When you mentioned that the displacement of your W 123 240 D (newer version)
was 2376 cc, it confused me because that is neither the real displacement (2399
cc) nor the tax displacement (2350 cc). That was the tax displacement of the
older 240 D, but since you didn't mention it, I thought you had just made a
mistake in your car's real displacement. Then when you stated your method of
how the model numbers are arrived at, I thought you meant the real displacement
and not the tax displacement (since you never mentioned tax displacement in
your explanation). That is why I pointed out all those models whose
displacements are a few cubic centimeters over what the model number indicates
(e.g. the 4520 cc model 450) that according to you, by rounding up would give
model numbers MB does not use. For example, the 450 would be 460, the older 240
D at 2404 cc would be 250 D, etc. I thought you were referring to the real
displacement, not the tax displacement.
Now that you gave the longer explanation and that I see you used tax
displacement on purpose, I made my own calculations of real displacement and
tax displacement according to the Steureformel you gave me a few years ago. I
found that there are exceptions to both methods of naming models whether by
real or tax displacement. Whether you just round the real displacement up or
down to the nearest 100 cc or you round the tax displacement up to the nearest
100 cc, there are models that will not work.
Some model numbers do not work according to either method. They are exceptions
to the rule made on purpose by MB because MB wants a certain number on the
trunk lid. For example, the 5.8-liter V12 which is model S 600, the old 6.9
(both real and tax displ show 6.8), the current 1.8-liter models C 200, etc.
Some models do not work according to your method. For example the current 4.3
liter, with 4266 cc of real displacement and 4196 cc of tax displacement. It is
called 430 (according to real displacement) and not 420 (according to tax
There are also some exceptions to the real displacement rule that do work with
the tax displacement rule. For example, the 55 AMG models whose real displ is
5439 and Steuer 5401. According to my method, they should be 54 AMG models, but
according to yours they are 55 AMG as MB names them.
The problem is that with many models which do not work according to one of the
methods, you can defend the validity of your method by coming up with an
explanation as to why it's an exception. You did it with the 6.9. Here's one to
defend my method. The old M 110 DOHC inline-6 had a real displacement of 2746
cc and Steuer 2717 cc. According to my method it should have been model 270.
According to you it should be 280, which it was. This does not automatically
mean that the model number is based on the Steuer displ. The history of that
model number is that the old M 130 engine (2778 cc and Steuer 2748 cc) was
named correctly 280 according to both methods. MB reduced the cylinder bore 0.5
mm for the new M 110 engine. There had been many models named 280, e.g. 280 S,
280 SL, etc. MB simply wanted to keep the 280 designation and not switch to
270, so that the newer models would not seem inferior. Thus, they called the
models powered by the M 110 engine 280 also even if their model number system
is based on real displacement. This was simply and exception (like the 6.9).
Overall, I realize that there are many more exceptions using my method than
yours, so it's very possible that you are correct.
Did you read anywhere that the method of naming the models is indeed based on
rounding up the Steuer displacement, or did you just figure it out by observing
the model numbers and comparing to the real and Steuer displacements?
Also, if you'd like my calculations of all the displacements going back to the
Mercedes and Benz merger, I'll email them to you directly.