Efficiency and utiliziation of space first. Smaller engines usually have worse efficiency than larger ones.* Two smaller engines will take up more space than one larger and the support systems (fuel, exhaust, cooling and controls) has to be duplicated for both, decreasing available space, reliabilty while driving up complexity and maintenance requirements.xthetenth wrote:What are the problems with being powered by twin engines, and how pronounced are they? Is it a matter of reliability, efficiency (size/fuel) or all of the above? I can definitely see an appeal for running two engines in redundancy and not having to use the biggest engines available. I'd see even more in the layout if you used two of the standard medium tank powerplant, like the Tiger (P) did. This is a purely theoretical question to me, since the Tiger's first combat deployment came about nine months before that of the Ferdiand, and although both were pretty disastrous, I don't remember the Tiger doing nearly as poorly by the time of Kursk as it had against the Sinyavino Offensive.
Now the biggest problem is what to drive. If both engines drive the same crankshaft, either they had to be kept completely in sync or additional equipment which balances between the two has to be installed. Keeping them in sync is not doable until modern computer controls became availabe somewhere in the 70s-80s and the mechanical equilazer is something that had to be accomodated, adding more complexity while decreasing reliability. If you plan to run them separately, then you have to duplicate the things they drive too, for example generators, but don't try to use them to power the left and right tracks separately. In case of generators, if they output AC, they had to be kept in sync too but solving that is easier than the mechanical issues.
* Unsurprisingly the most efficient internal combustion engies are the house sized ones powering supertankers and similar ships.