Used TurboXS RFL blow-off valve in working condition. No adapter plate included. This blow-off valve is REALLY loud, probably one of the loudest on the market.

They seem to be going for about $130 new so I figure $50 shipped for a used one is a fair price.

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)