[CBFryman]

with twin charing im assumeing you mean a supercharger feeding into a tubro feeding into the engine. It isnt so much that it spools faster, its that the supercharger takes care of boost untill the turbo spools, the drag of the supercharger is then removed and the turbo takes over boost completely.

Good in theory but im not sure it is worth the headaches.

The other thing you may be talking about is sequincal turbocharging, such as on the RX-7 TT.

This is where a smaller, faster spooling, turbo feeds into a larger turbo untill the larger turbo spools and the nthe waste gate for the 1st turbo is opened almost completely so that the 2nd, larger, turbo is taking care of all of the flow.

This works great but has its HP limitations due to the fact thatthe 1st turbo is in the way of the 2nd turbo. This is why RX-7 Enthusiasts recocmend doing a true twin set up or a single large set up on the 13BTT once you pass around the 400hp mark.