World's Rarest 1969 Plymouth HEMI Cuda Hides a Forgotten Prototype Under the Hood

The list includes the Plymouth Superbird and Dodge Charger Daytona twins, as well as the Charger and the GTX. And, of course, I can't forget the Plymouth Cuda convertible, which spawned only 14 examples in 1970 and just seven in 1971. There's also the 1968 Barracuda B029, a factory-made Super Stock dragster fitted with the 426 HEMI. Plymouth built only 50 units, and not all survived until 2023.

But none of the cars above are as rare as the blue, HEMI-badged 1969 Barracuda you see here. Wait, what? Plymouth offered the mighty 426 in the 1969 Barracuda too. Nope, it did not. This Barracuda joined HEMI ranks thanks to an engine swap. But here's the catch: the HEMI under the hood is not a 426 but a forgotten prototype Chrysler built in the 1960s.

I'm talking about a big-block mill called the ball-stud HEMI. Design in the late 1960s, it was supposed to enter mass production in the early 1970s and replace the low-volume 426 HEMI and the 383- and 440-cubic-inch (6.3- and 7.2-liter) powerplants. Internally known as A279, the engine got its name from the valvetrain configuration, which used ball-stud rockers.

Based on a low-deck block, the lump was planned to become available in 400- and 440-cubic-inch sizes, but Chrysler also considered a 444-cubic-inch (7.3-liter) version. The engine was also scheduled to get cast aluminum pistons, intake and exhaust valves the same size as the 426 HEMI, and a compression ratio of around 10:1.

Although it was supposed to replace Chrysler's most powerful engines, the ball-stud HEMI was restricted to a four-barrel carburetor setup due to stricter emissions standards introduced in the US at the time. Testing showed that the ball-stud mill outperformed the four-barrel 440 but lagged behind the 426 HEMI.

Unfortunately, the project was laid to rest in late 1969 due to financial issues, upcoming emissions, and fuel efficiency standards. Chrysler reportedly built anywhere from three to 12 prototypes, and all were scrapped except for the one in this Barracuda. How did it manage to escape? Well, that's a bit of a mystery, but we know it spent many years in storage before it ended up with the guy that married it to the 1969 Cuda.

Featured by YouTube's "Hot Rod Hoarder," the Mopar is also a historically significant rig. It left the factory with a 440-cubic-inch V8 engine, which makes it one of only 340 units produced, and it was turned into a Super Stock racer by iconic drag racing outfit Sox & Martin. The car has since been restored to factory specifications, save for the addition of the ball-stud V8.

The engine itself is no longer stock either. Bored .30 over and fitted with many upgrades, including a new crankshaft and intake manifold, the HEMI now displaces 481 cubic inches (7.9 liters) and generates more than 400 horsepower. No longer with the owner who modified and installed the engine, the Barracuda now lives in the National Auto and Truck Museum in Auburn, Indiana.

Granted, the fact that the engine is no longer 100% authentic is a bit disappointing, but at least it survived to tell its story. It's also decidedly pretty and runs in a nicely preserved classic.