Is this the same engine with a different tune?

SL550 = V8 Twin Turbo

There's more to it than that. The V8 in the W203 C55 is of the M113 family - three valve, SOHC, twin spark heads. If you've ever priced out a spark plug change you know what I'm talking about!

Also found in 4.3L format (various '430' Benzes in the 90s and early 00s, plus the C43 - but with upgraded cams), 5.0L format (the '500's) and of course our favourite, the 5.4L format in AMGs only (but badged as 55). The 55 came both NA and boosted, ie. the 'Kompressor' line of AMGs. Oh, and a heavily revised derivative was found in the SLR McLaren.

Then came the V8s in the '550' cars, DOHC, four valve and I think they went back to single plug heads. 4.7L and 5.5L displacement. These are the M273 motors, which I believe were all NA. These came out in about '05 or so, if I remember right. My dentist buddy had a C55 brand new back in '05, but sold it not long after because he was pissed off that a 'regular' Mercedes motor (the 550) made more power than his AMG.

The current crop of Mercedes and AMG products use another V8, the M278, which I believe is a derivative of the M273, but now with twin turbos and various displacements - but notably using turbos in both Mercedes and AMG format (but still NA in the new SLK55).

So the M273s make more power than the M113s through improved breathing and electronics, and the M278s add forced induction on top of that. Seems turbos are all the rage (again) now - everyone wants more power but less emissions.

MarcusF has a lovely site with plenty of the details, I will link below. I think he had a page about the M113 too, but I can't find it now:

http://www.marcusfitzhugh.com/CLK/index.html#MB

http://www.marcusfitzhugh.com/CLK/opp.html

http://www.marcusfitzhugh.com/CLK/M278.html

Awesome writeup. Thank you!

Forgot to mention, of course, the new motors have direction injection. Anyway, Marcus' site goes into the details, very good reading (and writing from Marcus!)

Even though the newer 5.5NA was around 389hp (?), just a little more than the C55, the programming/mapping has a lot to do with how "awake" the engine feels. I thought I read somewhere that people who compared the CLK550's said that it was definitely a "fast" car, but it wasn't as awake as the C55/CLK55. Still very fast though for a small car.

That's interesting that they would say that. My reading of Marcus' write ups is that the M273 has more torque and earlier in the powerband, so you'd think it would feel peppier than the older M113.

In my C55 I raced a CLK550 and he kept up right with me until about 100.

Your grammar is outstanding.

I actually was thinking how relieving it was too see well-written posts on the internet as I was reading that.

OMG BBQ lol

In all seriousness that was a great description. I imagine the direct injection helps heaps with fuel economy. The SOHC 3 valve heads are great for low end torque but are never going to flow a lot for high end power.

Thank you gents, my grammar had better be good - my day job as a lawyer requires it!