Yoshimura KTM 450SX-F/HUSQ FC450 18-20 RS-4 Stainless Slip-On Exhaust, W/ Aluminum MufflerYoshimura KTM 450SX F HUSQ FC450 18 20 RS 4 Stainless Slip On Exhaust, W Aluminum Muffler KTM and Husqvarna have introduced LE and Rockstar Editions for 2018 and now Yoshimura is ready to add to the experience of these awesome dirt bikes. We developed the RS 4 in the R&D lab called the Motocross track. The RS 4 boasts its own resonance chamber and utilizes its volume and a unique baffling system to create the sound and power that is purely Yoshimura.