NECR Geeps sound like...

Hi all

I was wondering why the New England Central Geeps (GP35 or GP38?) tend to sound like old GP7/9s... even old Alcos! They have a sort of shuffly, rattly, exhausty sound to them that I don't hear on Guilford's EMDs much. I don't know anything about the engines inside all the locomotives...

Am I just hearing things??

JD

GP38's (NECR) will sound different from GP40's (GRS) because the 38's are non-turbocharged, whereas the 40's are, so on the 38 there's nothing else mechanical between the prime mover and the exhaust.

GP7/9's are also non-turbocharged.

Hmmm... that makes sence!

Here is a bit more info on the subject.

The following EMD locomotives use a Roots blower (a type of supercharger):

GP7, GP9, GP18, GP38 (and their SD counterparts)

These ones use a turbocharger:

GP20, GP30, GP35, GP39, GP40, etc (and their SD counterparts)


The B&M 252 is a GP38 (the only one left on the Pan Am roster), and if you ever have a chance to encounter it along with a GP40, it's a good way to hear the auditory differences between a supercharged 645 and a turbocharged 645.

A visual clue is that supercharged EMDs have two (or sometimes four) small exhaust stacks, while turbocharged EMDs have one large exhaust stack.

So a non-turbo is really supercharged? Is that for all the models?

Nell, the turbos on GP40's and the like emit a high-pitched noise, a combination of whistle and scream. A non-turbo EMD will be more like a chug or a chanting noise - I don't know how else to try to put it into words. As MEC 407 says, if you happen to be near both at the same time you'll hear the difference.

I've seen links to ALCO sounds on line - are there any for EMD she could check out?

This site has some good sounds to listen to and compare:

http://trainiax.net/merecordings.htm

In particular, listen to and compare the GP11 (rebuilt GP9), GP38, and GP40. Also worth listening to are the Alco/MLW and GE sounds. All Alco/MLW and GE locomotives have turbochargers, but they are four cycle rather than two cycle and use a different type of turbo, which may contribute to why they sound so different from EMDs.

But are non-turbo engines ALWAYS supercharged? Or "normally aspirated"?

I will have to try out those clips when I get home (yes, playing hooky here at work...)

NellsChoo wrote:But are non-turbo engines ALWAYS supercharged? Or "normally aspirated"?

When it comes to EMD locomotives, yes, all of their non-turbo engines use a Roots blower, which is a type of supercharger. Some people refer to them as normally aspirated but I guess that isn't quite accurate.

How about the SD80MACS?

Also, The Amtrak P42DC's sound unique when idle, mainly with the whoop.

Robert Paniagua wrote:How about the SD80MACS?

All EMD locomotives from the 40 series and higher have a turbocharger.

EMD 567, 645 and 710 series diesels are two cycle engines and need the roots blower to scavenge the exhaust gas from the cylinder. The supercharger is not putting more air in the engine like a turbocharger it is simply blowing the exhaust gas out of the cylinder. A 2 cycle motor fires on every crankshaft revolution and doesn't have the extra exhaust and intake strokes like a 4 cycle motor. Every time the piston reaches the top of its stoke in a 2 cycle engine the cylinder fires unlike a 4 stroke motor that fires every other time the piston reaches the top of the cylinder. When the piston gets to the bottom of the power stroke in a 2 cycle the intakes ports in the bottom of the cylinder walls are uncovered. The blower blows fresh intake air up through the cylinder and expells the exhaust gas out the exhaust valves in the head. I believe in the turbocharged EMD's at certain rpm the turbocharger takes over from the blower and provides boost and exhaust scavenging.

Those older engine are 2 STROKE?? Like some boat motors?? Really? Or am I reading that wrong?

You are reading it right Nell - older EMD's are 2-stroke, not entirely different from your chain saw, LOL.

Even the newest SD70ACe and SD70M-2 are 2-cycle engines. It's not just the older EMDs. It's all of 'em.*


*with one exception -- the ill-fated SD90MAC-H