Pro Circuit T-6 Stainless System (2022 Kawasaki KX250)

The muffler on the stock 2022 KX250 sounds a little too blown out for me in stock form (even when new). The tone of the muffler is not pleasant to the ear, so I crossed my fingers, called Pro Circuit and picked up a T-6 (stainless system) Muffler System to see if it enhances the current engine character of the KX250. Ti-6 and Ti-6 Pro systems are tough to get at the moment so we settled on a stainless system, which can last longer (more durable) than a titanium system. While I had a PC system, I thought it would be cool to give you guys a run down on a couple other mufflers that I have tried on the KX250 and compare those with the PC (see below). Here’s what I came away with… 

Immediately I weighed the stock and PC T-6 mufflers and took notice of how the Pro Circuit system cut just over 0.7 pounds off the green machine so we were starting off well. The next thing that made me happy was that the PC muffler goes on easy and literally took me 7 minutes to change out! Boom! So far so good! After installation I recruited my son to help me evaluate the system as he now has a new found love for the KX250 and a Team Green ride that didn’t exist last year. I made him write his notes down and I told him we would compare both of ours after we have tested this muffler at a few different tracks. We tested the T-6 at Glen Helen, Perris, secret dez tracks and State Fair MX just so we knew exactly what we were getting out of the PC system. 

 When you purchase your T-6 muffler it will come with a spark arrester screen already installed inside the muffler. DO NOT REMOVE THIS! This helps with back pressure and gives the KX250 the RPM response and bottom end that Aden (my son) and I both like. When we took it out the PC system lost some excitement down low and lost a little bottom end. You can however punch a small hole through the back of the screen and then reinstall it. Doing this actually helps give the PC system a little more bottom end/RPM response while still retaining that back pressure that is important for rear wheel connection. 

Ok so now that we got the “tricks” out of the way, how does this PC system compare to stock?. Normally I DO NOT get more bottom end with a PC system (versus stock) on any brand of bike, but I was surprised that I got a little extra bottom end pulling power out of the PC system. RPM response is a little softer than the stock system, but when opening up the throttle out of corners the KX250 (with the PC system) pulls harder than the stocker. Mid range is where you will feel the meat of this power. When accelerating out of the corner and shifting to third, the KX250 doesn't have that “empty” feeling that the stock muffler has at times when the track is tilled deep. The PC system keeps pulling once the KX250 is shifted into third gear and continues to pull harder into the top end. Over-rev is as good as stock and I didn’t notice any loss of over-rev when swapping the two mufflers back and forth. 

 The only real negative I have found from the PC system is I wish it would have a little more low end RPM response, like the stock system. The stock muffler has such great initial touch of throttle which can make the bike feel a little lighter when hopping over bumps or popping out of blown out berms. The PC system pulls better out of corners, but is just a smoother initial touch (AKA, low end RPM response). If you want more low end RPM response and could stand to lose some pulling power then take the screen out of the T-6. Doing this will give you more low end RPM response, but will hurt some mid range and it will not sound as good in my opinion.

Overall Aden and I are pleased with the PC system for the 2021 KX250 and I guess we shouldn’t be surprised as they do have that Kawasaki race team and all. My son surprisingly felt most of the pulling power, but didn’t feel much increase anywhere else, so not bad for a 14 year old squirrel. Hey, Mitch! If you’re reading this, good job! Chanceability that he reads this? ZERO. POINT. ZERO! 

Extra Credit: We tried a HGS and FMF system just to see what we had in the Pro Circuit T-6 Muffler System. 

HGS: The HGS has a bottom end feel similar to the Pro Circuit system but not as good as a mid range pull. The HGS system has more top end than the PC and FMF system, but it takes a little work to get there. If I was riding a sand track, I could see how someone could like this system. Great top end-over-rev. 

FMF: The FMF has more bottom end than the PC system and has slightly less mid range than the PC, yet more the than the HGS. Top End is short and over-rev has slightly less. than stock. 

