After countless hours of dyno testing, the NINJA400R Superbike Velocity Stacks are ready! The OEM Airbox in the Ninja 400 contains two different length velocity stacks, a long one and a short one. This kit replaces both stacks with our own spec shorter velocity stacks designed by Jeremy Toye. The performance difference with the Superbike Velocity Stacks compared to the stock is dramatic. The power curve with the stock setup falls off pretty fast after 9500 RPM, but with our velocity stack setup, it continues to climb all the way to 11,800 RPM, maximizing power for high RPM track use. For maximum performance, it is recommended to use our Superbike ECU flash or aRacer RC2 ECU with the new velocity stack setup to correctly tune each cylinder to the new Velocity stack lengths. Here?s a dyno comparison with a stock motor and stock airbox vs modified airbox (snorkels removed) with Ninja400R velocity stacks. You can see the power band carries strong almost all the way to red line instead of falling off at 9500 and we don?t lose any important midrange power. *We strongly recommend using our Norton Racing ECU flash or an aRacer RC2 race ECU paired with the new velocity stacks. We have re-tuned each cylinder to match the new velocity stack lengths for maximum performance and reliability. *If you have already purchased our Norton Racing ECU Flash for your bike and now you want to install our Superbike Velocity stacks, please contact Norton Motorsports to update your ECU mapping.