HMF Honda TRX 400EX 1999 - 2014 Red Slip On Exhaust Muffler & Jet Kit + UNI The Performance Series uses a 2 1/8" non-restrictive core for maximum flow. Depending on the model, you can expect a 4-6 dB increase over stock. The exhaust shell is made of T6061 Aluminum that weighs substantially less than stock. USFS Approved: All HMF offroad exhausts come with a USFS approved spark arrester. Included: Individual Keihin Hex Jets: 152, 160, 165, 170, 180, 190 and 42 Pilot