FMF Factory 4.1 Slip-On Exhaust

FMF Factory 4.1 Slip-On Exhaust
FMF Factory 4.1 Slip-On Exhaust

$359.99 - $449.99
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  • Description
  • 28 Reviews
  • 37 Questions
  • Fitment
Description Item #FMF0003

The FMF Factory 4.1 slip-on exhaust is the same exhaust that professional racers use to bring home championships around the world. FMF constructed the Factory 4.1 slip-on exhaust to offer the lightest weight slip-on on the market. The technology in this slip-on exhaust cannot be found in any other exhaust. The proprietary Chamber Core technology allows for smoother and more efficient exhaust flow to maximize the power output. Since the Factory 4.1 slip-on exhaust is meant to be used for competition, FMF made this pipe ready to take to the track straight out of the box. The FMF Factory 4.1 has been designed to allow for easy maintenance with a removable sleeve for repacking and it offers the ability to fine tune the performance of the exhaust with the addition of tuning inserts and the option of a spark arrestor to give you no boundaries.

  • The lightest system available.
  • Boosts low-mid torque and offers a broader powerband with more over-rev.
  • Patented Chamber Core for optimum performance.
  • Engineered for compactness and centralized mass for improved handling.
  • Exclusive mounting design.
  • Easily serviced for re-packing.
  • Slip-on mufflers are available with a titanium or stainless steel midpipe.
  • Customizable with performance tuning inserts and spark arrestor module.
  • Meets AMA sound requirements on most models.

Note: For closed course competition use only. Not intended for street use.

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28 Reviews
4.6 out of 5 stars
5 Star   26 4 Star   4 3 Star   1 2 Star   1 1 Star   1
Durability   Ease of Installation   Performance   Power   Style  

I got this as a Christmas present, it added plenty of power to my crf 150r and installing it wasn't that hard. If it broke which it hasn't after 2 years, I would defiantly buy it again.

FMF Factory 4.1 Slip-On Exhaust
Verified Purchaser
United States
Durability   Ease of Installation   Performance   Power   Style  

I like the exhaust and power bomb header a lot! The only problem I had with this was installing it. It was a huge pain in the you know what. You have to buy your own clamps to secure the power bomb header to your exhaust. You also need to buy high temp silicone. This costs about $30, and you also have to let it sit for 24 hours for the best outcome. Other than that it took me about 30 minutes to take the old exhaust off and put the new one on. Hope this helps to future customers.

Verified Purchaser
Port Orchard, WA, USA
Durability   Ease of Installation   Performance   Power   Style  
FMF Factory 4.1 Slip-On Exhaust

Love this pipe! Was easy to install, sounds great, and excellent power increase. (I also installed a power bomb)

Miami, FL, USA
Durability   Ease of Installation   Performance   Power   Style  
The best pipe there is

the fmf slip-on exhaust is the best exhaust out there i put it on my raptor 350 and it is amazing.the bike has a noticeable increase in speed horsepower and torque.the pipe has a very deep sound to it without the spark arrester and with the spark arrester it is very quiet.Thank you motorsport team for the great advice of the pipe and evrything else.

mountaintop pa
Ease of Installation   Performance   Power   Style  
07 polaris outlaw 525

I put this pipe on my sons outlaw and it is outstanding. 10 minutes to install and it sounds like a hoard of bees , may be loud for some but I like it Haha neihbors don't but who cares. the power is instantly noyicable.only one pet peeve , when not on the gas it has a peculiar whistle which makes it sound like something is loose and rattling on it.highly recommend if you don't mind loud

Terrell, TX, USA
Durability   Ease of Installation   Performance   Power   Style  

I installed the Factory 4.1 on a very strong running 07 Honda CRF450R and what a huge improvement. Combined with a FMF Mega Bomb header this thing is a beast. installation was a simple 15 minute task, the fit is perfect. Awesome product.

Eugene, OR
Durability   Ease of Installation   Performance   Power   Style  
5 Star Muffler From FMF

If you are looking for an exhaust, this slip on application is a great addition to your bike. I installed it on my 06 YZ450F. Would buy another one in a heart beat if need be. Installation was a breeze with the slip on, the blue anodized finish is TRICK, and the muffler is holding up really well after numerous rides.

RIDER BEWARE!!!!! This is a louder pipe designed for closed course riding. If your riding area is stringent on decibel ratings, think about some of FMF's quieter mufflers such as the new Q4. The new ones look much better than the ones I saw when shopping for mufflers and believe me, they will not get you tickets that end your ride!

