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UPDATE: Just to prove that it's got the goods, GM has released a video of its new supercharged Corvette stretching its legs to a massive 205mph (330km/h) top speed. At a time when car makers are showing off every imaginable fuel-saving gizmo, General Motors does the math on the 6.2-litre V8 engine in its new Chevrolet Corvette ZR1 and comes up with more oomph than it expected. The company's powertrain gurus found that the LS9 engine cranks out 476kW (638bhp) - 20 horsepower more than the estimates they made when GM took the covers off the ZR1 before Christmas. Simply, the engine is rated at 76kW (103bhp) per litre of displacement or 1.7bhp per cubic inch (6.2 litres is equal to 376 cubic inches). All that power will push the Corvette ZR1 to a top speed of more than 322km/h, says GM. And torque? The revised official figure is now 810Nm. The key to power and torque is a Roots-type supercharger with four-lobe rotors that sits atop the LS9 engine. A liquid-to-air intercooler is integrated into the supercharger's housing. The engine will be hand-built at GM's Performance Build Centre in suburban Detroit, the same plant that hand-builds the LS7 V8 used in the Corvette Z06.