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Yoshimura RS-4 Features: 
Pentagonal-shaped sleeve
Front muffler cap functions as a polyresonant chamber which helps reduce noise
Two-stage stepped baffle
Turn-out carbon fiber end-cap
Stainless steel header and tail-pipe
 
RS-4 Stainless/Aluminium Full System:
The RS-4 is a unique design with predicated power and a quiet earthy exhaust note that speaks volumes for performance. This RS-4 features all the benefits of our original RS-4 muffler, but with a unique turned-out end-cap, designed to direct exhaust heat and gases away from the bike's components. To top-it-off, we embossed our Yoshimura's "347" logo in the carbon for a clean look.  With all its benefits in mind, the RS-4 was an obvious choice for the WR450F.
 
RS-4 Stainless/Aluminium Slip-on:
The work that went into developing the RS-4 muffler design paid big dividends in 2010 with Ryan Dungey winning the AMA 450 Supercross and Motocross Championship series as a rookie in the same year, and again in 2012 with the Yoshimura-backed GEICO Honda team winning both 250 Supercross Lites titles. That same R&D has been directed to developing the current generation RS-4 — a unique design that provides an unrivaled combination of power and a quiet exhaust note. The RS-4 features a Polyresonant duplex chamber, a two-staged stepped baffle and an innovative carbon cone end cap.