Smooth mandrel bent tubing -Polished -for use with factory 0-ring and intercooler piping -1/8" NPT threaded bung on rear for nitrous or a boost gauge fitting -The stock elbow has a sharp 90 degree lower inside angle, and a rough sectioned upper , which both restrict airflow.
The orange lines in the picture above show what the stock elbow looks like inside. The picture below shows what is happening to the airflow inside the elbow. (Flow analysis was set up on both intake elbows with the exact same parameters.) Because of the sharp 90 degree turn on the stock elbow, note how all the airflow is bunched up at the rear. This means that approx 30% of the available inlet area (front portion) to the engine is useless. The average overall pressure drop difference (at the base of the elbow) between the stock and new elbow is approx 2 psi. This means that in order to achieve the same amount of boost at the engine, the turbocharger (and engine) have to work harder to overcome that pressure drop. With the stock elbow, this results in higher Exhaust Gas Temperatures, lower fuel economy, and more stress on the turbocharger.
Since the new elbow (below) has the smoothest possible transition through the whole elbow, the entire area at the bottom of the elbow is used.