FMF Fatty/Gnarly Pipe & Powercore 2 Silencer (2022 YZ250)

The 2022 Yamaha YZ250 is a hell of a fun bike to ride. Even though I am not a huge two stroke guy, I had a great time riding it and thought it had a better engine character than the previous model. The new intake design really helps smooth the power down low and makes it broader through the mid range. There is more rear wheel connection than I remember on the 22, which makes four stroke lovers appreciate this two stroke. I had the chance to try an FMF Factory Fatty pipe as well as a Gnarly pipe with a Powercore 2 silencer and wanted to give you some feedback to see if it could be worth your while on your new 22 Yamaha YZ250.

FMF Factory Pipe/Powercore 2 Silencer:

After installing the FMF Factory Fatty Pipe and Powercore 2 there was some noticeable changes to the YZ’s power character. Bottom end had a cleaner feeling down low as the stock YZ250 does feel slightly rich on low rpm situations. As soon as you crack the throttle you will get a cleaner response, but not any added snap down low. Where you feel the Factory Fatty pipe/Powercore 2 combo is through the mid range as the YZ250 has better pulling power when shifting from second to third out of corners. I also had the feeling that the YZ250 now had a longer pulling top end/over-rev feel and could pull 2nd, 3rd and 4h gears longer down straights than the stock system could. When the track is deeply tilled the FMF system does make the YZ250 feel a little more spunky with its clean mid range rpm response so popping out of corners in a hurry is made easier. I did notice slightly less rear wheel traction with the FMF system, but I don’t think people that are looking to purchase a two stroke pipe and silencer aren’t necessarily looking for rear wheel traction. Overall, the FMF Factory Fatty pipe and Powercore 2 silencer is a nice upgrade from the stock system. Not to mention that it looks really nice with that raw pipe against that blue plastic. 

Gnarly Pipe/Powercore 2 Silencer:

If you’re looking for more bottom end hit, lugability as well as more rear wheel traction the Gnarly pipe/Powercore 2 combo is your ticket. This combo will help with bottom end rpm response and keep that clean feel that the Fatty has, but will get you more snap as well as allow you to lug the YZ250 a little more through corners. If you find yourself a gear too high at times through corners the Gnarly has better recovery than the Fatty does. As weird as it sounds this combo gave the YZ250 more rear wheel traction/feel than the stock system or Fatty/Powercore 2. I can roll the throttle on sooner with this set up and not break the rear wheel loose as easy. Mid range meat/pull is slightly better than stock, but not as good as the fatty. The down side to the Gnarly pip/Powercore 2 silencer is that it made the top end feel rich/dirty so I had to lean the clip (raise one) as well as go down one main jet size. Once I did this it helped clean it up but still didn’t pull as good on top as the Fatty did. 

If you have any questions about this test please feel free to email me at kris@keeferinctesting.com.

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).  

FMF 4.1 RCT Muffler System (2020-2021 Honda CRF250R)

The 2020-2021 Honda CRF250R chassis is one of the most fun to ride in the 250 class, with its easy to corner nature as well as a great suspension package. However, Honda focused a lot of their engine R&D on peak horsepower and not torque, which to me the CRF250R lacks the most of. When riding the Honda back to back with other models in its class, it’s obvious that the Honda needs a little help/pulling power out of corners. I went to FMF to see if they had what I needed in a muffler package and came away with these thoughts for you to digest. 

Let’s address the elephant in the room first. Can I even get one at this time? Sadly, most likely not. COVID has done a number on a bunch of stock with anything related to dirt bikes! This is not just with FMF, Pro Circuit, Yoshimura, etc., as this is happening with a lot of other key parts to our industry as well. The reasons go from not enough workers/employees to keep up with the demand to not enough material to build the product. This pandemic affects eery business and our industry is no different. This is a good thing and bad thing. Our industry seems to be booming, which is great, but us die hard moto dudes have to wait for months to get a damn muffler! That sucks and I get, but you need to breathe! FMF plans to have Honda mufflers back in stock in March, so if you have placed an order for one of these or any other Honda FMF muffler system for that matter, look towards the middle of March for delivery. Give these muffler companies some time and patience as we all are dealing with some sort of back log because of the pandemic. Plus I have heard that some people just simply don’t want to work at this time!

