Just found this on google search dude
Dont know if youve read it or anything

A twincharging system combines a supercharger and turbocharger in a complementary arrangement, with the intent of one component's advantage compensating for the other component's disadvantage. There are two common types of twincharger systems: series and parallel.

Series

The series arrangement, the more common arrangement of twinchargers, is set up such that one compressor's (turbo or supercharger) output feeds the inlet of another. A sequentially-organized Roots type supercharger is connected to a medium- to large-sized turbocharger. The supercharger provides near-instant manifold pressure (eliminating turbo lag, which would otherwise result when the turbocharger is not up to its operating speed). Once the turbocharger has reached operating speed, the supercharger can either continue contributing pressurized air to the turbocharger inlet (yielding elevated intake pressures), or it can be bypassed and mechanically decoupled from the drivetrain via an electromagnetic clutch and bypass valve or one-way valve (increasing efficiency of the induction system).

Other series configurations exist where no bypass system is employed and both compressors are in continuous duty. As a result, compounded boost is always produced as the pressure ratios of the two compressors are multiplied, not added. In other words, if a supercharger which produced 10*psi (0.7*bar) (pressure ratio = 1.7) alone blew into a turbocharger which also produced 10psi alone, the resultant manifold pressure would be 27*psi (1.9*bar) (PR=2.8) rather than 20*psi (1.4*bar) (PR=2.3). This form of series twincharging allows for the production of boost pressures that would otherwise be unachievable with other compressor arrangements.

However, the efficiencies of the turbo and supercharger are also multiplied, and since the efficiency of the supercharger is often much lower than that of large turbochargers, this can lead to extremely high manifold temperatures unless very powerful charge cooling is employed. For example, if a Roots blower with an efficiency of 60% blew into a turbocharger with an efficiency of 70%, the overall compression efficiency would be only 42% -- at 2.8 pressure ratio as shown above and 20 °C (68*°F) ambient temperature, this would mean air exiting the turbocharger would be 263 °C (505*°F), which is enough to melt most rubber couplers and nearly enough to melt expensive silicone couplers. A large turbocharger producing 27*psi (1.9*bar) by itself, with an adiabatic efficiency around 70%, would only produce 166 °C (331*°F). Additionally, the energy cost to drive a supercharger is usually several horsepower, thus if it can either be disconnected electrically (using an electromagnetic clutch such as those used on the VW 1.4TSI or Toyota's 4A-GZE) or allowed to freewheel and vent to the atmosphere, several horsepower can be gained independent of the efficiency gain by switching to one compressor.

Thus, switching the supercharger off at a certain boost or RPM threshold is most desirable, since a large, inexpensive journal bearing turbocharger can be used which will provide more than enough pressure and flow at high RPM for most twincharged motors. However, a smooth switchover can be very difficult to accomplish for non-OEM twincharging applications.

Parallel

Parallel arrangements typically always require the use of a bypass or diverter valve to allow one or both compressors to feed the engine. If no valve were employed and both compressors were merely routed directly to the intake manifold, the supercharger would blow backwards through the turbocharger compressor rather than pressurize the intake manifold, as that would be the path of least resistance. Thus a diverter valve must be employed to vent turbocharger air until it has reached the pressure in the intake manifold. Complex or expensive electronic controls are usually necessary to ensure smooth power delivery.