| The rubber restrictor annulus on the superbike inlet runners are designed to reduce air induction noise to meet Environmental Protection Agency legal 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. If you take out the restrictor blocks you’ll get a nice intake growl, but not much else. |