Slip On Or Full Muffler System (2021 Honda CRF450/250R)

Some muffler questions that get sent to my email inbox usually look like, “which muffler is best for my bike? “Is a full system worth the money or can I just get away with purchasing a slip on”? “Is my stock muffler the best muffler option for me”? Instead of trying to keep answering some of these emails, I thought I would write an article on some of the current 2021 motocross machines and which mufflers do what to the power curve as well as if they are better than stock. Now I haven’t tried every aftermarket muffler out there, but if you’re in the market for one and need to decide on if your bike works best with slip on or full system, you have come to the right place. I have also put together a sidebar on if the stock muffler is worth a crap or maybe you should just save your money because the OEM muffler is a good stock system. Just because it is “stock” doesn’t mean it hasn’t been fully developed by the manufactures. Not all stock mufflers are created equal, so read below and see if you need to keep your stock muffler on your Honda CRF250/450R, get a slip on, or maybe go all out and purchase a full aftermarket muffler system. 

Honda CRF450R: 

Full Muffler Systems Tested: Yoshimura RS-12, FMF 4.1 RCT, Pro Circuit Ti-6.

Yosh Summary: Smoother roll on/less RPM response than stock muffler which makes it slightly easier to control down low. Mid range pulls longer than stock and top end over-rev is as good as stock. 

FMF Summary: Better roll on delivery with a snappier throttle response which can help let the CRF450R roll third gear more through corners. You would think this might be contradictory to what you want out of this machine but this allows to run a higher gear which calms the chassis down. Mid range has a smooth/meaty pull but signs off earlier on top end than the stock system. 

PC Summary: Long linear power character with no real explosive snap down low like the stock system. The PC system calms the Honda’s chassis down under acceleration and adds more mid range, with slightly more top end pulling power. Over-rev is as good as stock. 

Slip Ons Tested: Yoshimura RS-12, FMF 4.1 RCT 

Yosh Summary: Retains more of that smoother roll on power, similar to the full system and keeps the longer than stock mid range power, but to me the rpm response suffered a little on low to mid range areas of the track. I wanted just a little more of that stock muffler excitement in these areas. 

FMF Summary: Throttle response isn’t as good as full FMF system and the Honda will not pull third gear as good out of corners with slip on, but 

Stock Muffler Character: Strong low end pulling power (sometimes too much when rolling corners) with touchy low end rpm response. Broad mid range power with a long top end pulling power. 

Slip On Or Full System?`: The stock muffler is just to touchy down low and that can lead to a lot of mistakes when trying to roll your corners or when you get tired. To me an aftermarket slip on, not a full system is the most bang for the buck on the CRF450R. I prefer the FMF slip on because if it has a snappier rpm response yet a smoother roll on mid range character than stock and this seemed to help the Honda’s chassis the most. The Yosh is also a great choice but maybe slightly too lethargic for my taste on low to mid range rpm response, but I do think t his is a great choice if you’re looking to lighten up your machine as well as tame it down some.  

Honda CRF250R: 

Full Muffler Systems Tested: Yoshimura RS-9, FMF 4.1 RCT, Pro Circuit Ti-6 

Yosh Summary: Less bottom end than stock but more mid range pulling power and top end. Low and mid range rpm response is same as stock with slightly crisper FI feel than stock muffler. 

FMF Summary: More bottom end than stock muffler with increased mid range pulling power, but with less top end pull than stock muffler. Low end rpm response has more snap but muffler is considerably louder than stock. 

PC Summary: Better low end rpm response than stock but with a smoother pulling power out of corners. Mid range pull is longer and allows rider to get into third gear sooner than stock without abusing clutch. 

Slip Ons Tested: Yoshimura RS-9

Yosh Summary: Better low end feeling out of corners than the full Yosh system, but still not as much bottom end than the stock system. Mid range pulling power feels as good as full system but with less top end/over-rev. 

Stock Muffler Character: Smooth roll on delivery with crisp low to mid rpm response. This machine could use more low to mid range torque feel in order to get rider out of soft low speed areas of the track better. 

