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FMF Racing Factory 4.1 RCT Slip-On

Owner: brobbo
Added on February 29, 2016

FMF Racing Factory 4.1 RCT Slip-On Reviews FEATURED

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Average Rating: * * * * -
16 user reviews
Exhaust Slip-On / Silencers FMF Racing Factory 4.1 RCT Slip-On Brand FMF Racing
FMF Racing Factory 4.1 RCT Slip-On
Last updated on: Feb 23, 2013 11:28 AM

Price Range: $374.95 ~ $599.99 Check Prices

Rating Breakdown:
* * * * * (11)
- * * * * (3)
- - * * * (2)
- - - * * (0)
- - - - * (0)

* * * * *

I race a Canadian off-road series that has two simple requirements as it relates to exhaust: 96dB max and spark arrestor, NO EXCEPTIONS! Both of these requirements are hard to meet with the stock Yamaha YZ250FX exhaust, so I starting looking at my options. FMF has been a long-time ThumperTalk sponsor, so naturally I decided to see what they had that might fit the bill. Their stainless steel 4.1 slip-on seemed like a good option, but they were temporarily out. But to my surprise, FMF brought their "A game", offering to kick down one of the premium Titanium versions in exchange for my evaluation. :)

The FMF Ti 4.1 Slip-on for the Yamaha YZ250FX (also fits the YZ250F) is a direct bolt-on replacement for the stock silencer. Outside of being lighter in weight than the stainless option, there are no performance differences between the two. It comes standard with a spark arrestor and wash plug, but the optional quiet core is extra.



Installation is pretty much the same as stock with basic skills & hand tools in about 15 minutes. FMF does recommend a bead of high-temp silicone (not included) where the header and mid-pipe join to insure an air-tight seal. Everything lined up perfectly making for an even easier job. Installing the spark arrestor was a bit confusing at first, but after doing it once, it’s been simple ever since.

The finish of the pipe is a beautiful, raw Ti color. Nothing fancy, anodized, or over-the-top; simple and clean. I noticed no blemishes, burrs, or anything that didn't look well put together, just pure goodness.

Ok, let's get to the good stuff... how does it perform? First, my requirements for racing were met. Out of 5 sound checks, I passed all with ease with one official saying how quiet he thought it sounded. It didn't see how many dB it blew during testing, but passing was my only real concern. While not one of my requirements, a bonus is the weight savings over the stock silencer. The FMF Ti 4.1 slip-on shaves 2lbs. and another pound when running an aftermarket spark arrestor end-cap. The Ti 4.1 also slightly changed my bike's power delivery. A common complaint is that the 250FX is a little aggressive off idle and the Ti 4.1 smoothed that off-idle hit, making the bike a bit more manageable in slippery conditions. It also added a little more over-rev, giving the 250FX a bit more legs in each gear. For my preferences, the added over-rev is great, especially when you need to hold it on just that little bit extra to make that extra pass. I didn't notice any difference in power with the spark arrestor installed.

Pros :thumbsup:

  • Modular spark arrestor.
  • Tested at/below 96dB when racing.
  • Improved bike's power delivery.
  • 2lbs.+ weight savings.

Cons :thumbsdn:

  • Hit to the wallet.

Monk's Bottom-line :prof:
It’s hard to lose with the FMF 4.1 Ti Slip-on exhaust. Not only was it easy to install and fit perfectly, FMF met my requirements when it comes to our racing series. The added weight savings and power gains were equally welcomed. The Ti version exceeded my expectations, but I'm sure that I'd have been equally as pleased with the more budget friendly stainless steel version.

* * * * *

Really like it!

* * * * *

Awesome Exhaust
* * * * *

Single exhaust made a huge difference in power
* * * * -

:thumbsup:    I installed it on my 2014 YZ 250F.  It installed with no problems. I did notice the stock silencer has a factory dent on the side of it. It lookes like it was needed so it would clear the air box. The FMF is smaller and does not require a weird dent to clear the air box.
This muffler is a little longer then the stock muffler. ( About 2 inches) The FMF came with a screen insert. I chose to run without it.
My seat of the pants impression was it was louder and I noticed no power gain at all.  I swapped back to the stock muffler and back to the FMF at the track several times. I tried different fuel and timing maps. But I really did not feel any major power gain. But think about it,  FMF told me on the phone It can add up to 3% to the Hp.  That is almost 1 1/2  Hp on a 250F.  It is very hard to feel a 1 1/2 HP power increase by the seat of your pants.

I called FMF and asked if there is a better map setting I could try. They said they did their testing with the stock mapping. (all zeros;s) So with that said-
I did not expect any massive power gains but I did expect it to be lighter. And lighter it is!  The stock muffler weighed 6.37 lbs. 
The Ti 4.1 RCT slip came in at 4.18 pounds. That is a  2.19 pounds saving!!!!
Bottom line:
I bought this muffler for the weight savings.   Looking at the dyno chart you can see it gains power and looses power thru the RPM.   I did a lot of other weight savings mods on the bike at the same time so I am not sure you can feel the 2 pound savings alone.


Would I buy this muffler again? Yes !!! I recommend this muffler for the weight savings and the cool factor! It looks awesome!  See attached pictures of the Dyno graph  and muffler installed at the bottom of the page below :. :thumbsup:  :ride:

Dyno Graph: http://www.thumperta...-1401219947.jpg

FMF installed on my 2014 YZ 250F: http://www.thumperta...-1401219323.jpg

* * * * *

Good Quality and looks. Noticeable change in the power band but not much of an "Increase"
* * * * *

I bought the slip-on from a known online auction site and just replaced the packing and popped a small dent out. Not bad at all for the price.
* * * * *

Shaved 1 1/2 pounds off from stock muffler.
* * * * -

Great sound, and great power boost
* * * * *

Light weight, single to replace heavy duals

What people are saying about FMF Racing Factory 4.1 RCT Slip-On


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The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.