Some cars can put you on edge even before you've been given the key. The Shelby Mustang GT350R is certainly one of them. It looks so tough, with its road-scraping front splitter and its gaping grille open wide like a great white's daggered mouth. It's also rare - the only one in the country - and everything about it, from its suspension settings to its semi-slick tyres, has been developed to work on a sun drenched Californian circuit, not a drizzly old English airfield.
The GT350R is as hardcore and as focused as the Mustang has ever been, more so even than the more road-biased GT350 model. Ford Performance set out to build a Cayman GT4-chaser out of a big old muscle car - which is a bit like trying to make a 110-metre hurdler out of my grandmother - and it's gone to town on the Mustang. Naturally, the springs and dampers are completely reworked while the tyres, Michelin Pilot Sport Cup 2s, are just about as extreme as road-legal tyres get. The rears are so wide at 315mm that they almost meet in the middle, while the fronts, 305mm in width, appear as though they'd require the full strength of Hercules to apply any steering angle to.
Those four fat tyres wrap around carbon fibre wheels. They save almost 6kg of unsprung weight at each corner, which is the sort of weight reduction chassis engineers fantasise about while their spouses are away. Sub-£1m cars just don't use carbon fibre wheels. The rear seats have also been junked to save weight and, if you're really serious about setting PBs and purple sectors, you can do away with the air conditioning and sat-nav. Even so, the GT350R still weighs 1,660kg.
Ford Performance has had a good hard look at the car's aero, too, adding a more prominent front splitter and a bigger rear wing to increase downforce. The vent in the bonnet - it's not a hood - the flat underbody panels, the rear diffuser and the vents in the wheel arches are all there to massage and direct the air over and around the car in the most efficient way possible.
What really demonstrates Ford's ambition for this GT350R, though, is the engine. For as long as there have been stars in the night sky American muscle cars have used big, weighty, relatively lazy cross-plane crank V8s that produce all the torque in the world, while nimble little European sports cars have used fizzy flat-plane crank V8s. They're more compact and they rev higher, which means they're ideal for cars that are going to be driven at the limit and flung through corners.
The GT350R ditches its cross-plane V8 for the flat-plane kind, which really blurs the line between muscle car and sports car. It's a 5.2-litre unit that develops 533hp - at 7,500rpm, in a Mustang! - and 429lb ft. A six-speed manual and Torsen LSD send drive to the rear wheels. Ford quotes a 3.9-second 0-60mph time, which is staggeringly fast for a weighty old thing with a manual 'box.
The GT350R doesn't feel much like any other Mustang inside the cabin. The GT's big, plush, squishy leather chairs have been replaced by heavily-bolstered sports seats, which are also set a little lower. The seating position is just about spot on, although from there the car stills feels rather large. On the plus side, it's finally stopped raining.
What you have to remind yourself when driving the GT350R on track is that, underneath, it's still a Mustang, a car that lives for being driven on track as much as my grandmother lives for the UK's illegal rave scene. (Why am I thinking about my grandmother so much? Must call her). Because whereas the Mustang GT is all at sea on circuit, the GT350R feels right at home. There's a section of track right at the start of the Thruxton lap that includes a fast left hander over an unsighted crest into a heavy braking zone. It would trip up anything that didn't have proper control over its mass, but the GT350R feels completely locked down.
The Cup 2 tyres find lots of grip on the still damp surface, while the steering is sharp and direct. Most tellingly, the car feels 300kg lighter and 10 per cent smaller than it really is, which means you can start flinging it around and flicking it between direction changes like a purpose-built sports car. Ford Performance has engineered most of the muscle car out of the GT350R, and I mean that as a huge compliment.
Church corner - the fastest bend in the UK - is such an unsettling piece of track that at times I wish they'd put a chicane in it. But the Mustang is really composed and settled in there, even well into triple figure speeds. I'm always a bit cynical about the claims manufacturers make about downforce figures on road cars, but in this case, I have to believe the aero devices are doing something.
Against all the odds, the GT350R is a load of fun to drive on circuit. But you know what? If you bolted on a set of sticky tyres and rock solid suspension, then dropped in a 500bhp engine, you could make just about anything this side of an intercity train good to drive on circuit. The difficult thing is making a car that's competent on a smooth, flat track, and also on a bumpy, uneven road.
I haven't tried the GT350R away from Thruxton so I'm not casting any aspersions about how it drives on the road. But it works well out on the public highway will be the difference between the GT350R being a likeable sideshow, and a truly great performance car.
FORD SHELBY MUSTANG GT350R
Engine: 5,163cc, V8
Transmission: 6-speed manual, rear-wheel drive
Power (hp): 533@7,500rpm
Torque (lb ft): 429@4,750rpm
Top speed: 177mph
MPG: 16 (yee-haw, etc.)
CO2: You're joking?