FMF Stainless Steel Aluminum Factory 4.1 RCT Full Muffler System – Product Of The Week

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FMF Stainless Steel Aluminum Factory 4.1 RCT Full Muffler System (for 2016 Yamaha YZ450F)


The engine character is so useable we were leery to bolt on anything new that might change the power delivery of “big blue”. That being said, we were curious to see if in fact FMF Racing did their "testing homework" and built a better muffler (than stock) for the 2016 YZ450F. Which is tough to do these days, due to the stock mufflers being designed so well.

We got our hands on a FMF stainless steel Factory 4.1 RCT full system and bolted it up in less than fifteen minutes. Installation is very simple, but you will have to use your existing stock heat shields (FMF does offer carbon fiber heat shields for $99.99) and use some hardware that FMF provides to bolt on the rear can. The FMF system provided slightly less exciting throttle response, but gave the bottom end a smoother, even more controlled feel out of corners. This isn’t a slower feeling (out of corners) by any means, but with the FMF muffler system installed the rear wheel feels better connected to the ground. There is more traction to the rear wheel out of hard pack corners when you roll on the throttle. Mid range pull surprisingly is better than stock as second and third gears can be stretched out slightly further down straights. The stock Yamaha engine character with the stock muffler has no problems carrying third gear around most corners and the same goes for the FMF 4.1 Yamaha power character. But, as we rode the stock muffler system and the FMF 4.1 RCT system back to back on several occasions, we could carry third gear through very tight 180-degree corners with the FMF system. The stock muffler had a slightly tougher time to get the rpm’s back up (in third gear) and let you accelerate hard upon exiting. Mid and top end RPM response is improved over stock, as the Yamaha is quicker to react to your throttle hand. Top end and over-rev is slightly improved (not that you need more) and you can really feel the top end pulling power when the track is tilled up really deep. The stock system feels somewhat empty on top compared to the FMF system, where the 4.1 will still pull hard.

The FMF 4.1 RCT did give us more de-cel pop than with the stock muffler installed. We immediately went to a richer map setting (that I found on Yamaha’s website) with the GYTR Powertuner and it cured any de-cel issues we had. Even though the FMF system is aluminum you will be saving a couple pounds to your YZ450F. The stock muffler system weighs in at 9.1 pounds and the stainless FMF system weighed 7.5 pounds. The durability of the FMF aluminum system has been superb as it has endured over 20 hard hours and is just now showing signs of a repacking job. The FMF aluminum muffler is not as attractive as the blue titanium version FMF offers, but at $799.99 it is almost $300.00 cheaper.

We were impressed by the FMF system’s performance, as it is very hard to match, let alone surpass the manufacturers stock muffler’s power delivery. We are very happy to trade the heavier stock YZ450F muffler in for the FMF stainless steel aluminum 4.1 RCT muffler system. It is a full muffler system that does more than look good, it actually works better than the stocker!

FMF sells carbon fiber heat shields for $99.99 or you can just use the stock aluminum heat shields like we did.
The muffler still incorporates a carbon fiber end cap design.
The Stainless Steel/Aluminum FMF 4.1 RCT Full System delivers on the horsepower.