S&S 124 CI and 145 CI fuel injected engines feature dual bore throttle bodies/fuel rails. Dual bore involves individual intake tracts for each cylinder. To achieve maximum performance those dual bore throttle bodies/fuel rails are designed. Dual Bore Tuned Induction systems have independent tuned length intake runners. By utilizing air column inertia and carefully timed gas dynamic pressure waves, these induction systems ram additional air into the cylinders. This so called "Natural Supercharging" effect results in increased torque. Mainly midrange torque improves, right where the street rider needs it most. Dual Bore Tuned Induction systems can be used in combination with any programmable Fuel Injection module with enough capability and tuning range, such as the S&S VFI module ZPN750058 or ZPN750859. Dual Bore Tuned Induction kits are available in chrome, burnished and black powdercoat finish and fit the S&S dual bore throttle bodies only. Dual Bore throttle bodies for most Big Twin and Twin Cam models are available upon Special Order, please check with your Zodiac dealer.