I like the fact that even though there are two headpipes and two mufflers it still didn’t take that long to install. The headpipes go on super easy and the mufflers slide into the slip fit joints with ease, yet are tight enough so the joints don’t wear out too soon. I have over 20 hours on the FMF 4.1 RCT mufflers and the slip fit joints are great, which is rare for titanium slip fit joints. Another added feature is that you will be losing close to two pounds off of your CRF250, which can also aid in helping the Honda’s chassis even more.

So let’s start off with a couple things I didn’t like from the FMF 4.1 RCT system. The pitch/sound of the FMF 4.1 RCT mufflers are LOUD! The sound is deep and throaty but it is loud compared to other aftermarket mufflers! I didn’t run the quiet inserts, but I plan on trying these to see what it does to power and sound. Once I rode with the system for an hour or so the sound actually improved/dampened as the packing inside expanded. So don’t completely freak out when you first start it up. The second thing that you must pay attention to is that the headpipe springs can break and that could cause your headpipes to pop away from the exhaust ports of the cylinder head. I had this happen two times over the course of almost 22 hours so make sure you keep new springs on the headpipes. I learned if you keep new springs on, the headpipes remain on and don’t give you any issues. I would go no more than 8-10 hours on a set of pipe springs. 

Now with everything I did like about this muffler system: The power delivery is great and FMF made more power where the CRF250R needed it! The Honda needs bottom end and this is the only dual muffler system that has given me more grunt/low end out of corners! THANK YOU! The Honda CRF250R comes out of ruts/deep soil stronger and pulls harder through the mid range. Second and third gear recovery is improved as well as low-mid RPM response. The FMF 4.1 RCT muffler system makes the Honda feel more exciting and lighter around the track, which helped me improve my cornering. Top end/over-rev is as good as the stock mufflers and to me that is just fine because now I am able to short shift the CRF250R more than I could with the stock system. I am running a 13/49 gearing spec with the FMF 4.1 RCT system and that gives me more options with third gear through corners. With the stock muffler and 13/48 gearing, using third gear wasn’t even a thought in my head.

The FMF system will set you back $1500.00 which is my last gripe of this article! Holy crap that is expensive, but at least I know if I have my mind made up on spending my money on an aftermarket muffler system, I know I am getting something out of it with the power increase.  You can visit rockymountainatvmc.com or fmfracing.com to get yourself on the list for the next production run. 

2020 FMF Factory RCT 4.1 Stainless Full System (Suzuki RM-Z450)

FMF has helped us on many builds and you may be wondering why do we use them so much? Well… A couple reasons are because FMF is a great American made company, they are easily accessible to us dumb media people and they actually care about the results of their product. If for whatever reason they missed the mark on a muffler setting they are willing to make changes asap to make their product even better. There are only a few companies that are easy to work within this business and FMF is one of those. 

Suzuki hasn't won a shootout or for that matter won any professional races in quite sometime, but that doesn't mean it can’t be a great bike for the motocross enthusiast. One of my photographers/test riders Dallas Dunn purchased a RM-Z450 because this is what he could afford and he wanted to ride a dirt bike. Suzuki is selling their machines at a much cheaper price than other manufacturers and that is important to the growth of our sport. We need companies like Suzuki to stick around and help this sport grow. With that being said I wanted to try and get the heavy monstrosity that is the RM-Z450 muffler system off and get an FMF 4.1 system on in order to get you guys some feedback on what it can do to the RMaRMY’s power character. 

First thing’s first. We picked stainless steel because it costs less and is more durable than a titanium slip fit joint. The titanium joints are known to wear out a little faster and you’re not going to save a crap ton of weight going to titanium. If you’re the type of rider that wants lightweight and looks then titanium is your jam, but if you’re looking to just lose some weight over stock and get some durability there is nothing “not cool” about stainless. Speaking of weight the stainless FMF 4.1 system weighs in at 6 pounds 11 ounces which is almost a three pound weight loss from the stock piece. WOW! Bolting on the FMF 4.1 system is simple and takes almost not time at all. 

