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[quote user="YoHo1975"]  What are the limitations on Diesel electrics that they can't develop HP at higher speeds per hp?[/quote]I assume your question is based on the flattening off of a diesel locomotive's horsepower curve as it accelerates, whereas a steam locomotive's horsepower curve continues to rise as it accelerates.  There are two ways to look at this flattening off characteristic of the diesel. One way concludes the characteristic to be a disadvantage, and the other way concludes it to not be a disadvantage.  It appears to be a disadvantage because a train needs increasing horsepower in order to increase its speed, and the diesel reaches its maximum horsepower early and cannot continue increasing it as the train accelerates.  However, it is not a disadvantage when you consider that the diesel is simply able to deliver all of its horsepower early in its acceleration.  Some might call this a peak in horsepower and say that the diesel's HP peaks early where it is not needed.  In this context, the term peak suggests a high point with an immediate fall-off.  Yet that is not the case with the diesel.  It continues to develop its maximum horsepower all the way to top speed.    Not only is this ability to reach maximum horsepower early not a disadvantage, in some cases it is actually an advantage; for instance, when pulling a drag freight that requires the locomotive's maximum horsepower, but is so heavy that its balance speed will be say 30 mph. A diesel can deliver all of its potential horsepower at that speed whereas a steam locomotive cannot.  In MichaelSol's horsepower and tractive effort comparison tables posted in the other thread, besides the obvious flattening off of the diesel's HP and TE curves, there is the continuing increase of the HP/TE curves of the steamer, which seems to further reinforce the idea of a disadvantage with the diesel.  However, in order for the steamer to continuing to develop increasing horsepower to levels greater than the diesel's maxed out horsepower, the steamer must simply be a higher horsepower machine.  What would the comparison look like if you compared a 5,600 HP diesel to a 5,600 HP steamer, assuming that they both were capable of delivering their full HP to the rail?  The diesel will develop and deliver its full horsepower once it reaches 15 MPH while the steamer will not be able to deliver the same HP until it reaches perhaps 55 MPH.  I make this assumption extrapolating from MichaelSol's table (shown below) comparing the horsepower developed by a steam locomotive to that of a diesel, where the steamer delivers its maximum HP at 55 MPH.I believe the correct way of looking at this is that it is not a failure of the diesel to keep up with the steamer in developing more and more horsepower, but rather a failure of the steamer to develop its full horsepower until it reaches a relatively high speed. <table border="0" cellspacing="0" cellpadding="0"><tbody><tr><td>MPH      </td><td>Diesel-electric         </td><td>Steam </td><td>      HP  needed</td></tr><tr><td>5</td><td>    4,278</td><td>1,806</td><td>         307</td></tr><tr><td>10</td><td>    5,133</td><td>3,613</td><td>         743</td></tr><tr><td>15</td><td>    5,600</td><td>4,516</td><td>      1,239</td></tr><tr><td>20</td><td>    5,600</td><td>5,600</td><td>      1,839</td></tr><tr><td>25</td><td>    5,600</td><td>6,323</td><td>      2,562</td></tr><tr><td>30</td><td>    5,600</td><td>7,226</td><td>      3,426</td></tr><tr><td>35</td><td>    5,600</td><td>7,677</td><td>      4,446</td></tr><tr><td>40</td><td>    5,600</td><td>7,948</td><td>      5,641</td></tr><tr><td>45</td><td>    5,600</td><td>8,129</td><td>      7,028</td></tr><tr><td>50</td><td>    5,600</td><td>8,310</td><td>      8,624</td></tr><tr><td>55</td><td>    5,600</td><td>8,400</td><td>     10,447</td></tr><tr><td>60</td><td>    5,600</td><td>8,310</td><td>     12,513</td></tr><tr><td>65</td><td>    5,600</td><td>8,219</td><td>     14,840</td></tr><tr><td>70</td><td>    5,600</td><td>8,129</td><td>     17,445</td></tr></tbody></table>
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