Big Gun Evo/Eco Exhaust Packing Kits Big Gun mufflers are packing-style mufflers and do require maintenance. Extend the life of your muffler with this Big Gun Packing Kit. Features: Compatible with most current and older style Big Gun EVO and ECO series mufflers High temperature loose-fill packing material condensed into an outer casing Rated at approximately 15-20 hours of ride time Maintains noise levels without affecting power Keeps overall muffler heat down 15 or 17 size