ok, a lot of misinformation going on here:
1. merc v12s only started being bi-turbo since 2003. it started with the s600/cl600/sl600 5.5l v12 (not 6.0l) making 493hp. this engine is further revised for the maybach to develop 543hp. in the same year, amg introduced a larger bi-turbo v12 making 612hp. as a sidenote: it has taken bmw 7 years to have a proper counter to the s600's biturbo v12. and until now, no bmw car has an engine that overpowers the 65 series amgs. to this day, very few production cars out-torque these amgs....
2. prior to 2003, the w220/c215/r230 models from 2000 had the 5.8l v12 making 362hp. this v12 had cylinder deactivation.
3. before 2000, starting from 1991, mercedes had a n/a 6l dohc v12 originally making slightly over 400hp and was slightly detuned to 389hp soon after. this was the first post-war v12 from mercedes. amg had a 7.3l v12 introduced in the 90s and was fitted into the sl73amg. this engine has been further refined and now is being used as the engine of the pagani zonda. aside from this engine, amg had various other v12s made through the years (in very small quantities). the original s63/cl63 w220/cl215 cars introduced early into the 21st century actually had 6.3l v12s making 444hp. however, all these engines were always based on mercedes v12s.
4. aside from the bi-turbo v12s, amg has had made other force-induction motors. the most famous is the 5.5l v8 used anywhere from the w211 e55 to the slr mclaren. this engine made anywhere from 476hp to over 620. this engine was well-known for its unmatched torque figure and unmistakable exhaust note (ever hear an slr go by? it's so different than other exotics.) amg also had the 3.2l supercharged v6 fitted into the c32 and the slk32. again, these engines were based on regular mercedes motor with the corresponding cylinder count.
extra info:
5. the amg 6.2 is the first amg motor to be completely designed from scratch by amg. this is why this motor has no similarity to the current merc 5.5 v8.
6. the upcoming 5.5l bi-turbo v8 will be the second motor to be completely developed by amg.
7. mercedes is no stranger to force induction; they were the first manufacturer to introduce supercharging to the automobile.
8. the 6.3 moniker has always been special to mercedes as prior to the 90s, their largest motor mercedes had was a 6.3l v8. the legendary 300 sel amg used a 6.3l engine and was the inspiration for the new s-class amg concept featuring the new biturbo v8.
original amg s-class:
http://bp3.blogger.com/_UYUyHACXkrA/...EL+6.8+AMG.jpg