There are several reasons why Straight eights have gone and are being replaced by V engines. First the occupied space is important, even if you add two motorcylcle engines together it will still be a long engine. A second disavantage is that it becomes impossible to put a straight eight in a transverse position, it will simply become woo wide. (The Miura V12 was the best they could ). That rules out any option to use it for a FWD car if so desired.
A third issue might be of more technical nature, and relates to the length of the crankshaft. The larger the number of inline cylinders, the longer the shaft has to become, and the more difficult it becomes to reduces vibration, certainly at the high revs modern engines are now achieving.
I'm not familiar with the 7 cylinder torpedo engine that you mention, but in marine diesel propulsion you can get almost any configuration you want, just by putting together more cylinders. 7 cylinders engines are rather common, also 9,10,11,12,13 and even 14 cylinder versions have been produced. In terms of vibrations the single crankshaft poses the same problem as described above, but these engines barely go over 100 revs (a minute ), while producing over 100,000 BHP.
And welcome to UCP, hope you are going to like it here.
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