FMF Racing needs no introduction when it comes to dirtbike performance.

FMF Racing
FMF Racing'south Factory 4.ane RCT sideslip-on muffler performs fifty-fifty better than it looks. And it looks awesome.

FMF Racing founder Don Emler Sr. is 1 of the pioneers of aftermarket dirtbike frazzle systems, starting in the ii-stroke era of the 1970s. Nether his guidance, FMF has always been ane of the premier pipe and muffler builders in the industry, and that never changed fifty-fifty after the sport evolved to hyper-performance 4-stroke motocross and off-route machines. The company is relentless in its pursuit to pull more horsepower and torque out of every stock machine no thing how well-developed the stock engine/pipe combination. Sideslip an FMF Racing piping on your stock automobile, and it's a prophylactic bet that you're going to become faster.

So when FMF Racing promised massive horsepower gains throughout the rev range with its Mill four.i RCT muffler, we wanted to know simply how much constituted massive. Afterward all, if you're shelling out nearly $400 for a muffler, you want to get what you're paying for.

To the uninitiated, the RCT in the Factory 4.ane RCT muffler'due south nomenclature stands for Resonance Chamber Engineering, and FMF trademark design that incorporates a muffler core shape that alters the frazzle pressure level wave for maximum power output while minimizing frazzle noise every bit much as possible. The RCT also helps FMF to create mufflers that are shorter in overall length, which helps to constrict them in toward the front of the motorcycle. Mass centralization is a bonus, only the key do good, according to FMF, is that the muffler volition be less susceptible to crash damage FMF Racing Factory 4.one RCT mufflers are constructed from only aerospace grade materials that meet the company's strict specifications, and they are all manufactured at FMF'south Southern California manufactory.

FMF Racing
Our Factory 4.1 RCT dyno flog took place at Mickey Cohen Motorsports in Placentia, California.

We were anxious to put a Factory 4.i RCT muffler to the examination, and it just so happened that nosotros had access to 2017 Husqvarna FE 501 that could serve as our exam mule. Right away, it should be noted that the FE 501 is a dual sport motorbike and therefore is field of study state and federal emissions regulations. Thus, nosotros do not recommend swapping your stock dual sport muffler for any muffler that does not run into those regulations. In the dirt, still, it's some other matter entirely, and since this was purely a dyno thrash on our role, nosotros were curious to know if FMF could deliver on its claims.

While our test bike was fitted with a lot of trick-looking accessories, the engine was stock except for a minor ECU mod that is identical to Euro-spec Husqvarnas. We selected Mickey Cohen Motorsports of Placentia, California, to handle the dyno testing of the Manufacturing plant 4.1 RCT muffler for united states. In addition to running a complete motorbike repair shop, owner Mickey Cohen is besides the manager of Triumph Motorcycles' westward coast motorcycle fleet and a former AMA Pro Thunder Championship-winning road racing tuner, and so he knows what to look for when it comes time to squeeze more than power out of a iv-stroke engine.

Right off the bat, our baseline test showed that the FE 501 is no slouch in stock course—even if it is Euro stock. Our test machine churned out a solid 39.three rear bike horsepower @ 8100 rpm with a height torque figure of 28.4 lb.-ft. coming in at 6300 rpm. What's impressive is that the Husky motor makes over 20 lb.-ft. from 4400 rpm all the fashion to 9100 rpm before only gently dipping below that every bit the engine reaches its 9700 rev limit. Those our stout numbers that only reaffirm our belief that a 500cc is just about the platonic displacement for a 4-stroke Unmarried.

Still, we had no incertitude that the FMF Factory 4.1 RCT muffler would enhance the Fe 501'southward power output. We merely had no thought past how much.

Swapping the Manufacturing plant 4.ane RCT muffler onto the stock Husqvarna header was like shooting fish in a barrel, as FMF supplies a slip-on collar that matches the muffler's larger i.d. with the header'south smaller o.d. The Factory 4.1 RCT is so installed using the grommets, spacers and bolts from the stock Husqvarna muffler. The whole process took only a few minutes once the stock muffler was cool enough to handle. Another do good of the Manufactory 4.1 RCT is that information technology is substantially lighter than the stock muffler. FMF supplied u.s.a. with its stainless slip-on model, only an even lighter titanium version is also available. We were glad to see that our test sample came with the carbon fiber end cap, which adds to the muffler's already trick appearance. FMF besides ships all of its Factory iv.1 RCT models with a USFS-approved spark arrestor for off-road employ (in search of a max power gain we opted not to install information technology). FMF claims to use the highest-quality proprietary blend stainless steel in the Factory 4.1 RCT.

FMF Racing
As y'all can see by the numbers and the curves on our dyno graph, the FMF Factory RCT 4.one delivers a substantial gain over the stock muffler without sacrificing the stock ability character.

That'southward all well and good, only what kind of ability does information technology make? The answer is… a lot. Once fitted with the Manufacturing plant 4.ane RCT, the Husqvarna's exhaust burble sounded a whole lot healthier at idle, and it delivered a radical though non overly piercing roar every bit Cohen hammered the throttle to record the dyno run. The Atomic number 26 501 responded to the Manufacturing plant 4.1 RCT by pumping out 43.6 rear bicycle horsepower at the same 8100 rpm as the stock muffler while peaking with 30.9 lb.-ft. @ 6100 rpm—200 rpm before than the stock muffler. That'south 4.2 additional horsepower and two.5 lb.-ft. of additional torque at the peaks, but taking a await at the dyno graphs, you can also see that the Factory iv.1 RCT basically mimics the stock horsepower and torque curves. There's simply more power everywhere!

Going through the gears, there's simply no mistaking a stock Husky FE 501 when compared to an FMF Racing Factory 4.1 RCT-equipped version of the aforementioned machine, all other things being equal. The skid-on makes a huge difference in both grunt and steam throughout the rev range, delivering as much every bit 10.six percent more power along the fashion. Fifty-fifty the usually skeptical Cohen agreed that the FMF Factory iv.i RCT delivered an impressive power gain.

The FMF Factory iv.1 RCT muffler in stainless steel (as tested) for the Husqvarna Atomic number 26 501 retails for $399.99 while the Ti version retails for $499.99. That may sound similar a lot of money, but considering that this, like other FMF products, delivers on its promises, we'd call information technology a hell of a bargain.

FMF Racing

FMF Racing Factory 4.1 RCT Muffler, $399.99 (stainless w/carbon fiber endcap)/$499.99 (titanium due west/carbon cobweb endcap)
FMF Racing
18033 S Santa Iron Ave.
Rancho Dominguez, CA 90221-5514
Phone: 310-631-4363
Website: world wide web.fmfracing.com