The FXR ThunderheaderHarley ThunderheaderThunderheader exhaust systemsetupunit consistently receivesgarnersearns rave reviewstestimonialspraise for its distinctiveaggressivepowerful sound and noticeablemeasurablesignificant performance improvementsgainsenhancements. Many ridersownersenthusiasts describe the tonesoundrumble as a deepthroatyresonant