The new XKR is 20bhp more powerful than the last one and 70 to100 kilos lighter. That means every one of those 420 horsepower is pulling 12% less weight. It's a quick car.
The coupe covers 0-60mph in 4.9sec and the convertible in 5.0sec, and both have a restricted top speed of 155mph.
With 413lb ft of pulling muscle, also an improvement on the last model, and a six-speed automatic gearbox, they are also blisteringly quick to accelerate on the move - 50-70mph takes just 2.5sec.
New air inlets and changes to the valve timing provide the performance increases in the car's supercharged 4.2-litre V8 engine.
As in the standard 300bhp XK, the gearbox has three shift modes - normal, sport and manual. Sport allows a more performance-orientated driving style, while manual lets the driver take control of gearshifts using paddles behind the steering wheel.
The suspension has been made firmer for the XKR and there's a bracing strut between the rear shock absorber towers to make the whole car even stiffer. Faster-acting, weightier steering and more powerful front brakes are also fitted.