they share the same manifold in mose cases besides a v6/v8. in a i4 or i6 you split the manifold in half which in a lot cases is not the best bang for the buck. i could be wrong but the smaller turbo will spool faster causing more exhaust sooner so that the larger turbo will spool faster. as far as the charge pipe goes, they end up becoming one rather its before the intercooler or at it. (ex.) 2 charge pipes go into the intercooler on the hot side and one pipe comes out of the cold side.