On the track the FMF’s muffler pitch has a deeper more throaty pitch to it and sounds clean (with stock or lean couplers installed). We will say that you will not get a noticeable amount of more bottom end with the FMF 4.1 system installed, but what you will get is a cleaner, more linear, longer pulling power than the stock system. Out of corners you will feel more connection to the rear wheel and an overall lighter revving feel. It’s tough to find more connection when getting a lighter revving feel, but for whatever reason this is how the Suzuki’s engine and FMF system blend itself together. Pulling second and third gears longer is made easier with the FMF installed, so if you want to be slightly lazier with your shifting after the corner (leave it in second gear longer), the FMF system can provide that for you. One thing you will not be getting is more third gear recovery, so if you’re looking to lug the RM-Z450 more with the FMF 4.1, it will not magically give you a ton more pick up in third gear. That area of the power remains similar to the stock muffler character. The over-rev of the 4.1 is noticeably better with the standard coupler, but if you’re using the white (lean) coupler you may want to give the stock coupler a try again to gain even more over-rev from the stock system. For $749.99 the FMF 4.1 stainless system is a good upgrade from your heavy, slightly lethargic feeling stock muffler engine delivery. Visit fmfracing.com to get yours or you can go to keeferinctesting.com and click on the RMATVMC banner to take you to their website to purchase. 

Weights:

Stock System 9.07 oz

FMF 4.1 Stainless System 6.11 oz

FMF 4.1 Full System Vs. Akrapovic Evolution Full System Vs. Akrapovic Slip On

We recently received the 2020.5 KTM 450 SX-F Factory Edition and after dissecting it for a few weeks, we thought we would test a couple different muffler systems on it. We wanted to see if we could improve upon the KTM Factory Edition’s delivery. The KTM comes with an Akrapovic slip on we thought since we have never tried one of their full systems, we would give that a go as well as an FMF 4.1 RCT full system to see how each compares to the standard Factory Edition set up. Just in case you were wondering, we also compared each muffler to one other and give you a breakdown of each category below. 

FMF 4.1 RCT Full System ($1049.00):

With the FMF system installed you will not be getting increased bottom end pull on the KTM, but you will be getting a little more bottom and mid-range RPM response (or throttle crack for you newbies). I noticed the added RPM response more out of corners (versus the Akrapovic) and the FMF system makes the KTM engine character slightly more free-feeling and exciting. I also appreciate that I am not getting any added de-cel popping (or lean sensation) with the FMF system. The KTM ran just as clean with the FMF system on then it did with the stock muffler. Where you will notice the most improvement with the FMF system is through the mid-range. The mid-range “meat” you will get out of the FMF 4.1 system is downright impressive. Rolling the throttle on out of corners and accelerating you will notice an increased pulling power that wasn't there with the stock muffler. 

Whether you're coming out of a corner in second or third gear, you will notice some extra torque feel getting to the next obstacle. With the added mid-range meat of the FMF system it really helped some of the gearing issues I had on tighter, less flowy tracks I tested at. Gaining some mid-range let me use third gear in some corners that I wasn’t able to with the stock system. With the stock system I would roll into these corners in second gear and have the right amount of "pop" to get me out quick, but I had to shift early once exited, to keep the rear wheel from spinning. Third gear was too tall of a gear to get me out of the corner quick, but provided less wheel spin on the exit. It was always a struggle for me to decide on which gear to use when being pressured from behind, by another rider. 

With the FMF installed I could easily use third gear and have enough "pop" to get me out of the corner in a hurry, yet it kept the wheel spin to a minimum by being able to use a taller gear. The FMF’s 4.1 system made me think less and twist the throttle harder, something I like doing. I didn't get any more top-end with the FMF installed, yet it didn't take any away from the orange machine. I did notice slightly less over-rev with the FMF system (from stock) when I got lazy.

Akrapovic Evolution Full Muffler System ($1299.99):

The Akrapovic Evolution full muffler system has a similar character to the slip on version that comes with the Factory Edition, but with added bottom end roll on and mid range. If you’re expecting a ton of added RPM response (excitement) from your full system compared to your standard slip on, you will be disappointed. You simply will not be getting that much added rpm response with the Akrapovic full system. Instead of a smooth roll on that the FE comes with it now has a little more pulling power in second and third gears and pulls those gears much longer.

