they do nothing , but waste your money and make your wallet lighter go to powerbrokerz.com and they will tell you why they are a waste of money.. oh and sometimes they make air leaks
On a shee they help because they stabilize the air going into the twin cylinders, but a blaster has no use for one since its a single cylinder and has no need for equal pressure in two cylinders ( if that makes any sense ). It would be like putting a duel pipe on a single cylinder, it would look cool, but do nothing for performance.
On blasters, don't they help with low end lag if you have oversized carbs? That's what i thought, not a whole lot of noticeable gains, but enough to keep your bottom end from sucking. That's what i was under the impression of