The split plenums are usually to optimize flow for lower rpm ranges, while the open plenums are usually for higher rpm ranges. There are many manifolds of both designs whose operating range overlap each other, depending on the design.
Thanks, that's what I was thinking but I wasn't sure. I think the split plenum is used to get a smaller plenum volume to allow more flow velocity at lower rates as compared to a big open plenum being able to flow more voume at higher rates.
My 460 came with a Weiand split plenum high rise manifold. That should make it a bit better for the street than an open plenum design.
I don't know what cam is in it and it has stock heads. I'm guessing the heads aren't ported because it was built using stock exhaust manifolds. It does have a nice dual exhaust.