5 Factory-Built Twelve-Cylinder One-Offs Based on Regular Production Models

Throughout the decades, several manufacturers have conducted experiments that involved stuffing a large motor into the engine bay of a production car that wasn't initially conceived for the respective unit.

Whether this was done to test an engine conceived for a model not yet developed or just for show, it often resulted in some insane cars that made jaws drop to the floor.

Though there are many noteworthy examples of such automotive Frankensteins, we chose the five most spectacular twelve-cylinder-powered mutants that you probably never knew existed.

Pontiac Firebird Pegasus

In 1970, Chevy designer Jerry Palmer was tasked with sketching some future exterior enhancements for the just-released second-gen Camaro.

One of the sketches Palmer drew, which included cues from the 1958 Ferrari 250 Testa Rossa, drew the attention of GM Vice President of Design Bill Mitchell, who decided to turn it into a real car.

However, since the Chevy styling crew was busy with other projects, Mitchell passed the task to Pontiac's design team, who implemented Palmer's modification on a 1970 Firebird - the second-gen Camaro's twin.

The story goes that this endeavor turned into Mitchell's pet project, and the styling chief decided to add "a bit" more Ferrari flair to the Firebird-based concept.

Therefore, he sourced a genuine 352-hp Ferrari V12 and tasked the engineers to stuff it between the Firebird's shock towers.

Miraculously, they managed to do it without stretching the chassis. Nevertheless, the firewall was moved nine inches towards the interior, and the engine's exhaust headers were modified.

Dubbed Pegasus, the Ferrari V12-powered Firebird took on show car duties for a time, and then it became Mitchell's personal car.

This fascinating one-off is still around and can be admired at the corporation's Heritage Center in Sterling Heights, Michigan.

Ferrari 348 M3

Released in 1989, the 348 was Ferrari's latest mid-mounted V8 weapon. Powered by a 3.4-liter Tipo F119 that made from 296 hp to 316 hp (depending on the model year), it was a popular model that sold in over 8,800 examples worldwide until it was replaced by the F355 in 1995.

Several of those examples were kept by the Italian manufacturer, and three lucky 348s were involved in the development of the Enzo supercar.

Codenamed M1 and M2, with the M standing for Muletto (test mule), the first two 348s were used to test suspension components for the Enzo as well as its Graziano six-speed automated manual gearbox.

However, the third, christened M3, became the first and only 348 to be powered by a V12.

After developing a functional prototype of the Typo F140 motors, the Ferrari engineers took a stock 248 and extensively modified it to make room for the Enzo's V12.

The car received a new rear subframe, longer quarter panels, a new rear window, and a custom rear bumper.

Seen roaming around on the roads of Maranello in the spring of 2000, this elongated 428 raised some eyebrows, but few suspected it hid an experimental 6.0-liter V12 capable of nearly 650 hp.

Unlike other similar test mules, the 348 M3 wasn't destroyed. It was in storage until 2005 when it was auctioned off alongside the 400th Enzo.

Chevrolet Corvette ZR-12

Introduced in 1990, the C4 Corvette ZR-1 became a feared supercar killer thanks to its Lotus-engineered LT5 DOHC aluminum V8.

At the time of its introduction, the King of the Hill was the quickest, most potent American production car. However, Dodge's upcoming Viper was about to dethrone it.

Once the Viper hit the streets, several members of the ZR-1 development team decided to create an antidote for the venomous Dodge.

Since they knew management would never fund their wild idea, the team managed to secure some money by claiming they had to run durability tests on the ZR-1 gearbox.

That was partially true, but the team omitted to inform decision-makers that they were about to build a V12 to see what the ZF six-speed transmission could handle.

In the end, the crew took a ZR-1, modified it, and added a humongous V12 under the hood. Initially built for marine and aviation use by Ryan Falconer Racing Engines, the all-aluminum 9.8-liter was modified to work with the ZR-1's transmission and delivered a whopping 686 hp.

Nicknamed ZR-12, this crazy one-off never made it into production, but management deemed it cool enough to keep, so it's still around today as part of the GM Heritage Collection.

Volkswagen Golf GTI W12-650

In the fall of 1975, Volkswagen unveiled the GTI, a sportier version of its popular little people mover.

The GTI was a hit from the get-go, and over the next seven Golf generations, it became one of the most popular hot hatches on planet Earth.

Throughout the lifespan of the nameplate, the production versions of the GTI were never powered by an engine with more than six cylinders but in 2007, VW developed a wild concept that featured a huge motor with twelve cylinders.

Built to wow the crowds at the famous VW festival held in Wörthersee, Austria, the concept was an Mk5 GTI like no other.

Apart from the bespoke body kit that made it stand out from a mile away, it distinguished itself from any other GTI thanks to a mid-mounted W12.

Borrowed from the Bentley Continental GT, the 6.0-liter was rated at 642 hp and, as you can imagine, required extensive modifications to fit in the back of the Golf.

Apart from the engine, the one-off Golf GTI W12-650 was equipped with a rear brakes from the Lamborghini Gallardo, the front brakes from the Audi RS 4, and the gearbox from a Volkswagen Phaeton.

BMW X5 Le Mans

In 1999, BMW managed to win the famed 24 Hours of Le Mans endurance race for the first time in history.

That year also marked the release of the BMW X5 SUV (or SAV, as BMW called it), which was another first for the Bavarians.

A year later, the company decided to celebrate both firsts with arguably the craziest concept to don BMW badges.

Called X5 Le Mans, this special X5 unveiled at the 2000 Geneva Motor Show looked quite ordinary, save for the golden BBS wheels.

However, ordinary was the last thing it could be associated with since it was powered by none other than the Le Mans-winning V12 LMR's race engine.

An epic 6.0-liter, the motor was narrower than the V8 available on the production X5, so it fitted snuggly into the SUV's engine bay.

The only modifications that the race motor received was a carbon-fiber intake and a straight-pipe exhaust that improved output to a jaw-dropping 700 hp.

While the current high-performance M Competition version of the X5 approaches that figure, the 24-year-old X5 Le Mans concept remains the most powerful SUV ever built by BMW.