The supercharger is on a clutch that would disengage after the turbo spools. The supercharger also has a wastegate that dumps into the tubo inlet and a bypass around it.
There should be very little parasitic drag with that setup. Unfortunately the Turbo/SC combo makes for a very complicated and heavy addition to any engine. It would also need the right EFI and electronic controls to make all the events work together optimally.
Very interesting project. I have thought of doing it myself if it could be justified.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8