This muffler is trick!
Verified Purchaser Featured
Orange County CA
Durability   Ease of Installation   Performance   Power   Style  
Hits Hard!

Paired this up with the Megabomb header. Night and day difference! Hit much faster than stock and noticeable mid range increase. Used this set up on 2011 YZ450F

Verified Purchaser
Durability   Ease of Installation   Performance   Power   Style  

This product combined with the power bomb header completely got rid of the throttle snap bog on my 2007 crf250r. Added tons of power on bottom and mid, would recommend to anyone lookin to get rid of the stock duals

FMF Factory 4.1 Slip-On Exhaust
FMF Factory 4.1 Slip-On Exhaust
rathdrum idaho
Durability   Ease of Installation   Performance   Power   Style  

i had just sold my go kart and used the money i had earned to buy this and the megabomb header...i would say that is not necessarily worth the 600 dollars only because im not a pro rider i am sust starting to race. but it dafinately helped my CRF 150R in the manner of my 2nd gear holeshot, it kickes butt now...

Top 500 Contributor
Peralta, nm
Big Difference

I have been running another brand of pipes on both of my CRF250Rs for just over a year now. I put a power bomb header with a 4.1 muffler on my '09 and WOW what a difference. Not only did it lower the sound, but the power increase was very real from bottom to top.

Southern Illinois
Good, Quality Exhaust

I put this slip on exhaust on my 2005 Yamaha YFZ 450. It went on without any problems. FMF also gave a larger main jet with this exhaust. I contacted FMF and they said the larger jet should keep the air fuel mixture correct but if it is not perfect to turn the air/fuel screw located on the bottom of the carb out a half turn. I put the jet in but did not mess with the air/fuel screw and my atv runs great. There is a big difference with this slip on exhaust and I recommend it to everyone.


Great product...low to mid range gains

east coast NC
Sick pipe.

I just got this pipe and the powerbomb header for my 2012 yfz 450r replacing the corked-up stock pipe, and saw amazing improvments from bottom to top end. all around great product. oh and incase you were wondering like i was, no fuel optimizer is needed.

2012 yfz 450r
Jax Bch, Fla
Nice bang for your buck

Noticeable power increase on my '09 YZF 250 looks and sounds sick. My next purchase will be the megabomb header, to go with it

Elkhart indiana
It goes ham with the mega bomb

I like it it added lots of power I was riding on the road and went to full throttle for a race takeoff and my tires just got to spinning. Very good buy check my bike out on Facebook. scar ray is my name on there

Durability   Ease of Installation   Performance   Power   Style  
Good but has major flaw

Decent exhaust in all categories but in my opinion has a major design flaw when put on a CRF250X.

When trying to lift the bike onto the stand or move the bike around in the back of the truck, there just isn't enough room between the fender and the exhaust to use the traditional grab spot under the rear fender without burning your hand from the much too close exhaust.

It could also be a major problem if you're a woods rider, like me, and ever have to try to lift the rear end out of a mud hole after getting stuck.

I've never encountered this problem on any other bike / exhaust combo I've ever had. The stock Honda muffler doesn't have this problem.

Needless to say, I'm pretty disappointed in my purchase and wish I could return in.

The ZOO, Mi
Durability   Ease of Installation   Performance   Power   Style  
Good pipe

Bought for 06 crf250r, already had the fmf megabomb on bike, fit good the only complaint i have is the tire (stock size) rubs the exhaust when suspension is compressed. makes good power and sound with the 94Db insert

Houston tX,-so. cal
Durability   Ease of Installation   Performance   Power   Style  
Very easy install love the sound

This was easy to install. Noticed power out of the turns right away. I was always a factory replacement guy no aftermarket parts, I'm very happy with this product.

State College, PA
Durability   Ease of Installation   Performance   Power   Style  
Great Buy

easy to install and great power
looks great on my 09 yfz450r
i put this on along with the mega bomb header the pair made the bike feel like a whole new animal

