There was a time, not long ago, when the jumble of silver numbers and letters on the back of a German car meant something. But nowadays those alphanumerics mean nothing, because marketing has become more important than honesty.
In the past, everything had an order. An S430 had a 4.3-liter V8 and a 325i was a fuel-injected 2.5-liter inline-6. Even when the engines were smaller, they didn't hide anything from us. If there was a small turbocharged inline-4 under the hood, they just added Kompressor or 't' to the name.
Then carmakers, in pursuit of fuel economy, started downsizing their engines, leaving them with a challenge: How do you downsize the name?
Take the mid-2000s 3-series BMW. The 330i and 335i both had the same displacement 3.0-liter inline-six The difference being that the 35 was turbocharged. So why not name the pair the BMW 330i and the BMW 330ti? We blame marketing departments pandering to weak egos.
When the engine in the bread-and-butter Merc S-class (the big V8 one) went from a thirsty 5.5-liter to a more efficient turbocharged 4.6-liter engine, Mercedes didn't change the name to S460 Kompressor. That's because, in the German's eyes, someone owning an S550 doesn't want to "downgrade" to an S460 (disregard the fact that the 4.6 liter has more power). And the driver of a 2011 328i (with the 3-liter) apparently doesn't want to buy a new 2013 320ti, even if it has more power and is far more economical.
Even more egregious is AMG. The recent AMG 63s were actually 6.2 liters — an admittedly historical nod to the original 6.3-liter engines from the brand's original Q-ship sedans. Why not really do justice to the brand and just make the engines slightly larger?
Now Mercedes is back to 5.5-liter turbocharged engines which should now be labeled 55 Kompressors again. But don't mind what's really under the hood, Mercedes will still let you assert your superiority with an E63.
And let's not even start on the letters. The designation S-Class is derived from Sonderklasse, or "special class," SL stands for "lightweight sport," and G-Class came from Gelaendewagen. What the hell does GLK stand for? The E-Class coupe is actually based on a C-Class, and the CLS is a member of the E-Class family. The X6 isn't an SUV based on the 6-series, and the 5-series GT has more in common with the 7-series.
Part of this naming confusion absolutely comes from the frankly insane proliferation of the German lineups, but it also comes from a lot of "market consultants" and a regular old lack of concern for order and organization, not something you'd expect from the country that's famous for its efficiency.