Mid range pulling power is increased and the muffler pitch is so quiet you never really feel like you’re “on the gas”. The mid range pull is much more linear and longer than the standard slip on and being able to shift a little earlier with the full system makes it easier to ride in softer conditions. I had a hard time with the KTM 450 SX-F Factory Edition at softer tracks not recovering, if I shifted early out of a corner. With the full system at the same track I was able to shift into third and not have to worry about covering the clutch as much. 

Top end and over-rev is where this Akrapovic Evolution system shines. Adding top end and over-rev to the already very capable Factory Edition only makes this machine more fun to ride. Again, I can’t stress on how deceiving this system is because of it’s quiet nature. I really had to focus in and feel how quick I was going from point A to point B on the track because the pitch of the muffler never sounds “racey”. However even with its quiet note, the Akrapovic full system lets the KTM pull so much farther that it almost feels like a swapped to an aftermarket ignition. The connection to the rear wheel with the full system is unmatched and even though it may seem like it’s not very responsive, the KTM with the Akrapovic full system allows the rider to get on the gas sooner through corners.

If you’re reading this and wondering why you can’t simply purchase an Akrapovic headpipe for your Akrapovic slip on, the answer is they will not mate up. The Akrapovic slip on has a smaller diameter OD, (where it meets the stock headpipe), so purchasing just the headpipe will not work.

Akrapovic Vs. FMF:

Below are your typical engine categories and which muffler is best in what area. 

Bottom End: FMF

Mid-Range: FMF

Top End: Akrapovic

Over-Rev: Akrapovic 

RPM Response: FMF

Rear Wheel Connection: Akrapovic

Weight: (Akrapovic 6.2 lbs.) (FMF 6.9 lbs.) (Standard FE 8.1 lbs.)

Which One Should You Purchase?

If you’re looking for more bottom end excitement or rpm response look towards the FMF system. If you’re looking for the lightest muffler available and want more top end/over-rev you will love the Akrapovic. Cost is also a factor to me, so if I am looking at the most bang for my buck, the FMF is less money and I’m getting a good performance gain compared to the standard Akrapovic slip on that comes on the FE. The FMF muffler stands up to more abuse as the Akrapovic can look hammered quicker. That being said I was super impressed with the connection that the Akrapovic had on dry/slick tracks, so depending on what conditions you ride could be a factor in your purchasing decision as well.

Yamaha YZ125 Pipe/Silencer Comparison (Pro Circuit Vs. FMF)

For over 10 years the YZ125 engine has remained the same. At one time it was the best 125cc engine around, but in recent years that award has gone to KTM/Husqvarna. KTM and Husqvarna’s latest 125cc engines have a wider powerband and is simply more exciting everywhere on the track. Compared to the KTM and Husqvarna the YZ125 lacks bottom to midrange. The rider has to fan the clutch more to remain in the meat of the power curve, which can make a rider more tired in race conditions. I know it’s a 125, but compared to the other two models, it’s just more work. However, once I put my 14 year old son on the YZ125 he mysteriously had faster lap times compared to his KTM 125 SX. How can this be? The reason is “I think” he can corner better because of the KYB suspension and the fact that the YZ125 isn't that “barky” off the bottom end helps him carry more speed. At least this is my theory. This is his first year on 125’s and he doesn't need a rocket ship quite yet because his arms look like spaghetti strings and his legs remind me of a long bird. There’s just not a lot there yet! He’s all D&R! 

To allow him to compete with the other kids his age on the other two colors, he does need a little bit more down low, in order to get out of the gate better. One of the best performance upgrades you can buy for a YZ125 is a good-performing aftermarket pipe/silencer. Exhaust pipes are relatively inexpensive and they do not directly affect the durability of the machine. I tested the FMF Factory Fatty Pipe/Shorty silencer as well as the Pro Circuit Works Pipe/R-304 Silencer combos to see how they compared to one another. I then let Aden chime in on what he feels was better for him. Editors Note: (Aden’s opinion was given to me before this article was written)

FMF Factory Fatty/Shorty Silencer (Kris’s Breakdown): The FMF pipe/silencer combo adds a little more pulling power out of corners over stock, while the mid range on the FMF pulls slightly longer than stock and climbs farther through the top end. The FMF set up doesn't provide more over-rev over stock, but you will notice a healthier second and third gear pull down the straights. The YZ125 runs much cleaner with the FMF pipe/silencer (compared to stock) and looks stealthy as the silencer is hidden behind the number plate. I like that the FMF pipe comes with o-rings already installed and is ready to put on. The faster the track, the more this combination shined.  

