open vs unsilenced air cleaner

Depends — some "unsilenced" air cleaners can be pretty restrictive. For example, on slant sixes, some of the 10" baseplates leave something like a 1/8" gap all the way around — that's not much area for air intake. On the other hand, most V8s have a much larger gap that is effectively the same as an open element. Consider — larger diameter means more intake area. So the big 20" diameter unsilenced can feeding a 15" diameter filter element is effectively identical to an open 15" element, because the intake area of the air cleaner is so much larger than that of the element that it might as well be infinite.