I will say this right now… There is nothing wrong with the stock system that comes on the 2023 YZ450F. The headpipe and mid pipe are different than the 2022 machine so FMF went to work and built a system that helps that mid range hit that the 23 YZ450F has. Unlike last year, where the YZ450F was touchy down low (on low rpm), the 23 YZ450F has a smoother low end/low rpm build but the mid range comes on hard and can take you by surprise when you start to get fatigued. You can tone it down via Yamaha Power Tuner with the Control Torque Map (see my website for maps) but the FMF makes the ramp up to the mid range a little smoother. It’s like the FMF 4.1 slip on system fills in the gap between the bottom to mid range. Compared to the stock power, the FMF 4.1 muffler gives you a smoother low end power with more of a liner feel and kills the mid range hit a little where it can be easier to control coming out of corners. You might be saying to yourself, “it sounds like the FMF 4.1 muffler makes the 2023 YZ450F slower”, but that is not technically correct. It shifts the power in areas that makes the Yamaha more rideable for us mere mortals that purchased this fire breathing machine. Second gear roll on is more manageable to my throttle hand and the 4.1 system does have more connectivity to the rear wheel than the stock muffler and revs out just as far with more of friendlier pull into third gear. Connectivity is important and getting a muffler to give your YZ450F more rear wheel traction is important. Picture you massaging the throttle as you exit a rough corner. When you do this you want your engine character smooth so the rear wheel doesn’t spin as much and can drive through the bumps instead spinning on top of each of them. This FMF 4.1 allows the rider to be more aggressive with the throttle yet gain more traction that of the stock system! You will not be getting more lugability with the 4.1 muffler but going up to a 50 tooth rear sprocket can help you run third gear more in corners with this FMF 4.1 set up. You also will be losing a little over one pound with this system so for you guys that are counting calories, you can rejoice on the diet you just purchased. Also, I liked the 4.1 slip on with the insert IN as it was smoother and (to me) sounded better to the ear. For around 800.00 bucks this is a system that can help make the YZ450F more rideable as well as look better! Go to fmfracing.com to get yours, because they usually go quick!
