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[quote]QUOTE: Originally posted by jgfuller Very interesting insights from one who has built the locos! ACs have worked very well in heavy haul service -- the problems so far seem more with the diesel rather than the transmission. 6k HP is a lot in a mobile environment. So far as I know, UP doesn't use their 70s much in coal service. And the tractive effort advantages of ACs in general service may be offset by higher first cost. As many of those posting have noted, it's the reliability of the 40 that is important. The 70 does all that, in a newer package. I'd predict that in time the 70 will supplant the 40 as an icon of consistency. How have lower HP ACs fared, compared with the high HP models? Hooking up a 710 engine with an AC transmission and radial trucks sounds good -- I guess this would be an SD80MAC (or 70MAC), eh? UP shows having 300 SD9043ACs, with 4300 HP, but no other EMD ACs besides 62 6k HP models. And about 1000 GE 4k ACs, compared with 60 6k units. So this HP seems to work OK with either transmission. One had to wonder when EMD had to go to a 4-cycle design to get 6k HP -- good grief, an EMD that sounds like a GE!! [/quote] The 4000-to-4400 HP AC's have been much more reliable but not quite as good as the DC fleets. So AC has been great for the railroads bottom line, three units replacing five DC's for unit trains, etc. Yes, especially in the coal business where higher HP (or top speed) is not needed. They may not run like DC's or the good old SD40-2's but most often the trains make it to their destination even if one of three units has failed. ...and those missing two units (#4 & 5) didn't burn all that fuel! If it wasn't obvious, fuel is the rr's #1 operating expense. The other point is that the AC's can struggle along at ridiculously low speed and still get home, when a DC consist would have stalled. You cannot burn up an AC motor and there are no "short time" ratings like the DC's. What crossed the line was 2-for-1 replacement and/or single unit consists, with a less reliable 6000 HP unit. That creates more "dead-on-the-road" type failures. I haven't been around since they've been in prime-time but all you have to know are the MTBF (mean time between failure) numbers to know its been painful. Again the theory was great, save over half the fuel costs every trip. That would pay for those 2-point-whatever million dollar locos in no time. [:I]However, the 6k HP units needed to run 25-40% BETTER than their lower HP brothers to avoid trains being broken down on the mainline. Any reasonable person knows that is a long shot given the additional variables of new engines and all the new systems that go with them. Again, I'm not around anymore to know where that line is so I don't know how close they are. I fear its not close enough. BTW, the fabricated crankcase of the 2-cycle engine was at its limit and would have been way too expensive to make for that HP, so that as well as fuel efficiency and emissions lead to the cast crankcase, 4-cycle H engine. (I am not saying the 710 has emissions issues) It doesn't really sound like a GE but it is a long way from my favorite 20 cylinder 710's on the 80MAC's. Find those things and video as much as possible...[:)]
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