German Engine development

[Ifor]

Forgive my lack of knowledge but I've been wondering for quite awhile about axis vehicle and aircraft engine R & D. Can anyone point me in the right direction for books, articles, etc covering this issue? Was the R & D set back by:-
a,Hitlers opinion that the weapons he had early in the war were adequate(is it true)?
b. A shortage of the right materials (I should think this is a given as the war progressed and access diminished)?
c, Lack of technical ability(I can't see this as reason unless they took the wrong options)?
d, another reason?
I think I read on one the topics that supercharger development was behind the allies.
Again forgive my ignorance. I ave searched on the site but couldn't find anything.
Ifor