Sorry to pick at the info, the magnapack is a strait through muffler with large perforated stainless steel core.
They use a stainless steel mesh for sound control. A muffler with chambers like a Gibson or a Magna flow XL would be better for low end torque.
The engine needs something to reflect the pulse wave back at it to be able to tune its self. But once you have changed the dynamics of the exhaust system or have stepped up to a S/C or turbo the pulse of the engine changes and u no longer worry about the engine seeing the muffler.
There is a article in SuperChevy magazine about mufflers and how they react to the engine.