HMF 041353606071 Performance Exhaust: Yamaha Raptor 660 Fits: 01-05 Slip On Round Side mounts Turn-Down-Brushed End Cap EQUAL POWER: The Performance Series distributes power evenly throughout the entire RPM range. 4-6 dB INCREASE: Depending on the model, you can expect a 4-6 dB increase over stock. UNRESTRICTED CORE: The Performance Series uses a 2 1/8 non-restrictive core for maximum flow.