| Long answer:
Like sps955 says, the rubber restrictor annulus on the superbike inlet runners are designed to reduce air induction noise to meet US EPA (and Euro?) limits. These are not inlet restrictors designed to limit performance like those used recently on some Japanese bikes to meet maximum speed limits. The superbike blocks merely increase the velocity of the air as it passes through the device but reflect sound waves back to the engine inlet. Said another way, the pressure drop across them is very low as opposed to a high pressure drop created by a dirty air filter. Removing them increases the free air volume between the velocity stacks and the stock air filters which has the added benefit of a better throttle response (but no more power).
Short Answer:
Like weeksy says, if you take out the restrictor blocks you’ll get a nice intake growl. |