Q is the first revision of the original TiAL BOV. The Q bolts up to any standard TiAL flange, no re-welding.  This is the highest flowing BOV on the market.  It's offered with a variety of springs for different vacuum levels and a special spring specifically for supercharged vehicles

QR is the more compact recirculating BOV. Optional 1.0" (Subaru) 1.29" (GTR) or 1.34" (DSM/EVO) reciruclation port, uses the standard TiAL V-band flange and can be converted into a standard Q BOV by swapping the bottom piece.