From its debut to a public who waited with baited breath to catch their first glimpse of it at the World’s Fair in 1964, the Ford Mustang has always been popular with tuners and petrolheads looking to extract as much muscle as possible from America’s premier steel bicep.

Virtually every big-name tuning house in the world has taken a stab at the ‘Stang, from Saleen to Hennessey Performance, but of all those there’s one name that stands out above the rest: Shelby.

It’s a little ironic that while the original Mustang offered aggressive sports car styling and a big V8, it was actually built from a medley of leftover parts. Sure, it looked the business but underneath it wasn’t actually all that much of a sports car. Even the current Mustang is a big lump of pig iron with a big lump of an engine sitting out the front, and compared to the best sports coupes and super-saloons around, it seems a bit… basic.

Not so with the Shelby GT350R. A stripped-out, ‘roided-up track special, if the Mustang is Rocky Balboa then the GT350R is Ivan Drago, a pure-bred apex predator designed for one thing and one thing only: absolute domination on the race circuit.

Performance

Most excitingly of all, and key to the both the GT350R and its more road-oriented sibling the GT350, is a very special new motor. While the stock Ford Mustang uses a 5.0-litre V8 famously referred to as the ‘Coyote’ motor, the GT350R gets an engine that’s very different from any other V8 that Ford makes.

Called the ‘Voodoo’, it has a 5.2-litre displacement and a flat-plane crankshaft, the same type of engine construction used in Ferrari’s V8-engined Formula One cars. The result of that flat-crank design means that the Voodoo can rev higher and harder than a standard V8, making for a car that sounds very different and goes very different to practically any other muscle car.

In terms of numbers, the GT350R generates a maximum of 526bhp and 582Nm of torque and redlines at an absolutely phenomenal 8,250rpm.

That makes it the most powerful naturally-aspirated V8 that Ford has ever made, and in a word the acceleration is absolutely ballistic. That hyperbolic amount of power goes straight to the rear wheels via a heavy-duty Tremec manual gearbox, which has been almost entirely reworked to ensure it can cope with the sheer output of the Voodoo engine.

As a result, the GT350R can wallop its way to 62mph from a standing start in just 4.4 seconds, which makes it faster than the likes of a Lamborghini Gallardo, a 997 GT3 or a V8-powered Audi R8 Spyder. To use that oh-so-American benchmark of speed, the quarter mile, this thing will do it in 11.96 seconds before hitting a top speed of 155mph.

Even if you’re nowhere near the car, you’ll know all about it courtesy of the most obnoxiously loud exhaust note this side of an open-header Harley Davidson with a muffler delete. To say the GT350R is noisy is the understatement of the century, but that’s hardly much of a complaint.

In standard mode the exhaust note will go from loping V8 idle to baleful scream as it nears its stratospheric redline; flick the switch to engage loud mode and the cannon-fire blasts out of the twin tailpipes will rattle the fillings of everyone within a two-mile radius. If you can’t tell, we rather liked that about it.

Ride and handling

Now, we know what you’re all thinking: ha-ha-ha-Mustang-all-torque-no-traction-cars-and-coffee-ha-ha, or something along those lines. But, while straight-line performance has always been a muscle car hallmark, it’s the way that this car matches insane power with uncanny agility that really sets the GT350R apart.

We tested the car exclusively on Thruxton racing circuit, a two-and-a-half mile stretch of tarmac that’s widely regarded as the fastest circuit in Britain; perfect territory for a 526bhp all-American track toy.

The beauty of the Thruxton circuit is that not only is it incredibly fast, it can also be incredibly demanding of a car, with several of its corners combining crests, camber, heavy braking zones and deceptively tight turns all at once.

That would baffle many more agile cars than the Ford Mustang, but only serves to highlight the incredible work that Shelby has put into creating the GT350R, which really does feel lightyears ahead of its 5.0-litre cousin.

