a mate of mine had a surbo and he said the only way to tell it was there and to "feel" anything was to momentarily back off at about 3k and it would create the vortex effect and it DID work. However, it was bloody hard to make it do it and the gain was lost in the backing off, so back it went!
Dont bother, buy a good induction kit instead, even a poppy coral is better! (and thats saying something)