A harmonic Dampener is something that reduces engine vibration throughout different RPM ranges. Now my ME skills are coming back. Basically, an engine has a certain vibration to it and when you increase the RPMS, that vibration has different characteristics, meaning that it will increase or decrease. The engine has a certain harmonic frequency and when it is lower or in balance, you are not losing energy and you will save more HP, just like adding a light weight flywheel, you free up horsepower. The harmonic dampener is meant to counteract vibrations and provide a smoother revving engine throughout the RPM range thus saving you HP.