04-09 YAMAHA YFZ450: FMF Powercore 4 Slip-On Exhaust - 4-Stroke (10) 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&#39;t break the bank.Overall increase in power and torque.Durable stainless steel and aluminum construction.Space Age internal pac Not intended for street use.Detailed Specifications: Type: Slip-On. Configuration: Single. Construction: Aluminum.