RENNtech has been offering performance upgrades to Mercedes-Benz and AMG models for almost 30 years and its decades of experience shows in the latest upgrade kits for the Mercedes AMG E63 and E63 S. In the US, Mercedes wisely decided not to offer the puny base E63. Instead we have to make do with the top-spec E63 S trim in either sedan or wagon body styles. In standard form this potent luxury missile already punches out 603 hp.

The RENNtech R800 Performance Package takes the power levels up to an even 800 hp. It's no simple ECU upgrade either, there are mechanical upgrades too such as new turbochargers that help ensure that the car remains reliable and drivable in everyday conditions. The entire package also meets strict approval standards. The upgrades to the 4.0-liter twin-turbo powerplant mean that torque is up from a serious 627 lb-ft a to a very serious 774 lb-ft, limited to that peak to protect the rest of the drivetrain. The top speed limiter can be lifted too depending on the speed rating of the tires being used. When it comes to power, more is always better.

For those wanting that little bit extra, optional ceramic-coated downpipes with sports catalytic converters help liberate a further 20 hp from the engine. The upgraded exhaust system also turns the snarling V8 soundtrack into a shrieking scream, although that's only in the more aggressive Sport settings. In Comfort mode the RENNtech E63 S remains almost as subdued as the original.

While there are no official figures on the improvements over the standard car's 3.4-second 0-60 mph effort, an example with all available RENNtech upgrades, giving it an even crazier 843-hp, achieved a supercar shaming quarter-mile time to become the world's fastest E-Class. Check it out in the video above.