The M's, I's, AC's, etc.

[Anonymous]

What do the designations on locomotive models such as "M" "I" "X" etc. mean. I was looking at some BN GP40s which were rebuilt to be GP40Ms however I see no difference in the pictures. These are the said photos: http://archive.trainpix.com/BN/EMDORIG/GP40/3029.HTM and http://archive.trainpix.com/BN/EMDRBLD/GP40M/3507.HTM I was thinking of kitbashing a GP40 but I don't see what I would have to change besides the road numbers. This question does not apply to only the "M" but all those other extra letters.
Thanks,
Reed

[Anonymous]

The "M" stands for MODIFIED (rebuilt locomotives), the "I" stands for Isolated Cab ( in essence, the locomotive cab is isolated from the locomotive frame providing a smoother and quieter ride. The "X" stands for experimental, like the SD40X, SD45X and GP40X (test beds for the SD40-2, SD45-2 and the GP50).
Ch

[Anonymous]

And as far as details go, that really depends on the prototype. Alot of the "M" models have interior upgrades with only a few minor external details like horns, A/C units, lights, etc. different from the original engine.

---jps

[Anonymous]

External distinguishing feathers of the "X" series locomotives are flared radiators similar to the SD45s. Only the SD40x was externally an SD40.
Ch

[Anonymous]

QUOTE: Originally posted by psngrtrn

External distinguishing feathers of the "X" series locomotives are flared radiators similar to the SD45s. Only the SD40x was externally an SD40.
Ch

Actually, that just applies to the GP40X. The GP39X radiators weren't flared, but had a radiator layout very similar to the GP49 and GP50.

---jps

[ckape]

Most of the letters are applied not by the builder but by the individual railroad, so there's all sorts of inconsistancies. The following list applies to EMD locomotives

M most commonly means modified cab, as in a comfort cab with the wide nose, although it seems to man something else on the pictures you pointed to, probably just that it's a rebuild.

I means isolated cab, at least when applied to an SD70 or 75, the SD80s and 90s come with this standard. An isolated cab means taht the cab is structurally isolated from the frame of the locomotive to deaden vibrations. You can spot these by the seam on the nose.

AC means that the locomotive uses AC traction motors instead of DC motors, and is commonly used on locomotives with the wide cab to make a MAC.

B is used to denote a cabless unit, not including slugs.

For GE units the only suffixes I'm familiar with are B and C which denote 2 and 3 axle trucks, respectively.

[nfmisso]

QUOTE: Originally posted by ckape

AC means that the locomotive uses AC traction motors instead of DC motors, and is commonly used on locomotives with the wide cab to make a MAC.

Not always. For example, a GP38AC does not have AC traction motors, it has an alternator instead of a generator to power the DC traction motors. The straight GP38 has a generator. Most (all?) GP38-2 have alternators. The MP15 (aka MP15DC) and MP15AC also both have DC traction motors.

The suffixes mean different things on different models of locomotive.