What It Is
Thanks to its association with the factory Red Bull Honda Racing team, Yoshimura had a head start when it came time to develop an aftermarket exhaust for the exciting new machine. Yoshimura offers four different versions of their system, ranging from $395 for a stainless steel slip on, all the way up to the $895 top-ofthe- line titanium/carbon fiber version that they sent us.
Every Yoshimura exhaust that we've ever tested has fit perfectly, and installing the newest RS-4 on the CRF was no exception. The pipe fits beautifully, and the fit and finish of the unit is second to none. Power is noticeably improved throughout the powerband, but the snappy feel and instant throttle response is what we like most about the unit. The biggest gains are felt in the low-end and mid-range as the bike seems to pull a taller gear with greater poise. Thanks to the Duplex Resonance Chamber, which mirrors the stock muffler's "pre muffler" design, the Yosh system is not much louder than the stock muffler, in spite of maintaining the stock muffler's diminutive size. We tested with the 99 db insert installed, but the system also comes with an AMA Pro Racing-legal 94db insert.
At nearly $900, the Yoshimura system is not cheap! Lucky for most, the $595 stainless steel/aluminum version offers the same performance gains.
Anytime an all-new bike like the 2009 Honda CRF450R is introduced, aftermarket exhaust manufacturers scramble to produce a good bolt-on system. Thus far, the Yoshimura RS-4 is the best performing system we've tested, and we've already been able to try out quite a few.