Two tuners companies are racing to create the fastest Mercedes C63 AMG – US-based Renntech and German legends Brabus.

The standard Mercedes C63 AMG pumps out 457bhp from its brawny 6.3-litre V8 engine and accelerates it from 0-62mph in just 4.5 seconds.

But now Renntech and Brabus have built modified Mercedes C63 AMG’s which produce more than 500bhp.

Renntech

By fitting a high-flow stainless steel exhaust Renntech has liberated more punch from the engine and an even louder and throatier exhaust note.

These mechanical changes have been backed up by a recalibration of the engine’s computers to produce a total output of 548bhp.

Pulling power is also boosted to 510lb/ft – 40lb/ft more than the 7-litre Corvette Z06 supercar.

And to harness the extra momentum Renntech has fitted adjustable suspension and bigger brakes.

View more images of the Renntech C63 AMG

Brabus

Brabus has a long history specialising in Mercedes modification and its B63 S Performance Kit looks like a polished product.

Standard power rises by more than 70bhp to 530bhp and pulling power is up to 479lb/ft.

And Brabus has released performance figures to whet customers’ appetites: 0-62mph is dispatched in 4.1 seconds (down from 4.5) and 0-124mph takes 13.1 seconds (down from 14.5).

On derestricted Autobahns the Brabus Mercedes AMG C63 can now reach an astonishing 197mph – the 155mph articificial speed limiter fitted by Mercedes has been removed.

View more images of the Brabus C63 AMG

Like Renntech, Brabus has concentrated on exhaust tuning and tweaks to the engine’s computer to gain this massive performance increase.

Adjustable suspension, bigger brakes, Brabus 19-inch wheels and many interior options complete the B63 S Performance Kit.