1970 Dodge Diamante: Mopar's Forgotten 426 HEMI-Powered Two-Seat Challenger

Inspired by an experimental aircraft engine, the first generation of Chrysler engines to feature hemispherical combustion chambers debuted in 1951 and powered the corporation's most potent production cars for the next seven years.

However, the idea was taken to another level during the early 1960s when an all-new 426-ci (7.0-liter) wad developed.

Initially a race engine meant to help the Mopar camp dominate NASCAR, the 426 HEMI was banned after its debut season since it wasn't used on a series-production model.

Chrysler didn't want to let the entire project go to waste, so in 1965 (for the 1966 model year), the so-called "street HEMI," a 425-hp road-legal production version of the engine, began appearing on the options list of several Dodge and Plymouth models.

Until 1971, when it was discontinued, the 426 HEMI became the most esteemed and sought-after American performance engine. Even more than half a century later, it's still an icon of the original muscle car era.

Apart from the legendary series production muscle cars it powered, the 426 HEMI was also used for several exciting Chrysler Corporation concepts, and in this article, we'll remember arguably the most exciting.

Developed to gauge interest in a two-seat, Corvette-rivaling Challenger

For the 1970 model year, the Chrysler Corporation unleashed a totally redesigned Plymouth Barracuda and a brand-new Dodge-badged sibling dubbed Challenger.

Apart from the exciting design, both models shared a common platform, the all-new E-body.

In the Dodge offices, management was searching for ways to promote its new model that, unlike the Barracuda, lacked a brand image.

One of the answers was the development of a unique show car that, apart from drawing the car-buying public's attention to the new model, also researched the interest in a potential HEMI-powered, two-seat E-body sports car that could go head-to-head with Chevy's hugely popular Corvette.

Dubbed "Yellow Jacket," the resulting show car started life as the very first convertible Challenger and the first E-body to receive the Elephant engine.

After it was assembled on the new Challenger line, the all-black car was sent to Synthetex, Inc. in Dearborn, where, among other upgrades, it received a custom Targa-style roof section with a retractable rear window, a bespoke power spoiler, side exhausts, and a stock Shaker hood.

From Yellow Jacket to Diamante

Painted in a unique shade of Pearl Yellow, the concept went on tour during the second part of 1969, but although it was met with a generally positive reaction, it wasn't the sensation that Dodge had hoped for.

While any plans for a two-seat E-body sports car were abandoned, the concept car itself was not.

Rather than sending it to the crusher or parking it inside a storage unit, management decided to transform it into a far more spectacular show car.

After it was sent back to Synthetex, the one-off Challenger received another round of comprehensive modifications.

While the Targa-style roof section was left untouched, the car's wheel wells were widened, the Shaker hood was swapped with a custom one, and the nose section was redesigned to resemble that of the Charger Daytona and Superbird "Aero Twins."

Christened Diamante (diamond, in Spanish), the restyled show car was painted in a special Pearl White Diamond coat rumored to be produced by crushing real diamonds and mixing them with the paint. But, as you can imagine, that rumor turned out to be false.

A far more successful show car

Retaining the 426 HEMI, albeit with a new, custom radiator that was required to clear the new, aggressively sloped hood, the Diamante made its debut at the 1971 Detroit Auto Show, which took part in the fall of 1970.

Unlike the initial Yellow Jacket, the redesigned show car, which was showcased on a stage that featured a million dollars worth of real diamonds, drew large crowds and received extensive coverage from the era's most famous automotive magazines.

After the Detroit Auto Show ended, the Diamante's impeccable pearl paint was badly damaged, and since the car was scheduled to take center stage at another event, it was sent to George Busti of Creative Customs for an urgent repaint.

The story has it that, in all the panic caused by the incident and the tight schedule, the crew in charge of the show car forgot to tell Busti to recreate the original paint.

The famous customizer, who despised white cars, figured that Dodge wanted him to give their show car more pizazz, so he went ahead and repainted it in a custom shade of Candy Orange.

When they went to pick up the freshly repainted car, the Dodge crew were enraged because there was no such thing as an orange diamond. But, since there wasn't enough time for another repaint, the car was showcased at the next event, donning the flamboyant finish.

Luckily, the Candy Orange paint was an unexpected success that drew even larger crowds, so the Diamante finished its show car duties in this new guise.

The most valuable Mopar in existence

The one-off was retired from the car show circuit in late 1974, but unlike other concepts that ended up meeting the crusher, the Diamante went into storage.

Four years later, as the Chrysler Corporation was navigating murky financial waters, this exciting HEMI-powered show car was auctioned off.

For the next thirty years, the Diamante bounced from collector to collector until it was purchased by its current Mopar fanatic, Steven Juliano, who later restored the car and repainted it in the original Pearl White Diamond coat.

These days, any surviving 426 HEMI-powered Mopar in good shape is worth a small fortune, but the 1970 Diamante concept is by far the most valuable.

In its August 2012 issue, Mopar Action Magazine called this one-off the "Most Valuable Mopar on the Planet," a title it unquestionably still holds today.

Though it never became Chrysler's answer to the Chevrolet Corvette, the Dodge Diamante remains a fascinating Mopar from the golden age of muscle that deserves to be remembered.

For more information about this forgotten HEMI-powered one-off, we recommend watching the YouTube video below by RETRO CAR.