You're an engineer and you aren't "grasping" one of the fundamentals of fluid dynamics?

Any restriction on the turbo inlet produces a partial vacuum. The turbo can easily compensate for this, by increasing the pressure ratio and RPM. This can only be done by increasing the work done by the exhaust, which increases exhaust backpressure and increases engine pumping losses.

Just because you don't see black smoke doesn't mean your engine is running at maximum efficiency.