Originally Posted by richy
Its an 05 bone stock. I actually pulled down a garage with it the other month. I was half throttle not going anywhere. I let off real fast and it made the sound exactly like a blow off valve would. My sister used to have a pimped out ricer that made the same exact sound when she let off. Mine does it all the time but that time was particularly loud.
that sound you heard is nothing like a blow off valve sounds. What you're hearing is compressor surge. It happens when you have pressurized air being pulled in via the turbo under boost, when you abruptly let off the throttle there is excess boost pressure that has no where to go, so it hits the wheel on the turbo which causes it to spin in reverse while air is being pulled and pushed in at the same time.
if your sister's ricer made that sound then her blow off valve was not working correctly and she was causing damage to her turbo.
The VGT acts as both a wastegate and a B.O.V. as it is able to adjust itself to allow airflow. Sometimes however it will not act quick enough and you will hear the compressor surge, or "turbo fart" that is commonly used among powerstroke owners.