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).  

Yoshimura RS-9T Stainless Full System (2020 Honda CRF250R)

The 2020 Honda CRF250R is much better off the bottom end than the 2018-2019 versions, but we wanted to test the latest full stainless Yoshimura RS-9T to see if it helped the stock Honda’s engine character at all. We were specifically looking for a little more RPM response and pulling power because the Honda is still lacking some bottom to mid power when compared to the other competitors in the 250 class, more specifically the blue bike. Seeing as how my son and I have been logging a lot of hours on the machine as of late, I thought why not get a review up fairly quickly to give you the details. 

Installing the new full system took me less than 20 minutes and the instructions were very detailed. All of the parts that came inside the box fit perfectly and no swear words were thrown while installing the Yoshimura exhaust. In my opinion, Yoshimura is one of the highest quality exhaust manufacturers in the industry. I have been a part of a few R&D departments and I can tell you first hand that the quality, fit and finish of a Yoshimura exhaust is impressive. I wanted the stainless full system because it was less expensive ($909.00) and still knocks off almost a pound over the stock system!

Now to the part that everyone wants to know...Does the Yoshimura help the little red screamer? The simple answer is yes, but who likes simple answers? Not us! With the stock system, the Honda pulled nicely from mid-range to the super high rev limiter that the Honda graces us with, but when exiting corners and trying to grunt up obstacles, the engine needed some help. The best way to explain the stock feeling CRF250R is that it’s just missing some meat. By saying that I don’t mean it’s slow, but I felt like I had to shift a little more with the Honda CRF250R. I had to ride a gear lower at times in corners (than other 250F machines), and if I didn’t, it took a bit of clutch feathering and more shifting to get the bike pulling hard again.

As soon as I fired the bike up with the new exhaust it was clearly a bit louder, not obnoxious, but a nice, throaty sound that was deeper and less raspy. I tested the stock system back to back with the Yoshimura system on the same days, so it was cool to see the places on each track where the bike really felt different. The most noticeable place the bike felt better was out of tight inside ruts that exited up faces of jumps. With the stock system I had to slightly slip the clutch all the way up the lip (to be able to clear the jump). When I bolted on the Yoshimura system I could leave it in the same gear and just use the meat of the new found Yoshimura power to pull me up and over those types of jumps. Some areas of the track I had to be in second gear and then scream the bike on the exit of corners with the stock system. With the Yoshimura system I could now be a gear higher at times and use that extra meat to get me out of a loamy berm more efficiently. From mid to top end I didn’t notice any real added power gains, but I also didn’t feel like the top end suffered in order to get the added bottom end snap that I received with the Yosh. I will say that the mid rpm response is slightly crisper when in third gear as well as the recovery in third gear through deep corners. Bolting on the Yoshimura full system will not make your Honda as responsive as a Yamaha YZ250F, but it will get you a little added excitement that you could be looking for. Plus the Yoshimura mufflers look much cooler than the stock ones. 

If you have a 2020 Honda CRF250R and feel like you’d like a bit more bottom-mid range power, I’d definitely look into the RS-9T stainless system. Yoshimura offers three options, the slip on mufflers ($809.00), the full stainless system ($909.00), and the full titanium system ($1499.00). Admittedly none of these are super inexpensive options, but it’s one of the few things in today’s four-stroke world that can provide a true bolt on benefit. 

You can check out yoshimura-rd.com for more of you can contact me at kris@keeferinctesting.com if you have any questions. 

Yoshimura RS-4 SS/AL Full Muffler System For 2019 Kawasaki KX450

By: Dominic Cimino

Any of you that stay up to date with us here at Keefer Inc. are aware that I really enjoy riding the 2019 KX450. Like I really enjoy it. Maybe it is because we have the chassis and suspension dialed in just for me or maybe it’s just because the bike is so damn fun. Either way, I am excited to continue making improvements to this bike in the upcoming months because every time I ride it I feel faster. Next on the chopping block is the motor department and we decided to start with exhaust first. I wanted to test the RS-4 Stainless Steel Yoshimura system because I have had great luck in the past using their systems on other bikes and the guys over there always take great care of us. 

Yoshimura exhaust systems are made from scratch right here in Southern California. Their R&D facility houses everything from the race team shop, dyno/engine rooms, to the space where they lay all of their own carbon fiber. The attention to detail and quality of product is top notch in everything they produce and to give you a little more background on Yosh, you can watch this short clip:

https://www.youtube.com/watch?v=V5J5kltNfvQ

Although it is a couple years old and mainly showcases road racing disciplines, trust me when I say that it all translates equally into motocross. You can sleep peacefully knowing that your investment is going to be worth it. 

