This isn't accurate. The 92-93 manifolds are significantly larger at the outlet than any other years, and as far as I know there were no changes to the manifolds after that (other than maybe the air injection ports).
this is the information I've heard as well. It's easy to see though how they would flow great. Look at how they're designed. They neck down to a venturi like a carburetor. that low pressure area right before the flange will be great for scavenging.
