Spec II is a specially designed system for competition use only. Its simple straight thru design creates an increase of exhaust gas velocity in order to improve efficiency. The middle silencer (resonator) on the main pipe is designed to maintain torque in the low to mid speed range. All mufflers are made with SUS304 stainless steel, 1mm is used for main pipe. and the ultra 0.8mm is used for main silencer. This combination creates a super lightweight muffler. Mounting hardware, gaskets, and inner silencer is included with all systems.