By: Dominic Cimino
Any of you that stay up to date with us here at Keefer Inc. are aware that I really enjoy riding the 2019 KX450. Like I really enjoy it. Maybe it is because we have the chassis and suspension dialed in just for me or maybe it’s just because the bike is so damn fun. Either way, I am excited to continue making improvements to this bike in the upcoming months because every time I ride it I feel faster. Next on the chopping block is the motor department and we decided to start with exhaust first. I wanted to test the RS-4 Stainless Steel Yoshimura system because I have had great luck in the past using their systems on other bikes and the guys over there always take great care of us.
Yoshimura exhaust systems are made from scratch right here in Southern California. Their R&D facility houses everything from the race team shop, dyno/engine rooms, to the space where they lay all of their own carbon fiber. The attention to detail and quality of product is top notch in everything they produce and to give you a little more background on Yosh, you can watch this short clip:
https://www.youtube.com/watch?v=V5J5kltNfvQ
Although it is a couple years old and mainly showcases road racing disciplines, trust me when I say that it all translates equally into motocross. You can sleep peacefully knowing that your investment is going to be worth it.
The stock exhaust system on the 2019 KX450 is not too bad overall. Beside it looking really bad (that is a no-contest) and weighing a decent amount, it produces a good tone and useable power. I think this exhaust compliments the motor and power delivery well by keeping things linear and quick revving - one of my favorite traits about this bike overall. But on the flip side, the motor does lack some “meat” in the RPM range and the over-rev tends to sign off relatively quickly at the top. Installation of the new Yosh was quick and easy with every single piece fitting in place perfectly. I love when that happens! The stainless/aluminum system that I tested weighed over a pound less than the stocker and comes in at a fair price of $675.78. In roughly ten minutes, the KX looked better instantly with the new system in place, and when I pushed the button to wake her up, she sounded healthier too. I am not a fan of obnoxiously loud exhaust systems so I was happy to listen to the Yosh when cracking the throttle on the stand. Definitely louder than stock, but not deafening.
Before installing the new Yoshimura system, I did a couple morning motos at Glen Helen to get the best gauge of the stock comparison. The most obvious difference when cruising back onto the track was the tone, as it has a deeper/healthier sound. But when in stride, the exhaust made the KX come to life from the mid range and beyond. The linear power curve stayed true on delivery, but exemplified a more crisp powerful feel when on throttle. I felt the Yoshimura system was able to harness a little more “meat” that I have been searching for and also helped push the bike into the higher revs more efficiently. On the top end, over-rev was increased quite a bit as the KX seemed to pull longer and harder overall. I noticed when charging down Mt. Saint Helen I could hold 2nd gear almost half way down the hill before hitting the limiter. The stock exhaust would sign off way earlier than that in the beginning part of the day. I also realized I stayed in 2nd gear almost all the way around the Glen Helen circuit. This is a testament to the linear power I have been talking about on this 2019 KX450, and the Yoshimura system makes it even better. Where I didn’t notice a substantial improvement was bottom end power delivery. The KX is not a torquey bike in stock trim by any means, but I was expecting to get a little more bark with the new system. This was not the case and I found myself clutching the bike in the soft corners to wake it up in order to get back into the mid range, where I think it excels.
Overall, the new Yoshimura exhaust system is a great performance improvement to this already great bike. Looks good, sounds good, and runs good - thats what it’s all about, right? Obviously, I am going to set my sights on continuing to improve the power delivery to round out this new KX450. I am happy with the mid/top end feel, so maybe we can experiment with new map settings to get a little more lovin’ down low. As always, stay tuned for what is next here at Keefer Inc. If you have any questions about the 2019 KX450 please feel free to email me at dominic@keeferinctesting.com. Or you can head over to Yoshimura-rd.com to see what they offer for your green machine.