The 2026 Yamaha YZ450F has seen some changes to its engine character. With a new muffler that is a 109db system that all manufacturers will have to adhere to. Yamaha also changed the port sizes in their head and put a resonance chamber inside the air intake to help with sound regulations incoming. With all that being said FMF set out to make a new 2026 YZ450F 4.1 RCT muffler system and we got one of the first to try.
The Factory 4.1 RCT incorporates the latest in FMF Resonance Chamber Technology™ both internally and externally. In addition, FMF achieved a shorter overall length that is less susceptible to crash damage and complementary to their Factory Forward Engineering – moving the muffler closer to the motor to centralize mass. The Factory 4.1 RCT is constructed from only aerospace grade materials that meet their exacting specifications and is manufactured 100% in the Southern California factory.
First off, yes the FMF 4.1 does weigh almost 1.5 pounds less than the stock system so you will be trimming some weight off of your bLU cRU. The exhaust note is also much less raspy/loud sounding than the older 4.1 version as this new 109db FMF 4.1 muffler has more of a deeper sound with a slight whistle to it. It sounds way more “professional” to me than the older version did. I also know that the YZ450F likes some back pressure so having a muffler that has some back pressure and not just a wide open hole through the perf/core of the muffler, works much better out on the track (on the Yamaha at least). The new FMF 4.1 RCT system gives the Yamaha more rear wheel connection than the stock system and wakes the power back up, similar to the 2025 power. The difference between the 2025 engine character with the 4.1 muffler system installed and this new 2026 version is that it has a smoother pulling power down low, yet gives this 2026 YZ450F a longer feeling second gear. With the 2026 YZ450F incorporating a 13/51 final drive gearing spec, second gear was a little short at times. With the FMF installed, it woke up the low RPM feel in second gear and allowed me to pull that gear longer down the straights. The FMF 4.1 system for the 2026 YZ450F allows the rider to run a 50T rear sprocket instead of the 51 tooth. The added low end pick up and longer pulling power gave me enough confidence to run the 13/50 gearing with good results at every So.Cal track as well as a couple Georgia tracks I have ridden.
With the FMF 4.1 RCT system installed you will gain more low to mid range pulling power but I didn’t notice a ton more top end pull. I do get a small amount of added over rev feel (maybe because the smoother/torquey power delivery gave me a slightly slower spool up, which was a good feeling. Once you install a 50T rear sprocket on you will notice a little more top end pull but this is still a YZ450F people so I don’t think we need a lot more top end pull. She is fast enough, I am just looking to spread out the power to make it an easier blue bike to ride. George and the crew at FMF did a great job of developing a muffler system that delivers a power character that is increased over stock yet smooth enough that it is ridable. Nothing worse than a on/off type of engine character because the aftermarket muffler has a huge sized core. I think this is one of the better systems FMF has built in sometime for the YZ450F. Even though I run an Akrapovic most of the time on my Yamaha YZ450s, this has me thinking I might keep an FMF on my bike. I just want my muffler packing to last more than 12 hours!
If you’re in the market for a muffler system for your new 2026 YZ450F this FMF system is a step better than the older 2023-2025 version and it will set you back $1375.00 for the full titanium system. The good news is that you will be able to feel on the track where your money was spent. Is it worth the money? That depends if you want the engine character I mentioned above. If you do, then yes it is worth it. If you’re happy with your stock engine character, keep living your life but thanks for reading this review anyway. You can order yours now over at fmfracing.com. Maybe Steve has a discount code?
