The idea behind turbos is to harness the free wasted energy coming out your exhaust pipe. You are correct in the fact that turbos do create back pressure and in an ideal world the back pressure in the manifold will match intake manifold pressure. For example if you have 6psi of boost then you should see 6psi of exhaust back pressure in the manifolds. There are TONS of configurations that contribute to spool up time and back pressure and both are inter-related. Turbine wheels are a large contributer as is the A/R (diameter of the turbine housing) and of course manifold design. I specifically chose a turbo with an integrated wastegate, because it wastegates all 4 cylinders, does not divert the exhaust flow path, in the manifold, away from the turbo, and there is no "dead space" from a long tube coming from the manifold to a location where a wastegate can be placed. Assuming you have the space and a properly sized wastegate valve, then internal wastegating is the way to go. Another way to reduce back pressure is to build what is called an "anti reversion" manifold. These manifold have a collector and/or primary tube that contains a one way check valve if you will. This check valve stops the pressure wave of the other cylinder's fire from going up the manifold tubes and back into the head ports. I have one of these manifolds on my SRT4 and as a result I spool that big ole T-72 by 4k RPMs.