Slip On Or Full System?: The CRF250R needs more bottom to mid range pull so I have found going to a full system benefits this machine the most. The FMF or PC both have unique characters that I need in order to shift sooner and pull out of corners with more authority. The FMF is a louder muffler system than the PC so if louder mufflers are not your thing you might want to go to the PC system for a deeper/less raspy sound. If you put inserts into the mufflers of the FMF, it kills some of its best benefits (less rpm response/low end feel).  

How To Save Your Subframe On Your 2019-2021 Kawasaki KX450

By: Matt Sirevaag (AKA Vaaaaaaag)

You just took ownership of a new KX450 and you want to change the engine characteristic with a new exhaust. However when listening to Keefer rant on the Pulp MX Show about A-Ray giving away mufflers like he’s Oprah on a Christmas special has you hesitant. You may wonder why the aftermarket exhaust industry didn’t just do as Kawasaki did from the factory and use a rubber grommet to help with vibration and help yield breaking sub frames. Well for whatever reason most exhaust companies mufflers are solid mounted so sometimes consumers are breaking the tabs off the subframes thus mufflers are being laid all over local tracks like toys left on the floor by a three year old.

After breaking  our muffler bracket on our KX450 test bike, we decided to take the stock rubber and mounting hardware to install the new aftermarket FMF exhaust. This is a simple mod that even the most novice mechanic can do at home. Take your aftermarket muffler and stick it in a soft vise or have your wife hold your muffler. Drill/hog out the existing mounting hole with 5/8 drill bit or step bit. Next, install the rubber grommet and hardware from your stock exhaust into your new muffler. Boom! Now you have aftermarket exhaust mounted the way Kawasaki intended it to be. You will get a small amount of float out of the rear section of the muffler, but we have not noticed any unnecessary vibration or slop when riding.

2020 Honda CRF450R Three Way Muffler System Comparison

The 2020 Honda CRF450R is a popular machine. After all of my years with Dirt Rider Magazine as well as doing my own thing over here at Keefer Inc. Testing there has been one thing that hasn't changed… The amount of page views and questions that I get about the Honda are always more than any other color! As a test rider, I like the Honda CRF450R because it’s one of the most difficult bikes to set up for a wide variety of tracks, so that keeps me trying different products and thinking of ways to try and make it better. As a consumer or a local racer, the 2020 Honda CRF450R can drive you nuts at times right? It’s super fun to ride, but sometimes can be a handful at certain types of tracks.

In this article I am going to test the Yoshimura RS-9T, FMF 4.1 RCT, Akrapovic Evolution titanium muffler systems for the 2020 Honda CRF450R and give you some feedback on each one’s engine delivery character. I picked these three muffler systems because they have been one of the best three that I have tried on this particular machine. This isn't a shootout as much as what each system can bring to the table. These three muffler systems have similar characters in some areas of the powerband, but also have enough differences in which you can make a decision based on what type of power you want from your Honda.

Fun Fact: I tested these mufflers on the 2020 Honda CRF450R as well as the 2020 Honda CRF450RWE just to see if the ported head, that the RWE comes with, would change the way each muffler delivered its power. After going back and forth on each machine, the character of each muffler system was the same on the stock cylinder head as it was on the hand ported Works Edition head. The description/results below is accurate for both machines.

FMF 4.1 RCT Muffler System:

The FMF 4.1 muffler system has more bottom end and throttle response than the other two muffler systems in this class. The Honda doesn't necessarily need more bottom end, but the way the FMF system delivers its power can give the rider some added freedom when trying to ride third gear through corners. The bottom end comes on strong and the Honda keeps its exciting, crisp RPM response feeling, but lets you run third gear through corners more than the stock, Yoshimura and Akrapovic muffler systems can. Using second with the FMF system almost makes the Honda a little too much too handle (on roll on) through very tight corners. When going to the FMF 4.1 system I reverted back to map 2 (mellow map) instead of map 1 (standard map) and ran 14/52 gearing. By using map one and going to this gearing ratio, it helped calm the Honda’s chassis down in second gear a little, but still kept its fun natured, snappy engine character. Mid range is broader and pulls farther than the stock muffler, but isn't as good as the Yoshimura system in this area. Up on top end the FMF system almost mimics the Yosh in pulling power feeling on the track with maybe slightly less over-rev than the Yosh system. What I like about the FMF muffler system is that it allows the rider to ride a gear higher in some areas of the track and rewards riders that like to lug their bikes more. The Honda in stock form is not the best lugging machine, but with the FMF system it gives the red bike more of a lazy man’s type of feel by allowing me to use third gear more. The FMF system is louder than the Yoshimura or Akrapovic systems by quite a bit even with the inserts in, but keeps that racey deeper sound. 

