Summary
The video below gives the sound of the Shuenk IS48 “ported shroud” version of this turbocharger.
Setup:
The recording setup consisted of a GoPro Hero 13 placed next to the ECU, behind the driver’s side headlight, held in place with some foam.
The GTI is using the Eventuri closed intake and a stock diverter valve (DV).
Note: Placing the microphone in the engine compartment emphasizes the sound from the turbocharger, but it is louder than what is heard in the passenger compartment.
The “ported shroud” concept adds a pathway for air to enter or exit the compressor near the exducer.
The goals for the ported shroud include addressing surge conditions. Higher-pressure air from downstream of the turbocharger reaches the exducer, potentially causing the airflow across the compressor blades to stall. By having the opening near the exducer, the higher-pressure air can be bled off into the intake air, reducing the risk of compressor surging.
At very high airflows, if the flow path to the compressor inducer becomes choked, the additional opening can draw in more air at the exducer, potentially allowing the turbocharger to flow more air than it would with a conventional housing.
Of course, there’s no free lunch, and the opening can lead to a drop in the compressors’ efficiency in some of the operating range.
The added pathways for air to flow produce a louder sound than a conventional compressor housing, as the video illustrates.