Standard Powercore 4: When designing the PowerCore 4, FMF looked at their top of the line products to deliver race-inspired performance at an economical price. The end result is a quality muffler with improved torque, increased horsepower and rugged durability all at a price that won't break the bank. Overall increase in power and torque. Durable stainless steel and aluminum construction. Space Age internal packing material for maximum longevity. Hi-Flo modular end cap. Internal shape of core uses Hi-Flo technology. Enhanced sonic evacuation provides for higher flow and increased power. Includes removable (most models) spark arrestor.