Each rule has it exceptions.
Back in 1980's 300dt models have been sold with 2.5l engines.

 

I'm sure there are and I do find some exception, but every example I find of the 300DT are 3.0L except for the "300D 2.5 Turbo". In general though, the exceptions seem to be geographic in nature:

E300 BlueTEC was sold as E320 BlueTEC in US, Canada.
E500 was sold as E550 in US, Canada.
E280 4MATIC was sold as E300 4MATIC in Canada.

... or petrol vs diesel:

The E320 diesel models before 2005 had 2.9L engines but the petrol version 3.2L engines

But but the 2011+ E63's have roughly the same engine size as their predecessor which I don't think has been an exception before. The only reason I can find for sticking with the E63 badge is on motortrend.com;

From a marketing perspective, however, falling displacements create a problem, because AMG buyers expect high badge numbers with their high performance. AMG's solution is to set the number 63 as its performance moniker, since it recalls the legendary 300 SEL 6.3 super saloon. The strategy has been in place since the last generation of 6.2-liter V8-powered sports cars, which all had 63 in their names, and will likely solider on with the 5.5-liter twin turbo engines and whatever comes after.

Read more: 2012 Mercedes-Benz E63 AMG First Drive - Motor Trend

 

WTH is an E340?


All I could think as I read this thread was the old axiomatic caution about the use of the word, "ASSUME."

It's the same with every manufacturer, they all fiddle with this to one degree or another.

And not just cars/trucks: My old KZ-750 had a 736cc engine. Should I have sued for misrepresentation?

 

Is this keeping you up at night?

It is all figured out in the marketing department of MB.

 

Bare in mind that engineers had to work on US customer for over 20 years to change the perception on "oil change 3000".
I am trying to keep up with the fast forward changes we do have in last couple of decades, but sometimes it take more than imagination to really feel it.
Few years ago I did own a "monster" 300 HP BMW with V12 engine.
Now 300 HP can be pumped from 6-banger coming off the assembly lane and than some modification can even triple that for racing.
6 seconds car are still impressive for average Joe, but Ken Block drives a car that makes it to 60 in less than 2 seconds.

 

one of the reasons they didnt make it a E55 is because they didnt want a "downgrade" which is totally false because the new 63's are not only 5.5L they are also TWIN TURBO. so it still producing the same, if not more power.