Brabus is the biggest and most famous independent Mercedes-Benz tuner out there and the Germans have been fettling with products sporting the three-pointed star since the late '70s which is why we were not surprised to find out that one of their most powerful creations, the $400,000 Rocket 900, puts out almost 280 horsepower more than the Mercedes-Maybach S650 it's based on. Here's how Brabus does it.

Brabus is known for its land-bound rockets

When Mercedes-Benz decided to revive the dormant Maybach brand for the second time this century, the call was made for it to be merely the badge attached to Merc's ultra-luxurious versions of its pre-existing models such as the G-Wagon Maybach or the longer-than-a-Monday S Class Maybach. The latter is available over here in either S 560 or S 650 trim and, as you'd expect, Brabus chose the latter as the base for the Rocket 900.

Glancing over the technical data, you'd expect the S 560's turbocharged, 4.0-liter V-8 that already produces 463 horsepower and 516 pound-feet of torque to be the prime candidate for a thorough upgrade job since you can easily bump up the power by ramping up the boost in the turbos or swap the existing turbos for heftier ones and it's a more compact unit.

For reference, the base model S Class (in the U.S.) is the S 450 that's powered by the 362 horsepower 3.0-liter, twin-turbocharged V-6.

Brabus also chose to get to work on the S 650 because that's the flagship Mercedes-Maybach model and because it's got quite a bit of experience working on the AMG-built V-12 mills that trace their roots back to the M275 which, in turn, powered the R230-generation SL 600. In that car, the engine, displacing "just' 5.5 liters, put out just under 500 horsepower but, after Brabus was done working on it, the output went up to 730 horsepower. It is no wonder, then, that the much-improved M279 version has got so much to give.

How much is that, you ask? Well, the Brabus Rocket 900's name wasn't picked at random. The 'Rocket' part adds it to Brabus' lineage of Rocket sedans and convertibles - all entirely too powerful highway sling-shots that have claimed many records in their segment over the years - while the 900 is, you guessed it, the power figure.

The way this is done is simple. Actually, it's not at all simple. The only thing that is simple is for us to tell us what Brabus keeps out of the stock Mercedes-AMG engine: the aluminum block, although even that one is modified and lightened. Then the engine is bored out to 6.3 liters (that old SL also displaced 6.3-liters which was even more impressive since the starting point was the 5.5-liter mill).

On top of that, the internals are new (crankshaft and all that) and made in-house by Brabus and the result is a more powerful and also lighter engine. But the engine still has to move around a car that tips the scales at about 5,600 pounds and that's what makes the Rocket 900's 0-60 mph time of 3.7 seconds all the more impressive.

At least after you pay $400,000 for one, you won't spend any more on a chauffeur because this is something you'll want to drive yourself.