Both use the same 3000 HP EMD prime mover - the GP40 has 4 powered axles, the SD40 has 6 powered axles. The SD40 frame is long to accomidate the longer 6 wheel trucks.
Never too old to have a happy childhood!
zkr123If there a difference between GP40s and SD40s
Any EMD locomotive with a model designation that begins with "GP" has 4 powered axles (in two trucks with 2 axles each i.e a B_B wheel arrangement)
Any EMD locomotive with a Model designation beginning with "SD" has 6 powered axles (in two trucks with three axles each i.e C-C)
Just to confuse things EMD is currently offering a variant of it's SD70ACE unit with only 4 of the 6 axles powered, 2 are idler axles making a B1-1B wheel arrangement but the model will retain the "SD" designation..
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
Let's talk GP40-2 vs SD40-2:
They are the same except the SD40-2 has:
two more traction motors
HTC (or Flexicoil) trucks instead of Blomberg trucks - to accommodate the extra motors
a longer frame (to accommodate the trucks and a somewhat larger fuel tank)
A ballasted frame (heavier bottom plate) to give roughly the same weight per axle
some extra switch gear to allow series/parallel motor connections to the main generator at lower speeds (puts those extra motors to use!)
larger dynamic brake grids to allow braking force to be generated by those extra motors.
That's about it. So, why would a railroad buy an SD40-2 instead of a GP40-2? The performance is identical above 20 mph, but below that, the SD40-2 can haul more - up to 50% more.
If you have a relatively flat RR and you want to run fairly fast freight, you'd buy GP40-2s. (Conrail bought a lot of these for moving intermodal trains on the old NYC "Water Level Route".) If you are running coal trains up mountain grades, they you'd want SD40-2s. (Conrail bought a lot of these for general merchandise service and coal train traffic over the old PRR. That's a bit of an oversimplification, but the general principles are true.)
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Here is an interesting anecdote about the Rio Grande and the difference between "SD" locomotives (originally Special Duty) and GP ("General Purpose", though that distinction doesn't tell you much). From what I recall on most railroads, the crews called them by their number series, i.e. on the Santa Fe SD40-2s were generally called "fifty-one hundreds". But not on the Rio Grande, on the Rio Grande six axles were called SDs, probably becasue their number series ran together. I.e. SD9s, started at 5300 to about 5315 or so, followed by SD45s through to about 5340 ( I don't remember the cutoff anymore), and then SD40t-2s up through 5450 or so, and then SD50s started at 5500. The Rio Grande was all EMD, and assigned tonnage based upon whether a train had a certain number of "SDs" (as has been explained, six axle units) or GPs (four axle). When the Rio Grande's owner, Phillip Anschutz, bought the SP and merged them it meant that GE units were introduced, which aren't called SDs or GPs becasue that is an EMD name (like "Impala" is a GM name). Later, SP bought a few hundred six-axle GEs (that were not liked on the old Rio Grande). Anyway, once around 1995 or so I overheard a conversation on the radio, the dispatcher was trying to determine if a train had a sufficient number and type of units on a train heading up the hill and kept asking the engineer "are those units SDs or GPs?", which frustrated the engineer becasue they were new GEs and weren't called that. He was trying to explain, well, they are six-axle units, but the dispatcher kept interrupting and asking "yes, but are they SDs"?
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Will DavisTo allow the GP40 to perform in drag service, to improve adhesion and to make it compatible with lower output (older) units it limits its output at low speeds.
Compatible, yes. Improved adhesion, no.
What is did was gradually derate the GP so you could mix GPs and SDs and get the most out of the SD. If you didn't have it, you'd limit the consist to the equivalent performance of all GPs.
GE's version is called Power Matching
So answer me this.
Why did the pre-Amtrak railroads, Amtrak itself, and Metra itself initially go with 6-axle power -- the SDP-35 (2500 HP), U28CG and U30CG, SDP-45 and FP-45 (3600 HP), the ill-fated SDP-40F (3000 HP -- gave up on the 20 cyl engine) along with the 6-axle GE P40C's, and last but not least, the F40C?
Does a passenger train need lugging power below 20 MPH? If you gear for passenger train speeds, is there an advantage to 2 more traction motors (there was some mention that a Genesis has only 30,000 lbs tractive effort at its minimum continuous speed related to its passenger-service gearing)?
