Prime Mover RPM. The SD75s have an RPM higher than that of the SD70s.
The model was a response to GE's upping their horsepower ratings when they changed from the -8 to -9 series.
NorthWest The SD75s have an RPM higher than that of the SD70s.
The SD75s have an RPM higher than that of the SD70s.
Ah, that explains why they had SD50-esque teething troubles when they first came out. CN's mechanical dept worked long and hard and eventually came up with about 20 different fixes that finally made them reliable. I have no idea what specifically was done, but they retain their 4300 hp rating and currently are CN's most reliable power according to local management (longest mean time between failiures), albeit with regular dynamic brake problems. Guess there's something to be said for a simpler computer and giving the engineer more manual control of everything (wheelslip, etc).
OTOH, BNSF seemed to give up on theirs, never reliable, only the recent locomotive shortage has seen them recalled from the leaser's dead line. I was quite surprised that CN didn't pick them up, given our management's love of cheap secondhand power.
Greetings from Alberta
-an Articulate Malcontent
The SD75Ms are now back in service again since I saw a former ATSF silverbonnet SD75M on a BNSF consist over a week ago. From what I've heard, the SD75Ms are being renumbered into the #200-series to make room for more ES44C4s.
The 200 series were their original numbers, IIRC. So they are being numbered back!
doug uHow much more rpm , 50 or 100 . The new sd70ace hp rating is about 4300 hp did they keep the higher rpm to obtain this power? They still use the same 710 powerplant don't they. The GE power increase is even more difficult to understand then EMD , at least when increase the bore or the stroke there is a power increase. GE has not change the bore and stroke on their engine , as far as I know. I don't what has happen to the RPM also but I think it went up over time. There less information about GE engines in magazines like "Trains" I see more about EMD.
Don Oltmann and P Cook are two people I'd like to see comment on this.
My understanding was that much of the increase was due to better injection control than increasing governed speed -- you can get higher effective cylinder pressure over a longer portion of the stroke by modulating the injection of the fuel charge -- like a fancier version of pilot injection.
It's also possible (with 'sophisticated' enough injection control) to rotate higher power among groups of individual cylinders, comparable in principle to how GM did 'limp-home' on the Northstar engines. This works better on engines like the QSK with individual turbos for groups of cylinders -- you temporarily increase power for a set of cylinders (with comparable boost from its turbo) for a certain number of rotations, then switch to a different set, etc. This gives a higher thermal cycling, but 3 times the cooldown time for a given cooling-system 'reservoir' capacity.
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