The BRG SV650 tank risers raise the gas tank up approximately 3/4" so the carburetors and/or fuel injection system can get more air. The way the factory has the airbox in tank configured, there is a fair bit of restriction and there is a pretty good horse power gain to justify raising the tank as you can see by the Dyno around with little bitty jetting tank space usually get a significant difference in horsepower. Will Fox, last year's top racer in the AFM 650 Twins class very much enjoyed the benefit of it.