Given that current levels of HP places on 4 axles are pushing weight limits, will be see 6-axle passenger units (again) so as to reduce axle load and hence track impact at speed?
For its next-gen power (i.e. the controversial Siemens locomotive), why isn't Amtrak and its state partners going with a lower HP unit, say around 2000 HP, in a much lighter unit? If the spec is a nominal 125 MPH, the British HST (Intercity 125) did just that -- they put a lighweight 2000 HP unit on each end of a push-pull corridor consist?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
My understanding was that the railroads using 6-axle passenger power did so specifically so their investment would be continued if converted to freight power. I specifically remember Amtrak's SDP-40F designed with that in mind, so some of their cost could be recouped "when" Amtrak died its natural death...
The F40C, like the U34CH, needs to put a great deal of power to the rail very quickly during acceleration, and spends much of its life doing so. Heavy commuter service, before high-performance wheelslip control. I see no further reason to wonder about that aspect of the design, either...
It's more complicated than that since most lines were still buying 4 axle freight power at that time. They didn't need passenger versions of 6 axle freight power to be able to use them in freight service later on. Something like a cowled GP40, which we essentially later got in the Dash 2 era, could've been put to useful freight service.
I suspect the Santa Fe for instance went with passenger versions of CC's because they had just bought a lot of modern EMD GP's and were focusing on 6 axle freight power at that time. I'm sure Santa Fe would've had no qualms at that time with a 4 axle cowl in freight service at the front of something like the Super C.
A lot of it was also affected by what was offered by the builders at the time. Neither EMD nor GE offered a steam generator option in any of their four-axle designs after about 1965. Alco offered that option in the C420 but not in any of their other four-axle models. At any rate, relatively few locomotives sold after 1965 were equipped with steam generators for passenger service.
CSSHEGEWISCH A lot of it was also affected by what was offered by the builders at the time. Neither EMD nor GE offered a steam generator option in any of their four-axle designs after about 1965. Alco offered that option in the C420 but not in any of their other four-axle models. At any rate, relatively few locomotives sold after 1965 were equipped with steam generators for passenger service.
The modern-day analog to this is the four-motored, six axle AC locomotive. Why not just build a four axle AC locmotive? You should! But trying to stuff all the necessary equipment plus desired fuel capacity into a four axle package and have it come out at a decent weight per axle, without getting into exotic, expensive designs ain't trivial!
Paul MilenkovicWhy did the pre-Amtrak railroads, Amtrak itself, and Metra itself initially go with 6-axle power
(and NJDOT's U34CHs)
Was it for potential freight use or because you couldn't package a steam generator and water tank?
I'll vote "both/and"!
I always heard that EL was very keen on trying to use the U34CHs in freight service on weekends, so they helped NJDOT spec out the locomotives. They fit in well with ELs U33Cs and U36Cs.
You COULD fit a steam genny and water tank on a four axle platform - the CNJ GP40Ps did this. But, you wound up with a locomotive that had very high axle loadings. In fact, when some of these came into Juniata for rebuilding (after NJT had done the HEP conversion themselves) , the were weighed and came in at over 300,000 lbs with full supplies.
oltmannd (and NJDOT's U34CHs) Was it for potential freight use or because you couldn't package a steam generator and water tank? I'll vote "both/and"!
Bet ya a case of Black Douglas you can't show me a U34CH with a steam generator...
Also bet you can't show me an EL SDP35 with a steam generator installed, either...
I recall that someone was upset that someone else was using locomotives 'over the weekend' and returning them with low fuel. Could that be NJDOT with the U34CHs?
I've read several stories of the Milwaukee "borrowing" locomotives in run through service without permission during layovers at Milwaukee yards. I suspect the Rock also did this when the opportunity presented itself with a reasonable chance to get away with it in its later years.
Most recently, there was a story a few years back in one of this publisher's magazines about an incident on the Milwaukee when the Erie Lackawanna discovered that a set of freight conversions of E8's were missing that had came in on a morning transfer run.
Usually, the departure of this power that was laying over happened late in the day. But apparently it was early that day so their absence was finally discovered when the EL crew couldn't locate their power.
