No

A non-turbo S2 was an S1, while a non-turbo S4 was an S3.  The S1 and S3 were a bit shorter too.

Scott Chatfield

Roger that Scott Thank you !

Roger that Scott Thank you !

@ Daniel Danno164

There are 2 main characteristics to distinguish all 4 types of ALCO swichers: Trucks and seize of radiator grilles.

- ALCO S-1 is of Pre-War origin, has 660hp normal aspirated, small radiator grilles and rode on Blunt trucks.

- ALCO S-2 is Pre-War, has 1000hp by turbocharging, has therefor a larger radiator and larger radiator grilles and rode on Blunt trucks.

- ALCO S-3 is Post-War, 660hp normal aspirated, small radiator grilles and rode on AAR Standard Type A trucks

- ALCO S-4 is Post-War, 1000hp turbo, large radiatior grilles and rode on AAR Standard Type A trucks.

The frame of all the ALCO switchers have all the same lenght differs about 30cm. S-2 and S-4 have a 30cm longer main frame as S-1 and S-3.

Lutz

S1 and S3 are shorter

The S1 and S3 have a 22'0" wheelbase and 40'6" frame (pilot face to pilot face).

The S2 and S4 have a 22'6" wheelbase and 41'6" frame.

Presumably the difference is due to the larger radiators.  Perhaps the generators are longer too.

Scott Chatfield

Blunt trucks and other stuff

While it has nothing to do with the scale model versions, the place where the S-2/S-4 turbo is located, just ahead of the cab under the hood, is occupied with an exhaust muffler on the S-1/S-3.

Way back in the day, I had a regular yard job on the waterfront in Baltimore. My usual power was a B&O S-2 with the Blunt trucks. I would be bopping around the yard enjoying myself because I liked running the Alcos. 

Once in a while, I'd get an ex C&O SW-7 or SW-9 with the AAR trucks. As I started to "bop" around, I'd quickly realize how crappy the tracks down there were. Instead of jaunting, I'd be rocking and rolling. The Blunt trucks absorbed so much of the rough ride that the AAR trucks did not. 

Blunt vs AAR

Yes, the single-equalized AAR-A trucks make for a rough ride, and are hard on loose rail joints, but I gather the reason the Blunt truck fell out of favor is it's a bear to change out brake shoes.  And switchers go through a lot of brake shoes.

Scott Chatfield

@Scott

You are right, the frame lenght differs about 30cm; i have corrected my posting.

Lutz

Thank you everybody this info

Thank you everybody this info is a big help I was wondering why what I thought was an S2 with sound did not sound like what I knew to be an Atlas S2, I have since realized I have an S1...I love the Alco S locomotives and Sw's,  MP15DC,  SW1500...hard to find SW1500..Have a good weekend everybody, thanks again.