Pro Circuit Works Pipe/R-304 Silencer (Kris’s Breakdown): The Pro Circuit Works Pipe and R-304 silencer has a deeper sound than the FMF/stock system and gives the YZ125 more bottom end than the FMF. The PC pipe/silencer has increased pulling power out of corners (mid-range) and just feels like it’s more torquey. When rolling the throttle on you’re able just to feel more meat as you’re able to shift the YZ125 a little sooner. The top end signs off a little earlier than the FMF, but the Pro Circuit allows the rider to have more freedom with his/her riding without having to cover the clutch as much. 

Aden’s Opinion: “In my opinion I think that the the Pro Circuit pipe works better for me because it’s more aggressive coming out of corners than the FMF pipe. Do not get me wrong, the FMF pipe is a really good pipe & silencer, but I like the Pro circuit pipe, because it fits my riding style better. For example, my dad tells me I’m more of a 4 stroke kinda guy, I guess because I lug the bike a lot and the Pro circuit pipe has more bottom end, when I fan the clutch coming out of corners. In my dad’s world he calls that “recovery time”, I know this because I hear him say it all the time on the phone. The FMF pipe & silencer takes a little longer for the aggressiveness to hit when I am coming out of corners. Both pipes are better than the ugly looking stock stuff, but to me I prefer the Pro Circuit by a nose”. -Aden Keefer 

Conclusion: Both companies provide a better product than stock. I did raise the needle clip up to the second position (from third) before we started testing and that proved to be the best overall jetting from sea level to 3500ft. We think both companies have a purpose and have areas where their the strongest. If you are riding GP’s or faster type of tracks the FMF system works well because it allows the YZ125 to pull longer on top end. If you are riding tighter tracks or have a child coming off of an 85, the Pro Circuit system could help give him/her more recovery time when they make mistakes (and they will make mistakes).

If you have any questions about this test, feel free to email me at kris@keeferinctesting.com.

FMF 4.1 RCT Stainless Muffler System For 2020 YZ250F

Written/Tested By: Michael Allen

It’s no secret that the YZ250F is one of, if not the best 250F in the class for 2020. One of the things that makes the YZ stand out is the raw amount of torque it produces compared to the other bikes in the class. Some of the other bikes may put out comparable peak horsepower numbers, but when it comes to useable bottom end torque no one comes close. After the 20-hour mark we started to really notice the stock exhaust getting a raspy, hollow sound that was getting on our nerves, so we called FMF and ordered up their Factory 4.1 RCT Stainless full system with carbon end-cap. The 4.1 stainless system has a great look with the carbon cap and has a weight savings of just north of one pound over the stock system. We went with a stainless system for the durability of stainless over titanium. Stainless slip fit joints last longer than titanium and therefore will not get as loose over time.

Installing the system was very straight forward and easy, as well as fit and finish being top notch. Something I really like about the FMF system is that you are still able to use the stock muffler heat shield on the left side of the bike. I can’t tell you how many Yamaha’s I have melted pants on when the left side of the bike doesn’t have a heat shield. Unlike the stock systems raspy sound, the FMF has a deeper tone that is throatier and far less annoying. Another plus of the 4.1 system is that it comes with a spark arrestor, which not only makes the bike legal to ride in places (that require spark arrestors), but it also helps quiet the bike down even more and even helps shape power delivery (more on that later).

