This One-Off V-10-Swapped Ford Mustang Avoided the Crusher. It’s Preserved as a 510-HP Middle Finger

• Ford’s Powertrain Research and Advanced Engines team built a V-10-powered concept in the early 2000s.
• Luckily, it escaped being crushed and has now been restored as part of Ford’s Heritage Fleet.
• It’s punchy and still capable of putting 510 horsepower to the wheels more than two decades later.

Over the years, the Ford Mustang has been offered with four cylinders, six cylinders, and eight cylinders. A V-10 stuffed in a ‘Stang? No, at least not in a production model. However, in the early 2000s, a team of engineers at the Blue Oval’s Powertrain Research and Advanced Engines did just that. And they didn't ask permission first.

That car—a silver 1999 GT coupe that had formerly served as a fitment mule for the naturally aspirated 5.4-liter V-8 Cobra R—found itself the recipient of one heck of a transplant. Displacing 5.8 liters, the 10-cylinder engine was completely unrelated to the Triton V-10 found in Ford’s truck applications; it was actually a 4.6-liter DOHC V-8 with two additional cylinders grafted on.

Let’s restate that. The all-aluminum V-10 in this one-off Mustang was made by cutting up sand-casting molds for a 4.6-liter V-8, retooling those molds in a 10-cylinder format, then pouring in the molten aluminum. The motor got some Cobra parts, including connecting rods and pistons, but received its own billet crankshaft and overall weighed some 60 pounds less than the Cobra’s V-8.

Power? Back in 2004, it made about 426 hp at 6500 rpm, a stout figure for its time and capable of running down the dragstrip in the high-11-second range. Best part? The team that built this car didn’t tell management they were working on it; they simply produced it as a fait accompli, the same trick Lamborghini’s engineers pulled on Ferruccio with the prototype Miura. Based on the displacement, the team started calling it the Boss 351.

Unfortunately, Ford is not a small-batch Italian exotic automaker, and it employs plenty of people who make sure the books balance. As it aged, the Boss 351 became the oldest prototype on the books, and to hear some of the original build team tell the story, the accountants wanted it off the books. As in: sent to the crusher.

Thus began a years-long cat-and-mouse game between those who loved this wild one-off and Ford's Vehicle Controls team, who were trying to find out where it had been stashed. Happily, after being tucked away in various hidden corners, the Boss 351 eventually came into the orbit of Ford's Heritage Fleet, who ensured it would be kept safe from being cubed.

Now, the Heritage Fleet team has worked with the original build crew to return this V-10 Mustang back to its original glory. It needed new electronics and a thorough going-over, after which it was strapped to the dyno to see what the numbers said. Like a fine wine, apparently a V-10 Mustang improves with age, pushing over 510 horsepower at the wheels, with a soundtrack halfway between a bar brawl and a Lexus LFA.

As a semi-secret project that survived only thanks to the enthusiasts in Ford's vast corporate structure, this one-of-one pony car has a great backstory. The fact that it's a relatively unremarkable SN95 Mustang with nearly double the power of a contemporary V-8-powered GT just makes it even cooler. Perhaps the best part is that it’s basically a sleeper, nondescript silver on five-spoke alloy wheels, nothing special until it clears its throat.

Should Ford have built a 10-cylinder Mustang? The good news is that it did build at least one. The even better news is that the V-10 Boss 351 is still around.

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Brendan McAleer is a freelance writer and photographer based in North Vancouver, B.C., Canada. He grew up splitting his knuckles on British automobiles, came of age in the golden era of Japanese sport-compact performance, and began writing about cars and people in 2008. His particular interest is the intersection between humanity and machinery, whether it is the racing career of Walter Cronkite or Japanese animator Hayao Miyazaki's half-century obsession with the Citroën 2CV. He has taught both of his young daughters how to shift a manual transmission and is grateful for the excuse they provide to be perpetually buying Hot Wheels.