The ThunderMax ECM Performance Auto Tuner For Harley is the high-tech way to manage every aspect of your fuel curve for the best throttle response and performance possible. It mounts conveniently in place of your factory ECM and plugs into your existing harness, and uses a closed-loop control system to continuously self-adjust your motorcycle's air/fuel ratio in real time while your ride! If you start at sea-level and ride up to a mountain pass, the ThunderMax will automatically adjust your tune to keep your engine running cool and happy!