The stock exhaust system on the 2019 KX450 is not too bad overall. Beside it looking really bad (that is a no-contest) and weighing a decent amount, it produces a good tone and useable power. I think this exhaust compliments the motor and power delivery well by keeping things linear and quick revving - one of my favorite traits about this bike overall. But on the flip side, the motor does lack some “meat” in the RPM range and the over-rev tends to sign off relatively quickly at the top. Installation of the new Yosh was quick and easy with every single piece fitting in place perfectly. I love when that happens! The stainless/aluminum system that I tested weighed over a pound less than the stocker and comes in at a fair price of $675.78. In roughly ten minutes, the KX looked better instantly with the new system in place, and when I pushed the button to wake her up, she sounded healthier too. I am not a fan of obnoxiously loud exhaust systems so I was happy to listen to the Yosh when cracking the throttle on the stand. Definitely louder than stock, but not deafening. 

Before installing the new Yoshimura system, I did a couple morning motos at Glen Helen to get the best gauge of the stock comparison. The most obvious difference when cruising back onto the track was the tone, as it has a deeper/healthier sound. But when in stride, the exhaust made the KX come to life from the mid range and beyond. The linear power curve stayed true on delivery, but exemplified a more crisp powerful feel when on throttle. I felt the Yoshimura system was able to harness a little more “meat” that I have been searching for and also helped push the bike into the higher revs more efficiently. On the top end, over-rev was increased quite a bit as the KX seemed to pull longer and harder overall. I noticed when charging down Mt. Saint Helen I could hold 2nd gear almost half way down the hill before hitting the limiter. The stock exhaust would sign off way earlier than that in the beginning part of the day. I also realized I stayed in 2nd gear almost all the way around the Glen Helen circuit. This is a testament to the linear power I have been talking about on this 2019 KX450, and the Yoshimura system makes it even better. Where I didn’t notice a substantial improvement was bottom end power delivery. The KX is not a torquey bike in stock trim by any means, but I was expecting to get a little more bark with the new system. This was not the case and I found myself clutching the bike in the soft corners to wake it up in order to get back into the mid range, where I think it excels. 

Overall, the new Yoshimura exhaust system is a great performance improvement to this already great bike. Looks good, sounds good, and runs good - thats what it’s all about, right? Obviously, I am going to set my sights on continuing to improve the power delivery to round out this new KX450. I am happy with the mid/top end feel, so maybe we can experiment with new map settings to get a little more lovin’ down low.  As always, stay tuned for what is next here at Keefer Inc. If you have any questions about the 2019 KX450 please feel free to email me at dominic@keeferinctesting.com.  Or you can head over to Yoshimura-rd.com to see what they offer for your green machine.

Yoshimura RS-9T Full Titanium Sytem For 2019 Honda CRF250R

It’s no secret that the Honda CRF250R is still lacking some bottom to mid range power when compared to the other competitors in the 250 class in 2019. Seeing as how I’ve been logging some hours on this machine as of late, I decided to test the full Yoshimura RS-9T titanium system to see if we can get some added low end power. Installing the new full system took me less than 20 minutes and the instructions were very detailed. All of the parts that came inside the box fit perfectly and no curse words were thrown out in the garage while installing the Yoshimura exhaust.

Now to the part that everyone wants to know. Does the Yoshimura help the 2019 CRF250R? The simple answer is yes, but who likes simple answers? Not me! With the stock system, the Honda pulls nicely from mid top end, but when exiting corners and trying to grunt up obstacles, the engine needed some assistance. The best way I can explain the stock feeling 2019 CRF250R is that it needs help on “recovery" when the rider makes a mistake. “Recovery” basically means how long it takes the engine to recover by getting in the meat of the power again. When you're tired or lazy and miss a shift, this is where the Honda CRF250R gets smoked by the Yamaha YZ250F. I had to ride a gear lower at times in corners (with the stock CRF250R compared to other 2019 250F machines) and if I didn’t, it took a bit of clutch feathering and more coaxing to get the bike pulling hard again. If the track is flowy and fast the stock Honda works great, but when the track is tighter, this engine suffers.

As soon as I fired the bike up with the new exhaust it was clearly a bit louder, not obnoxious, but a nice throaty sound that was deeper. I tested the stock system back to back with the Yoshimura system on consecutive days, so it was interesting to see the places (at each track) where the bike really felt different. 

The most noticeable place the bike felt better was out of tight inside ruts that exited up jump faces. With the stock system I had to slightly slip the clutch all the way up the lip (to be able to clear the jump). When I bolted on the Yoshimura system I could leave it in second gear and just use the meat of the newfound bottom end power to pull me up and over those types of jumps. When I had to be in second gear and scream the bike (with the stock system), I could now be in third gear and use the smoother/stronger part of the power to exit the turn with the Yoshimura muffler system. RPM response was improved as well and this made the Honda feel even lighter when popping out of corners. Connectivity to the rear wheel was improved and even with that extra RPM response I gained with the Yosh system, I received more rear wheel traction. From mid to top end I only noticed a sightly better pulling power down each straight with slightly more over-rev. This part of the muffler wasn't mind blowing, but took me a couple tracks to figure out that there was a little extra “meat” through the mid range (compared to stock). Overall the little Honda just has a little more RPM response, better pulling power through second and third gears, and a small gain when revving the bike out in each gear.   

