Yoshimura RS-4 Stainless Full System

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What is the first thing that many riders do when they get a new bike? Throw a new pipe on it. Well, just like the people who buy exhaust systems, the companies that make them are also some of the first to the draw in offering products for new models when they first become available. There a few redesigned motocross machines hitting the market for 2014, with the new Yamaha YZ450F standing out as one of the most revised from its previous version and Yoshimura was one of the first companies to make a pipe for the blue big-bore.

There is a common belief that many exhaust specialists make pipes simply because they know their product will sell well, despite minimal performance gains. This may be true in some cases, but not with Yoshimura. In their eyes, there is no point in making something that is not going to improve a bike’s power output. So when the folks at Yoshimura gave us a ring to come try out their 2014 YZ450F, I was excited to see how they could improve upon the Yamaha’s already impressive power plant.

Of course, being an exhaust company that also runs several factory race teams, Yoshimura does not cut corners. So, along with two different systems to at the ready, their 2014 YZ450F came outfitted with DeCal Works graphics, black Excel A60 Rims fitted to blue Talon Hubs (by Dubya), Yoshimura engine plugs and brake clevis, and a Hinson Racing clutch. It’s amazing how a few simple items can vastly improve the look of a bike. Stock bikes, no matter the OEM, tend to look tame. The Yoshimura 2014 YZ450F looks like a race ready machine.

But, the purpose of riding this machine was to test their new exhaust system. For this model year, Yamaha went to a new header pipe that wraps around the cylinder, allowing them to still take advantage of the rearward facing exhaust port while maximizing this year’s most popular buzz phrase, “mass-centralization.” As a result, the end of the stock exhaust can has moved seven inches closer to the motor over the 2013 version.

On track the stock 2014 YZ450F is a potent machine with a good, broad powerband that starts with strong, yet smooth bottom-end, continues with a meaty mid, and carries into the upper ranges with a moderate pull. For this year, Yamaha increased the RPM limit by 250 to help the top-end power, but the bike still has a tendency to fall off slightly as it reaches higher RPMs. Yoshimura essentially sought to improve the overall performance of the exhaust system; to add a bit more grunt throughout the powerband, but still allow for usable power throughout.

When testing the new RS-4 system, Yoshimura also had their slip-on pipe available along with the original stock unit for comparison. First using the slip-on can, I noticed an improvement in the mid- to upper RPM ranges over the stock pipe. Where the stock unit would begin to sign off a little earlier than desired on the steep Glen Helen hills, the RS-4 Slip-On allowed the YZ450F to pull a little bit longer in each gear, effectively allowing fewer shifts. However, the bottom end power was basically unchanged.

This is where the RS-4 Full System comes into play. Heading back out onto the track, the bottom-end power was immediately noticeable, with a bark that caught me a little off guard, simply because I had become accustomed to the gradual build in power of the stock system. The RS-4 full system provided the 2014 YZ450F with a much broader powerband, combining that initial snap with the improved mid- to upper-mid RPM performance of the Slip-On system (the RS-4 Slip-On and Full systems actually utilize the same exhaust can).

In true Yoshimura fashion, the RS-4 two-piece header pipe is a thing of beauty, with excellent welds, precise machining, and fitments for the two stock pipe guards that come on the 2014 Yamaha’s (since the wraparound pipe routes on both sides of the cylinder the new YZ450F uses two pipe guards as opposed to one).

Overall, the RS-4 Slip-On and Full Systems offer performance gains over the stock system. While the Slip-On has moderate improvements in limited ranges, the Full System offers noticeable power benefits throughout the RPM range. If you are in the market for, or already have a 2014 YZ450F, the new RS-4 systems might be what you’re looking for.

Yoshimura offers the RS-4 in four different versions: the Slip-On is only available in aluminum steel ($425.00), while the Full System is available with a stainless steel header and aluminum muffler ($725.00), titanium header with titanium muffler ($995.00), or titanium with carbon fiber muffler ($1095.00). All of the Full Systems offer the same power gains for the motor, so it all comes down to how light you want your system to be.

For more information, visit www.yoshimura-rd.com.

-Bayo Olukotun