqueFlite automatic. Hemi cars equipped with automatics featured a 3.23:1 gear ratio and an 8.75-inch rear end, with Sure Grip available as an option for traction. Meanwhile, the manual models came standard with a 3.54:1 gear ratio and a 9.75-inch Dana 60 rear end, which required Sure Grip. Nevertheless, dealerships around the country offered further customization.
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The Boss' Emergence
The Boss 429, on the other hand, was an evolution of Ford's planned lineup with the 385-series - also called the Lima engine family - which included popular overhead valve, iron-block V8s like the 302, 351, and 460. Interestingly enough, the Boss 429's cylinder heads were semi-hemispherical, featuring a crescent-shaped combustion chamber design. This improved airflow and combustion efficiency, similar to the Hemi 426 but with Ford's unique twist.
The only transmission option available was a Toploader four-speed, paired with a 9-inch rear end that featured a standard 3.91:1 ratio with Traction Lok. Additionally, buyers could opt for a 4.30:1 Detroit Locker for further road-gripping traction. But all of this power and performance came at a cost, as the Boss 429 was nearly $5,000 in 1970—roughly twice the price of the base model V6 Mustang.
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These Hemis Are The Most Powerful Of All Time
When the LEAST powerful engine in a lineup of HEMIs makes 425 horsepower, you can bet it's an exciting rundown of American performance. You'll never guess how much power the MOST potent HEMI on this list makes though as it's a BIT crazy.
The Boss 429 Was A Standalone Model, But Many Models Boasted The 426 Hemi
Chrysler's Flagship Powerplant
When the 426 Hemi debuted in 1966, it was one of the most sought after optional extras. But since power always comes at a price, getting the desirable engine required sacrifice. At a time when a base model Dodge Charger was $3,100, it was an extra $800-$900 (depending on dealer location) to fill out the engine bay with the Hemi's girth. Nevertheless, the company offered the power package in no less than 14 different street-legal variations.
Notable 426 Hemi Applications
- Dodge Charger (1966-1970)
- Plymouth Barracuda (1966-1971)
- Chrysler 300 (1966-1971)
Chrysler put 10,669 426 Hemis into their cars during an eight-year production run. While fitting the 7.0-liter engine was a breeze for Mopars, the same couldn't be said for the Blue Oval barnstormer.
Fitting A Muscle Car Engine In A Pony Car
Ford chose the Mustang as the basis for the Boss 429, despite the fact that installing the engine in the rear-wheel-drive Torino - a car similar in size to the Charger - would have been easier. The Mustang was Ford's most popular sports car at the time, so they wanted to give the new engine plenty of exposure. However, shoehorning the Boss 429 engine into the Mustang required major modifications.
Mustangs came off the line at Ford's Rouge plant in Dearborn, Michigan, and were then driven to Kar Kraft in nearby Brighton, where they underwent extensive alterations. The front suspension and shock towers were moved to the sides, the battery moved to the trunk, and a rear sway bar was added, so the car could handle the engine's weight. Unfortunately, all of this meant no room for an air conditioning unit.
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A Short-Lived Rivalry Between Chrysler And Ford's Big Blocks
The Short Life Of Ford's Boss 429
The 1960s and early 1970s saw intense competition among American automakers, culminating in the muscle car wars. The 426 Hemi and Boss 429 were central to this rivalry, with each pushing the boundaries of performance and innovation, but both were relatively short-lived. Just one year after its debut, sales started to drop off for Boss 429 Mustangs and with higher production costs at Ford, that year would be the last.
Unfortunately, new Ford President Lee Iacocca's idea to stuff the Boss 429 engine into a winged, elongated version of the Torino - called the King Cobra - was dropped after only two prototypes were built. However, as the Boss 429 engine was hom*ologated in the Mustang, Ford used it in NASCAR until 1974 with other platforms.
The 426 Hemi Gets Its Wings Clipped
In 1971, Chrysler's 426 Hemi was under the watchful eye of NASCAR officials. After the engine was placed in new "aero cars" like the Dodge Charger Daytona and the Plymouth Superbird, NASCAR put rules in place to restrict engine size to five liters in combination with more aerodynamic cars.
Therefore, the benefits of the engine on the track were lost. After tightening federal emissions regulations and increasing insurance costs, high-performance engines were less cost-effective and feasible for mass production.
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Legacy Of The Boss 429 And 426 Hemi Engines
There has been wide speculation for over a half-century that both the 426 Hemi and the Boss 429 had more power than what was advertised by the automakers. In two words, that's right. Chrysler and Ford - much like other muscle car manufacturers - deliberately downplayed horsepower figures so buyers wouldn't be stuck with high insurance premiums.
Many estimate that the Boss 429 was capable of anywhere from 420 to 500 horsepower depending upon how high the rev limiter is raised. On the other hand, the 426 Hemi was good for at least 470 horsepower, with some claiming figures nearing 600 horsepower in race-spec versions. Ford only cranked out 1,359 Boss 429s over two years of production, making it one of the rarest Mustang variations.
These Legendary Detroit Engines Fetch Big Bucks Today
As can be expected, they fetch fees at auctions that are well into the six-figure range. In 2023, a 1969 Boss 429 was sold at Barrett-Jackson Scottsdale for $374,000. Nevertheless, the median price runs just north of $62,500, which should give hopes for enthusiasts looking to snatch up a car nearly destined to go up in value.
Some may believe that, since over 10,000 engines were produced and put into over a dozen different models, that the 426 Hemi would be a bargain, but that will depend heavily on the model desired. Enthusiasts can generally obtain a Plymouth GTX or a Dodge Coronet with a 426 Hemi under the hood for the price of a new mid-size passenger car.
However, some of the highest auction items ever recorded in the automotive world have been associated with the engine. For instance, at Mecum Auctions in 2014, a Hemi-powered 1971 Plymouth Barracuda convertible sold for over $3.5 million.
Sources: Classic.com, Hemmings, Ultimate Muscle Car