Are these actually a B1-1B configuration, or an A-1-A, A-1A arrangement, like on the old E and PA units?
Doug
May your flanges always stay BETWEEN the rails
OvermodBet ya a case of Black Douglas you can't show me a U34CH with a steam generator...
Nary a one! Not EVERY six axle in passenger service was there for steam and water... The general case is allowed to have exceptions....I hope.
OvermodAlso bet you can't show me an EL SDP35 with a steam generator installed, either...
SDP45s were "P" for the huge fuel tank. Had to take those UPS trains all the way between NY and Chicago with out a fuel stop. The goofy fuel tanks on the EL SD45-2 were for this reason also.
The SD70ACe-P4s are B1-1Bs. While EMD is considering them SDs, GE is calling their A1A-A1A units ES44C4s, retaining the C. So, the distinction seems less about traction motors and more about axles than in previous years.
challenger3980 Just to confuse things EMD is currently offering a variant of it's SD70ACE unit with only 4 of the 6 axles powered, 2 are idler axles making a B1-1B wheel arrangement but the model will retain the "SD" designation.. Are these actually a B1-1B configuration, or an A-1-A, A-1A arrangement, like on the old E and PA units? Doug
The U34CHs had the HEP alternator equipment in the "steam generator room" behind the cab.
EL SDP45s might be best considered SD45As, as they were stretched similarly to the IC SD40As.
EL's SDP45's were true SDP45's.
They have the squared off long hood at the rear and the internal machinery arrangement was also shifted a bit forward to help balance the different weight distribution from the steam generating equipment. That's why they had ballast in the empty steam generator compartment despite it never being intended that they'd have a steam generator.
So I'm not if SD45A is a superior designation since they have all the traits and general specifications of a SDP45, just minus the passenger specific equipment. Even "SD40A", despite being neither a true SD40 or a SDP40 just minus the steam generating setup, wasn't an official designation. To EMD, they were still SD40's despite the longer SD45 frame and their hood and internal machinery arrangement are that of a standard SD40 rather than a SDP40.
EL's SDP45's are SDP45's with all the major modifications inherent with that variation, just not outfitted with the passenger specific equipment onboard. Would be like taking the PH out of F40PH just because it's on a regional, regeared for freight, and the HEP equipment has been deactivated and removed.
Squared off long hood on the EL SDP45? Say what?
Also to note, EMD called the second order AC130s.
ML
GDRMCo Squared off long hood on the EL SDP45? Say what?
By Jove, on reflection, I think the man's right! See this example:
which shows both ends of this series of SDP45 together.
Yes, other railroads had flat ends for the steam-generator compartment. The difference might be that they actually intended to put steam generators in them -- EL never did; they bought the longer model for the bigger tankage...
The flat ends were on the SDP-40s. Barely enough room for a fat guy to get around the rear of the unit. I think MRL had one of the last ones.
Randy
MRL has one still in service, upgraded to SD40-2 specifications. KCS has some (I think similarly upgraded, ex TFM and NDEM), some of which were rebuilt to SD22ECOs. Some are scrapped, and a couple may be leasers.
Randy Stahl The flat ends were on the SDP-40s.
The flat ends were on the SDP-40s.
What I meant is they had the bodywork, minus a few openings, that a standard SDP45 did. It isn't like Illinois Central's SD40A's that were stock SD40's above the frame.
SDP40's and steam-generator equipped SDP45's (GN and SP) had the flat ends. To add to the confusion, L&N had some SDP35's built without steam generators that also had the flat end.
The ONLY SDP-45 I've ever seen and worked around was the WC6634 (ex EL) and it looked like someone glued a GP 40 hood on the carbody right behind the radiator flares. (as pictured above) . These certainly did not have a flat end like the SDP40 that MRL was running at the time. The EL SDP- 45s had enough room to walk around the rear hood.. the SDP40s were tight and the one I remember had a ladder on the rear instead of a step well.
I never saw an SDP35 but the entire 35 series were my least favorite locomotives because they were electrical maintenance and wiring nightmares.
Not too surprising when you consider that the 35 series was pushing the limit for a DC main generator.
I became very familiar with the bottom of GP and SD 35 generator pits repairing flashed over brush holders and copper balls between commutator bars. Not a 35 series fan for sure.
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