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Yoshimura RS-4 Comp Slip-On Exhaust Review

Thursday, July 7, 2011

The Yoshimura RS-4 Comp Slip-On Exhaust is an easy and affordable way to add some engine performance to your dirt bike.
This year for Christmas I bought myself a brand-spanking new 2011 Yamaha YZ450F. I’ve ridden Kawasaki KX450Fs since their introduction in 2006, so I thought I’d switch things up this year and try something new. Nothing looks as trick as the unique, reversed-cylinder YZ450F. That, combined with Yamaha’s reputation for quality prompted me to make the switch.
 
Friends warned me that I was going to miss the power of the KX after switching, but I figured 450s are too fast for the vast majority of riders anyway so I wasn’t overly concerned. From the very first ride, I completely understood what they were talking about. Although the YZ has crisp throttle response and packs a solid punch in the mid-range, the power signs off way too early. In the heat of battle, this can force a rider have to choose between making an additional shift at the end of a straightaway or risk being overtaken by a rider on a bike with more revs. I immediately set out to try to fix this problem.
 
First I tried several different ignition and fuel injection maps. All of these changed the delivery of the power, but none of them would help me rev harder and pull further in each gear. I figured the next step was to try a new slip-on exhaust.
I’ve been racing motocross for nearly 20 years now and have put plenty of pipes on plenty of bikes, but as soon as I tore through the packaging and pulled out the Yoshimura RS-4 Comp Slip-On Exhaust, I was blown away by quality and finish of it. The welds on the stainless steel mid pipe are a works of art! Installation was a snap, with a perfect OEM-style fit. The shorter muffler and carbon fiber end cap really upgraded the looks of my new bike!
 
The RS-4 comes equipped with a spark arrestor and noise reducing insert that are mandatory for off-road riding. As an amateur motocross racer that rides exclusively at closed-course tracks with no noise restrictions, I tested the RS-4 with the spark arrestor and insert removed to take full advantage of any added power the RS-4 could deliver. Noise levels are increased, but it certainly isn’t obnoxious.
 


A Yoshimura slip-on muffler added top-end performance to our test rider’s ’11 YZ450F.
On the track, the RS-4 delivered exactly what I was looking for. The bottom end and mid-range power mimics the characteristics of the stock exhaust, and this is a good thing! The stock YZ450F’s power delivery is so crisp that I used the GYT-R tuner to tone down the hit to improve traction and make the power easier to manage. The advantages of the RS-4 weren’t felt until the revs increased. Not only was there a noticeable improvement in peak horsepower, but the biggest advantage of my new slip-on is in the form of additional over-rev.
 
The RS-4 slip-on delivered a 1.6 horsepower gain over the stock exhaust, and more importantly, spread that gain over a much wider range. On the MotorcycleUSA.com dyno, the stock exhaust crested the 46 horsepower mark from 8200 to 9100 rpm. The RS-4 slip-on stayed above that 46 horsepower level from 8500 to 10,200 revs. It is amazing that a modification as simple as a slip-on exhaust could deliver an additional 1000 rpm of peak power!
 
Not only did the RS-4 slip-on upgrade the appearance of my new dirt scooter, it delivered a performance gain that was exactly what the doctor ordered. I would consider the Yoshimura RS-4 slip-on exhaust a “must-have” accessory for any 2010 or ’11 YZ450F owner.

The Yoshimura RS-4 Comp Slip-On Exhaust are avaliable at Motorcycle Superstore.
MSRP: $394.95
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