When a new supercar arrives, the motor gets the glory. Which is as it should be—anytime an automaker throws big money into designing an exotic spaceframe and 200-mile-per-hour bodywork, it needs muscle to match. The wrong engine, meanwhile, can sink a supercar's reception and reputation (look at the Jaguar XJ220 for a lesson in how a whole car suffers if it's got a weak heart). Aston Martin can't be accused of skimping on the heart of its new halo car, the $3.2 million, out-of-this-world Valkyrie. The new supercar's motor spins out 1,000 horsepower on its way to an 11,100 RPM...