FMF Factory 4.1 Slip-On Exhaust
FMF Factory 4.1 Slip-On Exhaust
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37 Questions
Answered:   37
Not Yet:   0
Location: Sacramento
Q: Does this have a mid pipe, that would directly fit to the fmf powerbomb header?
1 year 5 months ago
Does this have the mid pipe included
Top 1 Contributor
1 year 5 months ago
A: Yes, the FMF Factory 4.1 Slip-On Exhaust comes complete to mount to the header. feel free to give us a call at 888-676-8853 and we would be happy to help you out with your order.
Location: Springville, UT, USA
Q: Old newer dual exhaust fit on older models?
1 year 7 months ago
I have a 2006 crf250r and I was wondering if like the new dual exhaust slip on pipes made for the 2015 model would fit on my 2006? Or any after market dual exhaust pipes for that madder
MotoSport Staff Expert
1 year 7 months ago
A: No, the 2015 CRF250R exhaust will not work on the 2006.
Q: What is the db rating for this exhaust without a spark arrestor or quiet insert?
1 year 9 months ago
Top 1 Contributor
1 year 8 months ago
A: FMF does not have a db rating for the Factory 4.1 Slip-On Exhaust without the insert. FMF rates the insert as a 94db unit. .
Location: Moncks Corner, SC 29461, USA
Q: Would i need to re jet my carb from stock for this pipe and the powerbomb? i bought my bike with this pipe and a little smoke comes out occasionally?
1 year 10 months ago
My 2008 yz450f came with this pipe on it and i recently added a powerbomb head pipe made by FMF and have great power gains. although i got my bike used it was in really good condition! but it puts out a little smoke? i was wondering if it is a jetting issue or oil getting past the rings on the piston. i checked my air/fuel screw and it was at 2 turns out from all the way turned in. ive always heard thats stock specs.. it takes a few kicks to crank but it runs strong!! please help ? does it sound more like it needs a new jet? if so which one and what size should i go with? or is it a piston and ring ? what little bit of smoke i see come out of my pipe looks blue and a friend of mine says it looks like it could be black..
Expert MotoSport Staff
1 year 9 months ago
A: There is not a specific setting I could give you for jetting your bike. It would really depend on your location (altitude/temperature) and how your bike is running with the current jetting. Jetting can be very tricky, there isn't one setting that will work everywhere with every bike. I would recommend taking your bike to a local motorcycle dealership’s service department to have your bike properly jetted.
Location: Helper, UT, USA
Q: I have a FMF mega bomb header andd pipe i want to get the 4.1 factory pipe is there a way i can get just the 2 mufflers? for an 08 CRF250?
2 years 2 months ago
MotoSport Staff Expert
2 years 2 months ago Location: Portland, OR, USA
A: From what I can find, FMF only would make the Factory 4.1 Slip-On in a single sided version for your 2008 Honda CRF250R. (
Location: Washington
Q: Does this slip on include one of these?
2 years 2 months ago
I need the insert that is both a spark Arrestor and a quiet core in one.
Expert MotoSport Staff
2 years 2 months ago Location: Portland, OR, USA
A: This Slip-On would include a removable screen spark arrestor insert but it would not be the Quiet Core Spark Arrestor. You would need to purchase the Quiet Core Spark Arrestor Insert separately from the Slip-On.
Q: I have a 06 crf250r and was wondering if it came as one pipe slip on or the dual system?
2 years 3 months ago
MotoSport Staff Expert
2 years 3 months ago Location: Portland, OR, USA
A: Originally your 2006 Honda CRF250R came with a dual exhaust. This FMF 4.1 Exhaust would be the single slip-on exhaust for your bike. It would include the mid-pipe and muffler to convert your CRF250R to a single exhaust.
Location: australia
Q: Will this fit my standard header pipe?
2 years 4 months ago
i have a 2010 ktm 530exc in australia and was just wondering if this slip on fits the standard header pipe.
Expert MotoSport Staff
2 years 4 months ago Location: Portland, OR, USA
A: Yes, FMF Slip-On exhaust systems are designed to fit OEM headers and FMF Headers. Normally FMF will include a spacer sleeve (if necessary) that fits into the end of the mid-pipe that allows the pipe to mount up to the Stock KTM Header.
Q: Do you have a fmf slip on pipe for a 2005 crf250r?
2 years 4 months ago
MotoSport Staff Expert
2 years 4 months ago Location: Portland, OR, USA
A: Yes, This FMF Factory 4.1 Slip-On would fit your 2005 Honda CRF250R and we also have quite a few others that would fit your bike too. Just be sure to input your bike as the ride you are shopping for and the website will show you what slip-ons would fit your bike. Or here is a link that will get you there directly:;CRF250R;2005&mmy_source=topnav
Q: Do the FMF Factory 4.1 Slip-On Exhuast meet 96 db?
2 years 8 months ago
MotoSport Staff
2 years 8 months ago
A: Currently the AMA has a 94db limit. FMF states that it meets AMA sound requirements on most models so you should be just fine if the tester follows the AMA testing procedure. The AMA will test 250 four-stroke at 5000 rpm and a 450 four-stroke at 4500 rpm.
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