Renntech has been working on a new turbocharger upgrade package for the 4Matic cars. Changes include a bigger custom turbine shaft, different compressor wheel, and different software. An official announcement on this new M157 turbo upgrade package is coming but Renntech previewed on the BenzBoost Mercedes AMG Performance forums that this package is showing over 850 horsepower:
That is at the crank mind you and not at the wheels. Still, the increase over stock is impressive especially the area through the curve from 2500 rpm on. A BenzBoost member in Russia is already running a pre-production version of this turbo package with some custom changes and he has shown some impressive results.
Take a look at his E63 AMG S 4Matic pulling away from a Lamborghini Aventador on the highway as well as a tuned Nissan GTR and a supercharged C63 AMG. The updated Renntech M157 turbo package certainly looks potent.