Agreed Beepbeep. Too many people think you actually gain power with BOV's.
Though, there are definitely improvements that you can make by using them. In my experience, the stock 951/965 type Bosch plastic bypass valve is relatively weak and easily wears out. I've had the problem multiple times on multiple cars where they get worn out and don't remain 100% closed in off boost conditions. Because of that, then you see increased spool time initially as well as between gears. There are aftermarket units like Forge BV's that are just made of better quality materials and function better, so there are improvements to be made. Not to mention, there are some BOV's like the HKS super sequential which have a pull type valve. I personally love those a lot as it's physically impossible for them to leak, so basically you'll never have a problem and you can still recirculate if you so desire. Anyways, the only thing BV's/BOV's will ever do is eliminate lost power and lost response, though they certainly don't "add" power.
'87 3.2 Carrera - 3.4l, Billet Design equal length headers & full bay IC, 60-1 T4 .81a/r, Kinesis Supercup replicas, Big Reds at all 4, 964 body conversion, 964 Turbo S rear spoiler