Can anyone speculate (or perhaps know) why the DDA40X “645” 3,300 HP prime mover was not used in the SD/GP40’s (we all know that a “645” 3,000 prime mover was and has always been used for those locomotives)? Also, was the 3,300 HP engine ever used in anything other than the DDA40X?
Just researched your question. The only other locomotive to use the 16-645E3A prime mover was the RENFE class 333 locomotives.
The SD/GP50’s used the final tweak to the 645 with 3,500HP to the traction alternator. Reliability wasn’t that great as the extra power required 950rpm from the 645 in run 8.
Thanx for the info. Any idea (if the 3,300HP engine ran well in the DDA40x) why EMD might have tweaked it to 3,500 (ie…not just left it at 3,300HP)?
Thanx. So EMD never used it in anything but the DDA40X?
So, no one knows or can guess why the 3,300 HP “645” was not used in the SD/GP40’s? Why put a 3,000HP engine in when you have a 3,300 HP engine? That’s my real question, just phrased another way. I thought someone out there might have read something somewhere or heard something abot why.
As implied in other posts, the extra horsepower comes at a cost in the strain on various engine components. Earlier, EMD hit a similar maximum at 2500 HP in the 567 engine, and the 645 was developed to address that issue.
Since I’m unaware of significant engine issues with the Centennial’s higher rating, one possibility is they thought it would be too slippery on a Geep. There’s significantly more weight on each axle than your average GP40/GP40-2.
Doesn’t explain though why it wasn’t tried as a lower cost alternative to the SD45 and SD45-2. In particular, the extra 300 hp seems like it would’ve been a good fit for Union Pacific’s high speed SD40-2’s that were intended for high speed service alongside the Centennials.
I think the 645E3A as put in the SD45X had very similar ‘horsepower density’ to the 3300hp version on a per-cylinder basis. If there were an engine-related problem other than one associated with longer crank, greater torsional stress, etc. the history of those locomotives might serve as a guide.
Thanx to all who replied.
LEO: "Doesn’t explain though why it wasn’t tried as a lower cost alternative to the SD45 and SD45-2.:–exactly my point. Unless I hear further I’m going to presume no one has any idea. It just didn’t make sense to me.
I think the real question is why UP and/or EMD wanted 6600 HP from the DD40AX and not 6000.
The “X” in the model usually indicated “experimental” and these were generally used to “try out” new things. I’d hazard a guess EMD want to see if they could push another 10% from a 16-645E3 engine and UP agreed to go along for the ride.
Why didn’t other roads want the extra 10% HP? Most likely because it didn’t come with another 10% of tractive effort at minimum continuous speed.
The 3500/3600 HP SD50s had a large dose of extra tractive effort available at MCS due do upgraded traction motor windings and Super Series wheelslip control.
It would also put the SD40 too close in the catalog to the SD45. Why have two products competing against each other. Also, that would have put a huge gap between the 38 and 40 series. Notice that neither the U33C or U36C sold that well. If they had dropped one of the models, the production would have been better.
The U33C and U36C weren’t really different locomotives. GE just evolved their 6 axle product. The U36C replaced the U33C in the catalog. If you wanted lower HP from your U36C, it was pretty simple to arrange. GE used a constant HP excitation scheme - it was just a blue-faced card change.
The SD45 was pretty much a dead model when the DD40AXs came around. ATSF, EL and Clinchfield took a few SD45-2s - and they were pretty decent - but the SD40 pretty much ruled the roost. It had the right mix of HP and TE. It could handle the same tonnage as an SD45, just a bit slower over the road (with less fuel), did not need field shunting, and the early problems with the 20-645E3 engine left a bad taste in CMOs mouthes.
U33C- 1968-75
U36C- 1971-75
I humbly suggest that the answer to most of these questions could be found reasonably directly in UP’s own motive-power preference in this period, more specifically with respect to the inherently high-speed operation the Centennials had updated horsepower for.
UP did not buy or update 20-cylinder locomotives to run with the Centennials. What they did use was SD40s, regeared for higher speed but NOT upgraded to 3300hp with E3A mods although all the usual parts and maintenance arguments for engine commonalty would point toward doing that, and the additional horsepower would seem as fully usable at high speed with 12 TMs per 6600hp as with the 8 of a Centennial.
OK, I understand the strain issue. But if it ran in the DDA40X why not run it in the SD40-2?
“I think the real question is why UP and/or EMD wanted 6600 HP from the DD40AX and not 6000.”—Great question and “…guessing EMD wanted to see if they could push another 10% from a 16-645E3 engine and UP agreed to go along for the ride.”… is an extremely valid supposition. Thanks. That’s changed the whole perspective of my original question.
“Why have two products competing against each other.”—One answer would be: If given a choice of 3,600 HP w/20 cylinders vs. 3,300 HP w/16 cylinders I would choose the latter just based on economics.
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