Clarkson takes out the Roush Mustang and the Shelby Mustang out on a test drive. The Roush Mustang adds a supercharger to the existing 4.6 liter engine that takes horsepower up from 300 to 415. The Shelby Mustang adds a bigger supercharger than Roush’s giving you 475 horsepower. Even then, the Roush Mustang seems to impress Clarkson more than the Shelby. Of course, Clarkson then goes on to race the car against the British Lotus.