R33 you are right, but when installing significintlly larger turbo's for a twin setup you also must replace the exaust manifold and new intake manifolds must be created because of the larger intake diameter.. even the old AFM's will be useless...
2 Large turbo's will never fit in the factory position, they have to be moved up.. hence a new exaust manifold, also with external wastegate fitted.
The single system becomes a hell of alot cheaper when you are going for HP upwards of 800HP. I think from what I have heard as much as 30% cheaper than a twin setup.. but even for 500 + HP a single system can prove cheaper.
As for performance difference, both systems seem to have reached max boost of around 1.3bar at almost identical RPM. Trust T8834D and Twin TD06. The twin setup may have a slight better responce..
So ofcourse if you keep the twin system with the stock manifolds the twin will be cheaper.. but when you are paying $4000 for a turbo.. and still have to buy the manifolds.. I think I would be buying one big one
