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We recently took delivery of FMF’s 4.1 slip on muffler design to put on our 2024 Kawasaki KX450. FMF is offering a full and a slip on design but for the time being let’s talk about the slip on version. FMF’s slip on version will shed almost 1.5 pounds off of the rear of the Kawasaki and to me isn’t too long like previous FMF mufflers. I know most of us like that short muffler look that is tucked up behind the side panel but if you make a muffler shorter, not only can it get louder but it also can hurt power delivery/character. Having some length to the muffler (or headpipe) will create a longer power delivery that is more usable than a shorter system can.
As you know Kawasaki left a lot on the table for the aftermarket muffler companies this year and this FMF 4.1 slip on is much better than the stock KX 450 muffler system. The FMF 4.1 delivers more low end pulling power out of corners yet keeps that smooth/linear pull. Installing the 4.1 doesn’t give you all this hit down low, yet it delivers more usable pulling power in second gear. There is more torque feeling out of corners and also makes the KX450 feel a little more playful through the bumps. Simply addling this FMF 4.1 slip on can allow the rider to hop over bumps better as well as give a better throttle to rear wheel feel on hard pack areas of the track. Sometimes the stock muffler delivers such a smooth power that it requires the rider to use more throttle and then (at times) can give the rider more rear wheel slip because of a disconnection between how much throttle is twisted versus how much power the KX450 is actually delivering on the track. With the FMF 4.1 slip on installed, it gives a much more accurate feel when twisting the throttle in comparison to the rear wheel. We call that “throttle to rear wheel connection” in the production testing world. The mid range pull is also increased and makes third gear more usable in corners. This isn’t your Yamaha type of power where third gear is usable around most of the track but it does make the KX450 a little more third gear corner friendly. 2nd-4th gear top end pulling power is slightly increased (not as noticeable as low to mid range) but to me I didn’t need more peak horsepower out of the KX450. I am looking for more usable bottom to mid range and the FMF slip on delivers that to the rider.
If you’re in the market for a little more usable power out of your green machine, the FMF 4.1 slip on is not a bad choice. For $899.99 this muffler will actually change the power character of your Kawasaki. Not often do we get an aftermarket muffler that you can actually feel where your money went. Kawasaki has allowed the aftermarket to make huge gains and FMF has created a muffler to add to your KX 450 delivery.