The first time I took the bike to the track with the new exhaust I left out the spark arrestor and I noticed a slightly freer feeling from the engine (note: I was using the “Keefer free feeling” map found here https://www.keeferinctesting.com/motocross-testing/2019/7/22/2020-yamaha-yz250f-on-track-facts-and-figures). This is due to the FMF muffler core being larger in diameter and having less back pressure than stock. This slightly took away from the torquey bottom end as well as a little of the mid range RPM response, but pulled a little further into the top end. After riding the bike for a while with the exhaust wide open, I decided to give the spark arrestor a try after talking to Kris. He explained that some bikes need more back pressure to make the engine preform at its best. Just like he said, after putting the spark arrestor/insert inside, it gave the Yamaha some more back pressure, which really helped the bottom end power out of corners. The bottom end pull was slightly better than stock and the mid range pull was slightly longer, but I felt that the over-rev went back to being as good as the stock exhaust. In my opinion the OEM’s have been very good at perfecting the stock exhaust systems as of late and it has made it harder for companies to make giant gains over the entire RPM range of the stock equipment. That being said FMF has done a great job squeezing every bit of power out of the 4.1 system. Having the removable spark arrestor makes it nice to not only be trail legal, but it gives you the option of creating slightly more torque (insert in) or slightly more over-rev power (insert out). FMF also works with Kris on settings as they will send some pieces for him to try to see what his feedback is. If you know Keefer, then you know he doesn't give a shit about a dyno chart, he wants real world “on track” testing and FMF has been doing this.   

I have been running the 4.1 system for over 10 hours and it isn’t showing any signs of getting louder or raspy. For my personal preference I have been keeping the spark arrestor in because I prefer slightly more torque on my 250F’s. The insert is easy to take in and out using a pick or small screw driver and removing or installing the spiral snap ring. The only physical signs of wear the system has shown is the sticker on the end cap has started to melt and bubble. From my experience this is normal after multiple hours of being ridden hard, but you can purchase new stickers from FMF. It’s also to be noted that keeping your muffler packed with quality muffler packing is key to its performance on the track. We go as long as 20 hours on FMF muffler packing, but will not go much more than that because of performance loss. FMF doesn't have a re-furbing center, so doing it yourself is your only option. 

We will be putting this system up against the competitors soon in a small exhaust shootout so be on the lookout for that. If you have any questions about the FMF 4.1 on the Yamaha YZ250F, please email me at Michael@keeferinctesting.com and I can try to help out as much as I can. 

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

FMF Factory Fatty Pipe/Shorty Silencer (2020 KTM 125SX)

Since the delivery of our KTM 125 SX, my son Aden has been riding it non stop. He also has been barking in my ear about getting a pipe and silencer so it “sounds cool”. While I am usually reluctant to add parts to my kid’s bike for the sake of just doing it, I thought this could be a good way to test a pipe and silencer to see if it actually helps the Austrian two stroke power plant. After I discussed “the conditions” to my kid, I called upon Lil D and the boys at FMF to send me a Factory Fatty pipe and Shorty silencer to try. 

What were Aden’s “conditions”? The conditions were that he had to install the FMF products and help me write this test. I took it upon myself to ride the 2020 KTM 125 SX in stock form as well as with the FMF Factory Fatty/Shorty combo at couple tracks. The installation was fairly painless for my 13 year old. He learned how to use a spring puller for the first time as well as how to push the rubber grommets through the silencer mounting points without stabbing himself with a flat blade screwdriver. Once he got the FMF pipe/silencer installed he of course had to start his bike and see how it sounded and I will have to admit, it sounds pretty bad ass. The pitch of the KTM 125 SX with the FMF pipe/silencer is more of a crisp/barking sound rather than a richer/raspy sound that the stock pipe/silencer comes with. Ok, now that we smoked out the garage and pissed mom off, we loaded up the bike and went riding! 

I went back and forth with the stock set up as well as the FMF a couple times at a few different tracks and I will say that the FMF Factory Fatty pipe/Shorty silencer combo did help throttle response as well as low end grunt. Coming out of corners (with the FMF Fatty/Shorty) the KTM 125 SX has a little more acceleration pull on corner exits and could be shifted a little earlier without falling off. The mid range pull was also longer and overall crispness of the mid range seemed improved. The FMF Fatty/Shorty seemed to lean out the bottom to mid range (in a good way) and made the KTM feel more playful around the track. RPM response was improved throughout the power and the throttle felt more connected to the rear wheel. 

