The recently launched Mercedes CLS 63 AMG is powered by a 5.5-liter
biturbo V8 engine that delivers a total of 518 HP and 516 lb.-ft. of
torque - a very impressive output for a luxury sedan, no doubt. That
being said, American tuner, Renntech, has found a way to further improve
the final output of the car to an impressive 669 HP and 734 lb-ft of
torque.

According to the first details offered by the tuner, this is just the
Stage 1 upgrade for the CLS63 AMG. In this stage, the extra output is
provided by the addition of ECU tuning software and a new exhaust
system. This allows the Mercedes to sprint from 0-60 mph in 3.4 seconds
at a speed of 125.01 mph. Better yet, it recently took on a Nissan GT-R
at the Palm Beach International Raceway where it achieved a quarter mile
in 11.21 seconds at 126 mph.