Blow off Valve
 

would anyone know if a BOV (Blow Off Valve) would sound nice in a mini cooper
and if they are universal?
and how much price wise?!

Most are using THe HKS super sequential or the Forge BOV's ... But are getting more turbo log as they are expelling the boost ...I believe the HKSSS is non adjustable..at least for the new models. The reason for the turbo lag, engine hesitation, stuttering, any of those symptoms is due to venting metered air that the car is expecting back into the intake tract. My suggestion is research on the recirculation kit for the HKS bov's to send that air back into the intake tract as per stock specs so the maf doen't go nuts. You will still get quicker response after a shift + nice sound as well.

bov on mini
 

if i get the Blow Off Valve (BOV) do i just need the BOV or do i need parts with it also?
please let me know
thanks

As mentioned I'd get the recirc kit ...