The good news is that the muffler packing has lasted longer than I expected. We are over the 12 hour mark on the 4.1’s and they still sound good. I used to get only 8-10 hours on other single FMF muffler systems, but these duals have proved to be more durable. 

Yoshimura RS-9 Muffler System With Works Edition Headpipe: 

Once installed and on the track the Honda’s exhaust note turned from high pitch 250F’esq to a deep throaty more traditional 450 factory race bike sound. The crack of the throttle (or RPM response) is slightly smoother and less crisp than the stock or FMF systems, but to me this is a good thing for the Honda chassis. Rolling out of corners, while in second gear, the Honda feels like it has more traction than the FMF and was more controllable while accelerating out of hard pack corners. The slightly smoother RPM response takes away the Honda’s excitement feel ever so slightly, but helps you gain a little more control coming out of corners. The mid range pull is healthier than stock, but with the Yoshimura system you will not be able to pull third gear through tight corners as well as you can with the FMF system. The Yoshimura system is very controlled and has more mid range torque than any other muffler in this test. Even though the Yoshimura system doesn't have that bottom end throttle response like the FMF system the recovery is still very good. With just the flick of the clutch lever (in third gear) the Honda will be in the meat of the power once again and you will be down the straight in a hurry. I noticed top end and over-rev was as good as stock (which is great), but not as good as the Akrapovic. To me the Yoshimura system is like the YZ450F of the muffler world. It does everything “pretty well” and gives you more rear wheel consistency that the Honda needs. You could tell Yoshimura was focused on smoothing out the bottom to mid-range pulling power when they designed this muffler system and they succeeded in doing so. It is also impressive that they didn’t lose any top end/over-rev in the process and gain a little more control.

The muffler packing that the Yoshimura RS-9 mufflers come with is superb and will last you longer than any other packing in this group. Yoshimura also offers the customer refurbishing, just in case you don’t want to DIY. The stickers on the mufflers themselves also last longer and will not turn color as fast as the others in this group.  

Akrapovic Evolution Muffler System:

Once I swapped to the Akrapovic Evolution muffler system, I could immediately tell this system helped the Honda chassis calm down the most. The Evolution system lets the Honda’s engine roll on smoother at low RPM’s and that smoother feel helps the rear wheel connection as well as provides less pitching (off throttle) than any other system in this test. AKA MORE COMFORT!!! The Honda CRF450R now builds a smoother roll delivery and a pulling power that is longer through the mid range than the FMF or Yoshimura. This type of character can allow you to use second gear in corners more because that second gear hit is not as abrupt or quick, so that doesn't upset your technique or the chassis. The Akrapovic also allows the rider to shift later out of corners and that means second gear is more usable with its increased over-rev capabilities . Pulling power up top is increased slightly as your shifting points can be altered now because of the longer pull in each gear. I ran the 14/52 gearing with this muffler system but decided on going back to the stock 13/49 gearing in order t get some mid range recovery back. The Akrapovic doesn't have the the bottom or mid range throttle response like the FMF or Yoshimura systems so this can give the Honda a slightly heavier feel on tighter tracks. The Honda has so much power to work with that a little less “hit” as well as “recovery” can actually help on faster/flowier tracks, but can also make it slightly heavier feeling than the other two mufflers when moving the Honda side to side. I really like that the Akrapovic system relaxes the engine as well off throttle and provides the CRF450R with less engine braking. This really comes into play on tracks with hard pack chop and small de-cel bumps.

The sound/pitch of the Akrapovic is ridiculously quiet when on the track and will almost give you that MXGP sound and feel. It still has that racey, crisp sound on higher rpm’s, but just not that raspy high pitch tone of the stock muffler. I preferred the quiet inserts left in because it created more back pressure and gave me more traction at the rear wheel (out of corners) in all three engine modes. I was normally a map two guy with the stock muffler, but with the Akrapovic installed I am now a map one guy all day long because of the added rear wheel/friendlier connection. The muffler packing has proved to be durable but the stickers on the mufflers turn color quickly and get blown off.