It used to be that the best way to drive a Mustang fast on track was to use big stabs of throttle to break the rear loose, rotate the front of the car towards the exit of the corner and then thump out in a straight line. However, with the GT350R you can afford to be much more finessed.

The steering is a joy to use with plenty of feedback, grippy Alcantara covering and direct, accurate action while the massive 15.5-inch brake rotors and six-piston calipers bite hard to scrub off speed with vicious efficiency, all the while resisting fade well and being easy to modulate throughout all of the pedal’s travel.

Considering that the standard Mustang is a bit of a lump, the chassis of the GT350R feels brilliantly transparent, while a huge bespoke aerodynamic kit helps to press the car down into the tarmac and really exploit all of that awesome torque.

Along with the huge front splitter, the GT350R also gets a sizeable carbon fibre wing, which actually generates more downforce than the current 911 GT3. Particularly through the faster sections, that aero package and the standard MagneRide suspension really helps to keep things stable and affords the car more grip than you’d ever have thought possible from a Mustang.

Really, the only thing that reminds you of the stock from which the GT350R is bred is the meaty Tremec gearbox. Shifts take a considerable amount of forearm heft, which makes the regular Mustang feel ultra-macho, but which can hamper the GT350R particularly in corners which require rapid downshifts.

It can be notchy to use and easy to miss gears if you're not used to it, but at the same time it’s a nice reminder of the car’s sheer brutality. It might be as far away from the classic muscle car as is possible, but the GT350R is easily the ultimate expression of American muscle for the modern era.

Interior and equipment

The original Shelby GT350 focused on three things: light weight, big power and big brakes. It’s much the same story with the modern iteration, except that the GT350R goes one step further.

Like the standard GT350, it gets an injection-moulded carbon fibre front end to drop weight, but it also loses its rear seats in favour of two carpeted dimples big enough to fit your racing helmet and not much else. There’s no air con and no radio either, while the car comes with the option of ultra-light carbon fibre wheels built using technology developed for the NASA Space Shuttle programme. More on that here.

‘Basic’ is probably the best word to describe it, as even though it comes with the option of an infotainment touchscreen running Ford’s latest SYNC 3 system, the interior is all dull black plastics as opposed to the metal switchgear of the standard Mustang. The finishing touch comes in the form of two huge bucket seats with large side bolsters that sit a few inches lower than the standard ‘stang seats.

Don’t let anyone ever tell you that track-special cars can’t be practical, however, as although there are no rear seats it preserves the same 408-litre boot as the regular Mustang. According to one of the track instructors along with us for the day that’s where you keep your guns’n’moonshine, but it’ll also take suitcases, shopping bags and golf clubs just as easily if you’re feeling a little less, er, stereotypical.

Cost

The Shelby GT350R is priced from approximately $65,000 in the US, which equates to roughly £50,000 according to current exchange rates.

Compared to other track-special cars of similar size, power and pedigree that makes it something of an absolute bargain, with cars like the Porsche 911 GT3 RS and the Nissan GT-R Nismo both coming in at more than three times the Shelby’s asking price.

Of course, the problem is that Shelby currently doesn’t sell cars here in the UK. That means that in order to get one you’ll have to have it imported from the US, which will likely involve mountains of paperwork, huge tax and duty expenses and, of course, the steering wheel being on the wrong side.

Verdict

Violently quick and yet with an uncanny ability to chew up and spit out a track like the best of Europe’s performance saloons, in the GT350R the Mustang has performance as mythical as the legend which precedes it.

While the regular Mustang is a lazy, torquey bruiser the GT350R is more akin to a purpose-built European sports car, with a high-revving engine and one of the best chassis setups ever fitted to a muscle car.

The only real problem is that for us here in the UK, anything with a Shelby badge is essentially forbidden fruit. But, if you’re determined enough to have one imported, in return you’ll have access to what’s arguably the best version of the Ford Mustang ever built. Worth it? Worth it.