The flagship S8 is powered by a new twin-turbocharged 4.0L V8 that generates 520 horsepower and 479 lb-ft. of torque. The 4.0L V8 replaces the old 5.2L V10. The 2012 S8 reaches 0-62 mph in 4.2 seconds and as a electronically-limited top speed of 155 mph. Compared to the old 5.2L V10, the new 4.0L is almost 23 percent more fuel efficient thanks to “cylinder on demand” technology and a start-stop system. The 4.0L V8 is mated to an eight-speed tiptronic gearbox.