Overall: I always let people know if you have no problems with your stock muffler system and like the way your Honda runs then by all accounts you can disregard this test. Just because I test something here doesn’t mean you absolutely 100% NEED it! If you’re in the market for a muffler system, have some extra money and want to know which direction to go then study up! If you want to alter or change your Honda’s engine character slightly, this test can help you decide on which direction you want to go. To me all of these systems in this test are better than the stock system because it helps the Honda’s chassis in one way or the other and offer spark arrestor inserts for the off-road guy. The Honda doesn't need more power as much as it needs a broader more forgiving connection to the rear wheel. These systems help the Honda in this area. 

Breaking The Systems Down:

Bottom End: FMF

Mid Range: Yoshimura 

Top End: Akrapovic

Over-Rev: Akrapovic

Low RPM Response: FMF

Mid RPM Response: FMF

Top RPM Response: Yoshimura

Controllability/Connection: Akrapovic

Weight: 

FMF: 8.5 lbs.

Yoshimura: 8.4 lbs.

Akrapovic: 8.4 lbs.

Sound/DB:

FMF: 121.1 DB

Yoshimura: 116.8 DB

Akrapovic: 116.1 DB

Pricing: 

FMF: $1499.99 www.fmfracing.com 

Yoshimura: $1499.99 www.yoshimura-rd.com 

Akrapovic: $1549.99 www.akrapovic.com 

If you have any questions about this test, please feel free to email me at kris@keeferinctesting.com. I am here to help if needed!

FMF Vs. Pro Circuit (2020 Yamaha YZ450F Muffler Comparison)

Yamaha did a great job with the stock muffler and I bet if you ask any aftermarket muffler manufacturer they would tell you the same thing. If you’ve seen my social media pictures while riding the Yamaha YZ450F, you will see that I run the stock system quite a bit. Why? Because it’s really good! However, I know some of you out there will not keep the stock system on your bike because you may want something lighter, more attractive, and hopefully get something with more power than the stock system right? That is why I went to work and really picked apart the FMF and Pro Circuit systems for the bLU cRU machine. I do know that FMF and Pro Circuit have been working really hard on continuing to improve/evolve their systems for the YZ450F and after riding a ton on each, here are some of my findings.    

Pro Circuit Ti-6 Pro Versus Stock: 

Why The Ti-6 Pro? I chose the “pro” because of the smaller insert that it comes with to pass AMA/FIM sound because I have come to find out that the YZ450F loves back pressure and that smaller insert helps with throttle connection. The exhaust note on the Pro Circuit Ti-6 Pro is not near as loud or raspy sounding as the Ti-6 or T6 so that is another reason why I chose the “pro”. The exhaust note on the “pro” is deeper and slightly quieter, which I personally like more. The power delivery is slightly smoother than stock on very low RPM (4000-6000 RPM), but is only noticeable to very sensitive riders. At 10-15% throttle position there is a slightly softer RPM response, which I didn't mind on nasty, dry, choppy tracks in Southern California. If I needed more bottom on softer tracks, I simply ran a more aggressive map and that helped the “pop” I was looking for out of corners. I usually ran the TP 3.0 map with the Pro Circuit system and it made me happy with the amount of smooth roll on power I had. If you’re looking for more excitement down low and out of corners, try the “Exciting Power Character” map. (https://www.keeferinctesting.com/motocross-testing/2019/9/18/2020-yamaha-yz450f-start-upbaseline-settingstipstricks)

The rear wheel definitely feels more connected to my throttle hand and in comparison the PC system has a more seamless power delivery when transitioning to its mid range pull. The mid-range is where I could stand to get a little more power and this is exactly where the PC system delivers. The meat of the Ti-6 Pro’s power while accelerating down the next straight is noticeably better than stock. I am able to use third gear with the PC system (compared to using second gear with the stock muffler) and even though the low RPM response is slightly softer than the stock system, the mid-range RPM response is much more instant. Mid-range rpm response is crisp and makes the Yamaha feel “lighter” when trying to hop over square edge choppy areas of the track when accelerating. 

