FMF Racing PowerCore 4 Hexagonal Slip-On, Material: Aluminum 041514 When designing the PowerCore 4 HEX, 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 wont break the bank. Overall increase in power and torque. Durable stainless steel and aluminum construction. Space Age internal packing material for maximum longevity.