Hi Eddie,
Nice project. As far as intake ducts go for our models the more volume you have in front of the engine the better. General rule is that any duct that expands in volume should not have a sidewall slope of more than 7 degrees to prevent seperation of the airflow. This means that the air in front of the turbine is moving slower than at the intake and thus has more pressure, helping the compressor a bit and countering the negative pressure effect of the exhaust venturi effect in our bypass sytems from reducing the pressure the inlet sees. Narrow inlet duct + lots of bypass = easy flameout of the engine.
Cheers,
Andre