I talk a lot about using third gear on a 450 and if the bike is able to pull that gear through corners. The stock YZ450F does this very good and I was worried that putting an aftermarket muffler on would hurt this feeling. The PC system only improves this as I noticed that have been able to use lower RPM’s around the track with lower lap times. I like that I feel that I can work the clutch/shifter less with the PC system. 

Top end pulling power is as good as stock, but the PC Ti-6 Pro doesn’t have the over-rev the stock system has. If you learn to short shift the PC more and let that newfound mid range meat pull you around the track you will appreciate the phrase “work smarter, not harder” a lot more. I was impressed how the Pro Circuit Ti-6 Pro delivered as well as spread out its power and to me, made the Yamaha even more fun to ride. If that’s possible? For you weight watchers out there, you will lose around 1.2 pounds from the stock system and the PC Ti-6 Pro Titanium System runs $1,118.21. You can go to procircuit.com to get yours. 

FMF 4.1 Versus Stock:

The FMF 4.1 muffler system has a deeper more throaty sound to it (over stock) and has a louder pitch than the stock muffler system. On the track, the FMF 4.1 (on the YZ450F) makes almost as much bottom end power delivery as the stock system and keeps that peppy/exciting RPM response. The stock system has more pulling power immediately out of corners, but the FMF 4.1 allows for better traction while rolling the throttle on when the track gets slippery. Where the FMF 4.1 system really impressed me was mid range pulling power when exiting corners. The stock system is excellent in this area, but has a heavy mid range rev feel. The FMF makes the YZ450F’s engine feel free-er and gives the rider a snappier yet more powerful mid range pull with less engine braking.  

I stuck with the “TP 3.0” and “Exciting Power Character” maps on the FMF 4.1 system and that let me choose what kind of power delivery I needed at any given time of the day. With those maps and the 4.1 system you can control the power a little more down low and allow the Yamaha to have a more linear feel in second and third gear. The FMF 4.1 system has a larger muffler opening when you un-box it so make sure not to throw away your insert/spark arrestor screen that FMF includes in the box. If you think you want a little more excitement (bottom end) back into your YZ450F, simply install the insert (with the screen) and the Yamaha will get more back pressure and some more connection/bottom end pull/low rpm response, but you will lose a little of that mid range free feel that you gained.  

Up on top end the FMF pulls harder than the stock system, but falls a little short when it comes to the over-rev department. The 4.1 accepts short shifting, so if you’re like me and love to get into third gear as soon as you can, the FMF does accept that third gear shift a little earlier than stock as well. I like that FMF keeps evolving their systems with each passing model year and to me the 2020 system has some added mid range pulling power that the 2019 didn’t. The FMF 4.1 Ti muffler system will save you 1.5 pounds over stock and the cost of the FMF 4.1 titanium system runs $1099.99. You can go to fmfracing.com to get yours.


Pro Circuit Vs. FMF: 

Let me start off by saying that these are two muffler systems (for this model) that will rival or surpass (in spots) the stock system’s performance. That’s not easy to do! Some muffler manufacturers have better performance or have come up with a better setting for certain models and Pro Circuit as well as FMF have done a great job with their 2020 YZ450F system. The Pro Circuit has a little more throttle to rear wheel connection down on low end, but the FMF pulls stronger through the mid range. Up on top end both seem on par with each other and of course both have less over-rev than the stock muffler. I can lug the YZ450F in third gear more with the Pro Circuit muffler, but the FMF has more of a free feeling to it when higher up in the rpm range. These muffler systems are close in comparison to one another and offer the rider a different power curve than stock that is actually beneficial to the Yamaha YZ450F rider. 

Results:

Bottom End Pull: Pro Circuit

Mid-Range Pull:  FMF

Top End Pull:      FMF/Pro Circuit

Over-Rev:   Stock

Bottom End RPM Response: Stock

Mid RPM Response: Pro Circuit

Top End RPM Response: FMF 

Best Looking: FMF

Stock Heat Shield Mounting: FMF, Yes/Pro Circuit, No