In regards to the stock CVH rs turbo manifold i've always heard or read on here that they are good for 300bhp?

But why don't people change or develop a new manifold to run for example like a twin scross turbo does... Where 1-4 and 2-3 (equal length) cylinders are connected with two exit holes for the exhaust gas to aid in scavenging and a quicker spool up time. Think i noticed in one of you guys pics. But would the exhaust housing of a T3 also need changing to suit?

Surely the standard manifold can always be improved even at lower levels of tuning say 200bhp?