Yoshimura 2010-2011 yz450f rs-4 Ti Full System - Dirt Rider Magazine

It's amazing how much we were able to tune and move around the power delivery with just the Yamaha Power Tuner on the '10 YZ450F. Yet there was that point in which I made improvements but was still seeking changes in several areas. The first was overrev, the second was a little more oomph between second and third gear. I had already added some fuel and retarded the ignition down low to help smooth the transition right off idle to the hard-hitting YZ-F power. This helped, but in deeper soil there was still a slight gap between second and third, and I yearned for an extended top-end. I first considered adding a tooth to the rear sprocket but then started to hear some good things about Yoshimura's RS-4 exhaust and decided gearing was probably not the answer because of the hard-hitting bottom-end. It took a few months to save up for the $995 unit before it was possible to finally hit the Add to Cart button.When the Yosh system arrived, I marveled at the craftsmanship and beautiful welds in the all-Ti system with carbon fiber end-cap. The new three-piece plumbing bolted right up in no time. The sections secure to the stock exhaust mounts and the pipe unions are held in place with the supplied springs.

To start the test I put everything back to stock with regard to fuel injection and ignition timing. On the track it didn't take long to understand the changes the Yosh exhaust made to the power curve. First and foremost is the top-end performance. Instead of going flat and signing off, the Yosh helps the power run a lot further up the ladder before tapering off. This alone helped fix the issues with second- to third-gear gaps. Now I was able to hold second further in the rpm range and shift deeper into the power curve going into third.Second, even with the stock ignition and fuel settings, the low-end is a lot smoother, which makes the bike easier to ride. It is almost as if the Yosh exhaust took over where the Yamaha Power Controller left off. And with the controller you have even more when it comes to tunability.The RS-4 puts out a nice note and is capable of getting down to 94 decibels with the optional AMA insert. With the insert installed we were not able to tell the difference between the two on the track. Looking like a piece of motorcycle art, the Yosh is not a cheap addition and, to some, a hard pill to swallow at nearly a grand. Yet in the end, I did not regret the purchase since I planned on keeping my 2010 for a second season, not to mention I am digging the newfound performance and ease of riding.

Hard Parts 92.0 Installation 20/20 Function 46/50 Durability 9/10 Design 10/10 Price 7/10 www.yoshimura-rd.com 909.628.4722