S-MAX's BOW300 is not just a blow off valve, it is a musical instrument.  It has one of the most unique customizations features on the market.  With a simple adjustment (no tool required) you can change the blow off sound of your turbocharged engine; from an ear piercing whistle to a more subdued whoosh.  The BOW300 has small parts to change the resonance of the blow off air depending on their alignment.

 

  Comes pre-installed with 5-12 psi spring.  Also includes a 7 to 20 psi spring and an adapter to combine both spring rates of 10 psi to 32 psi.