Product Report: FMF Factory 4.1 RCT Exhaust

The FMF Factory 4.1 RCT system for the 2013 Kawasaki KX450F is based on the same system that Ryan Villopoto used to win last year's Supercross and National Championships, but tweaked a bit, just to meet the new needs of the '13 bike.



PRICE: $899.99

APPLICATION: All modern MX bikes (tested here on 2013 Kawasaki KX450F)


The Factory 4.1 System incorporated the latest in FMF Resonance Chamber Technology both internally and externally. It starts with a new core – a patent pending shape enhances and refines the exhaust pressure wave for optimal power output while lowering the sound level. In addition, we achieve a shorter overall length that is less susceptible to crash damage and complementary to our Factory Forward Engineering – moving the muffler closer to the motor to centralize mass.┬áVisible changes to the exterior include a redesigned canister to increase internal capacity for the maximum volume of packing material. The packing itself was not overlooked - a proprietary blend formulated for superior durability and sound attenuation. The final component is a new rear endcap engineered for simple tuning adjustments incorporating a snap ring feature to secure the standard and optional inserts. The Factory 4.1 RCT is constructed from only aerospace grade materials that meet our exacting specifications and is manufactured 100% at our Southern California factory.

Our test unit came equipped with a prototype Megabomb heat shield, like the one used by Andrew Short on his L&MC Honda CRF450R. Though the carbon fiber shield is not yet available, it is expected to reach production in the near future. Personally, we've never had a problem burning our boots or pants on the Megabomb, but the shield is a nice touch, anyway.


– As always, the quality and fit of the Factory 4.1 RCT System was impeccable. The system bolted right on to our 2013 Kawasaki KX450F test bike in minutes, and required no pushing, pulling, or coaxing.

– We don’t spend much time on the trails or in the desert, but if you do, a USFS-approved spark arrestor is included. Bonus points for including it in the bag, and not installing it in the system as delivered. (Then, we’d have had to remove it!)

– Available in anodized or natural finishes. The blue anodizing is pretty sweet, and it compliments the blue accents of the new KXF.

– In the Kawasaki KX450F’s case, the FMF system is actually quieter than stock. KX450Fs are among the loudest stock bikes on the track, and the 4.1 system gives it a deeper, less offensive exhaust note.

– Constructed of titanium, the system offers several pounds of weight savings over stock.

– Power is improved throughout the powerband. This is apparent from the second the bike is fired up, as throttle response and snap are noticeably improved.

– The low-end punch of the stock KX450Fis actually smoothed out and broadened a bit, making the new 2013 powerband a bit easier to control.

– Mid-range power is strong and broad, and the bike can be ridden very effectively in a taller gear.

– The 2013 bike has a little less overrev than the 2012 model, but the FMF system recovers all that was lost. Our test bike pulls to the moon.

– The carbon fiber end cap has a very factory look about it.

The header pipe of the FMF system is fatter than stock, making for better mid-range and top-end pull. As opposed to the stock header that is held in place by two nuts and a flange, the Megabomb header utilizes a two nuts, a flange, and two springs. This design is geared towards greater durability, as the "floating" mounting system is less prone to breakage from vibration.


– We’ve got a Honda-powered pressure washer that can blow the warning labels off the rear fender, and the FMF label on the muffler fell victim to it during its first wash. Though it didn’t blow completely off, the corner lifted and that’s the start of “The Naked Truth.” FMF should supply an extra muffler badge or two.

The Factory 4.1 muffler is tucked in better than stock, thereby improving the look of the bike and centralizing the center of gravity, too.


As you can tell, the only complaint we have about the FMF Factory 4.1 RCT System is that the muffler sticker comes off. That said, 2013 Kawasaki KX450F owners that are looking to quiet down their new bikes while at the same time cutting weight, improving its looks – and most importantly – improving its powerband, should look no further. We tested a ton of exhaust systems on our 2012 Kawasaki KX450F test bike and the FMF reigned supreme. This model year could be more of the same…