I felt that I needed one after putting on my two brothers exhaust because I lost some of my top end power because I was running to lean. I installed the Dobeck ejk 3.5 and it seems to have worked. The upgrades in exhaust and ejk have made my 800 a beast on the low end. I am going to install my new uni air filter this week and see how the mods affect my top end. Can't wait.