 This doesn't mean that your new Honda CRF250R (with the Yoshimura exhaust) is going to be a YZ250F killer, but it closes the gap a little. If you have a 2019 Honda CRF250R and feel like you’d like a bit more bottom-mid range power I’d definitely look into the RS-9T system. There are three types of Yoshimura mufflers that you can choose from; a slip on muffler system ($763.15), the full stainless system ($947.36), and the full titanium system ($1463.15). Admittedly none of these are super inexpensive options, but it’s one of the few things in today’s four-stroke world that provides a true bolt on benefit. Besides, if you were looking to save a few bucks, I don't think you would be rocking a new 2019 Honda CRF250R right now anyway. 

Yoshimura RS-9T Titanium Signature Muffler System For The 2019 Honda CRF450R

If there is one 2019 450 motocross machine that I think has the fastest overall engine character, it would have to be the Honda CRF450R. This engine is basically a race engine out of the crate. If you want to get to point A to point B in a quick manner, this Honda is the engine for you. So why on earth would you need more power? To me you wouldn’t need MORE, but maybe you can massage that power and move it around so that the engine delivery is slightly more controllable. This is where the KTM and Yamaha engines are better than the red machine. Both have more controlled power when the track gets rough or slippery. Controlled power is crucial in today’s 450cc world and a good muffler system can give you exactly this, if it’s a good system. Key word here people is “IF” it’s a good system. It is not as simple as reading dyno charts and slapping it on your bike. It requires real world track testing to feel the power character as well. We wanted to install/test a muffler system on our 2019 Honda CRF450R (that we purchased ourselves) to see if we could improve on a power plant that was already pretty damn impressive. We chose the Yoshimura RS-9 full titanium muffler system to try back to back with the stock system to see if it was in fact, what we were looking for.

 When we originally tested the 2017-2018 CRF450R Yoshimura RS-9 system, we thought it was a pretty damn good system that was better than stock. However, the 2019 CRF450R stock exhaust changed for the better, so Yoshimura went to work on a new headpipe design to try and achieve even more power (than the stock 2019 exhaust system). Yoshimura also wanted to tuck in the new headpipe design, so it was less susceptible to crashes.

 Once installed and on the track the Honda’s exhaust note turned from the high pitch semi raspy stock sound 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 that of the stock system, but bottom end pulling power is increased over stock. Rolling out of corners, in second or third gear lets the rear wheel find increased traction over stock and was more controllable while accelerating out of hard pack corners. The slightly smoother RPM response takes away the Honda’s exciting feel slightly, but helps you gain a little more control coming out of corners. This is what I was looking for in a Honda CRF450R muffler! The mid range pull is healthier, with more meat, than stock and while the stock system had a tough time pulling third gear in tight/slower corners (without a gearing change), the Yoshimura system will give you an easier time rolling third gear in those tighter corners. With just the flick of the clutch lever (in third gear) the Honda will be in the meat of the power once again and have you down the straight in a hurry. We noticed top end and over-rev was better than stock, as the Yoshimura system helps the Honda carry second and third gears longer. It pulls amazingly well on deeply tilled dirt in second and third gear and there wasn’t a time where I thought to myself  “I need more top end pulling power”. You could tell Yoshimura was focused on controlling, yet increasing, the bottom to mid-range pulling power when they designed this 2019 CRF450R muffler system and they succeeded in doing so. It’s also impressive that they didn’t lose any top end and over-rev in the process, in fact they got some extra!

Craftsmanship is second to none with the Yoshimura RS-9 titanium mufflers.

After weighing both the stock and Yoshimura RS-9T systems you will be saving almost two full pounds, which is great since the Honda is on the heavier side (on paper) for a 450cc motocross motorcycle. This is a significant weight loss but for $1,499.00 it is a very pricey bolt on modification. If you are looking to save a little money, Yoshimura offers the stainless steel/carbon version for $980.00, but you will not be saving much weight (only half a pound). 

Again you can’t say enough about the craftsmanship that goes into a Yoshimura system. The welds are flawless and the mufflers tuck up inside the side number plates for a stealthy, compact look. If you’re looking for a little added pulling power, with more control/connection on the track, and not to mention sexiness out your new 2019 Honda CRF450R, the Yoshimura RS-9T system will help you do all of those things very well. You will have to decide if you want to dip into your checking account to pay for these added features, but if you're in the market for a 2019 Honda CRF450R muffler, there is not a better system out there for this model. The Yoshimura system has held up great over my years of testing them and you can even send your system back for Yoshimura to re-furbish if you choose (for a fee of course). You can head over to Yoshimura-rd.com to get yours or call them at 800-634-9166.