We all know Kawasaki left a lot of room for improvement on the muffler side of things on the Kawasaki KX450. We have tried a number of mufflers to help increase the low end torque and have been happy with a couple. The latest muffler we tested was the new Yoshimura RS-12 stainless full exhaust system. First and foremost the fitment was top notch as we had zero trouble installing this system on the green machine. The stainless system is a little heavy out of the box and it weighs in at 8 lbs. 3 oz. That is almost two pounds heavier than the stock system! We can’t say we noticed the weight on the track as it didn’t negatively affect the handing of the KX450 so you crazy vet riders should try to lose a few pounds on our own bodies before “we” complain about the weight of a muffler if it doesn’t negatively affect the machine.
We will tell you the overall power was an improvement compared to the stock system. The increased low end torque of the Yosh RS-12 helped the KX450 exit corners header which actually made the chassis feel better because we could get on top of the bumps better. Instead of being inside the pockets of the acceleration chop, the KX450 with the RS-12 system can ride over the top better and relax the rear end of the machine. All of this because the KX450 didn’t feel as lazy with the Yoshimura muffler as it did with the stock system. The KX450 still retained the smooth delivery like the stock system provided but with more torque feel and more mid RPM throttle response. I never felt any huge spikes in power or any hard hits, which we normally like out of our bikes but in this case it was nice to have a linear feel when the track goes south. We have been riding the 2026 Yamaha YZ450 and when we got back on the KX450 we remembered why we like the linear power at times. However, the stock KX450 is “too linear” for most so adding the Yoshimura system helps give us a little more “meat” that we need/require when it comes to a power delivery that were like. The increase in mid to top end power was slightly improved over the stock system but we felt the low to mid range is more where you notice the difference when riding your local track.
The exhaust note is deeper yet a little quieter than the stock system and of course the Yoshimura quality is as good as Akrapovic so you know this system is going to last you a while. Yoshimura also offers a repacking service just in case you don’t want to do the work yourself but if you do, they offer a full repacking kid as well as individual parts for the RS-12 system. For $1099.00 we personally think this is a great buy for the performance that you’re getting. The look of the muffler is a little big out the back of the bike but it grows on you. It did on us. Even though Yoshimura may not be well known for their KX450 muffler systems this system works well, is well made and a system that you will actually be able to feel where your money went. Any questions about this muffler system reach out to me at kris@keeferinctesting.com
