Ok so all new V8 engines are 4.6-4.7L Twin Turbo

E, CLS 550 402 HP

S, SL 429HP

2013 GL 550 same as S class

2013 GL 450 362 HP

2013 GL450 "...continues to use a 4.7-liter, DOHC V-8, but it's far different than before. This new engine is part of Mercedes' new family of direct-injection, twin-turbocharged V-8s, and whips up 362 hp from 5000-6000 rpm, and 406 lb-ft of torque from 1500 to 4000 rpm". (from motor trend)

Are these different engines or all the same just tuned differently?

 

I would assume that they are all the same, just tuned differently

 

Who cares? You got what you got. I would think it is just different tunes, although, the higher output motors could possibly have more robust parts. Next time you are at your dealer, stop by the parts department and see if there is a different part number for things like turbos, pistions, valves, etc.

 

All the same motor, just different programs and mapping through the computer. The 429hp tune is in the S, SL like you said but also in the CL. These cars are a bit heavier so require some extra hp to perform like the 402hp tune in the E and Cls. These new motors are real easy to make more HP(change the tune) compared to the older NA engines. Aftermarket companies will be making a fortune on tuners.