Straight eight engines have slowly vanished from the automotive scene in the 50s. Now I understand that with the then current material technology and bigger displacement engines the demands made on a relatively long crankshaft and the overall length of the engine made designers switch to a V configuration. As I am not an engineer (and had no luck in searching on the net for clues), I'd like to know whether there are other reasons for not choosing such a configuration. Specifically, what I'd find very intertesting would be a straight eight made as a combination of two motorcycle 4 cylinder engines, which are reasonably small in displacement and short lengthwise, meaning that the mentioned two problems could be overcome.

Additionally, I came across 7 cylinder engines being used to propell underwater torpedoes (Saab Underwater T2000). They do not seem to be radial (from my understanding) and use something called axial valves. Anyone know more about it?

Additionally, I am interested in some decent literature on the subject. Browsing through Amazon does yield results, but most books are in the 200 US$ plus bracket, and that is used. Any suggestions welcome