The top end pulling power/over-rev was slightly shorter than the stock set up so I wanted to play with jetting to see if I could get some of that back. I went back and forth on a few different main jets as well as needle jets, but came back to this set up below: 

Jetting Specs:

Needle position: 3rd position from top

Jet needle: 6BFY43‑71 

Main Jet: 520 (500 Stock)

Idling Jet: 35 

Choke nozzle: 80

Needle Jet: S‑7

Idle Air Adjusting Screw: 1.5 turns out/open

With this jetting the KTM 125 SX pulled longer up top and gave Aden/I more over-rev in 2nd-3rd gears. To me these two gears are the most important for Aden as he learns how to improve his corner speed as well as technique. Sometimes Aden will leave it in second or third gear too long (instead of shifting) and having this jetting allows the KTM 125 SX to pull a little longer. This jetting was good for sea level up to 3500ft. Anything higher than 3500 feet elevation and I would go back up to the 2nd needle position. 

Overall, there is some performance gains to be had with the FMF Factory Fatty/Shorty Silencer. Aden has put over 14 hours on the system and the silencer still sounds good and not blown out. He did manage to put a small ding in the bottom of his pipe and that made him mad, but he’s ok with it after he took some WD-40 and Scotch Brite to the thing! Proud dad moment! The Fatty is $249.99 and the Shorty costs $134.99. A lot les expensive than a four-stroke system! 

Below is Aden’s opinion of the FMF and stock pipe/silencer. I wanted to let him have free range on what to talk about, so he can try to get better at communicating his thoughts into a testing format. During the course of this test I never shared my thoughts about the FMF Fatty/Shorty for confidential purposes. His opinion is unedited, but I did clean up a few grammatical errors for the sake of reading. After reading his opinion, I couldn't help but write down my thoughts about his opinion. It seemed too good not to share with you all. Enjoy! 

Aden Keefer Opinion: 

The differences between the stock pipe vs the FMF Fatty/Shorty pipe is that the FMF pipe hits stronger coming out of corners, but on the other hand the stock pipe is a little bit more linear coming out of corners. The stock pipe takes a while for the power to kick in which was ok on hard pack desert tracks that I rode. I did like the FMF pipe more because it was aggressive and you can put the bike anywhere knowing that it’s gonna have the little extra power. The one reason I do like the stock pipe is that since it’s more of a longer silencer I can control it better when I get tired because it’s not so aggressive. Don't get me wrong though! I think the FMF pipe and silencer is one of the best pipes out there. Not does it only make your KTM 125 SX faster, it makes it look super cool and it sounds way better than the stock pipe. I also noticed when we put VP C12 in the stock pipe/silencer it made it run aggressive, but when we also tried out VP C12 with the FMF pipe/silencer it ran like a race bike. It made it so fast that I was pulling all the 450’s going up Mt.St.Helens at Glen Helen. I also think cleaning the FMF pipe/silencer is rewarding. My dad loves to vacuum because he said he can see his progress with his work. I like cleaning my FMF pipe and silencer because I can see my progress as I scrub it with an SOS pad. So to wrap this up, I think that the FMF pipe and silencer is the best pipe out there for any 125's out there.

Dad’s Thoughts About Aden’s Opinion: 

-I appreciate some of these testing comments and at least it shows that he is listening to me a little. So you’re saying there’s a chance! Hallelujah!  

-I like that he could feel that the FMF Fatty/Shorty had more bottom end. That shows me that any kid could install this product and feel the difference. 

-It’s funny that he recognizes how the KTM works on different terrain and can appreciate a smoother power at times. I am glad he’s not a balls out rider! Safety first!

-Pulling 450’s up MT. Saint Helens? Eaaaaaaasy there tiger!

-Of course when I was his age I also thought something that was aftermarket was way cooler! Why? Because it wasn't stock! Duh! After reading his opinion it seems that he’s into the styling of the “Raw Fatty look”. Me too, Aden, me too! 

-Here we go with the C12 talk again! That is all this kid was talking about for a few weeks! “Dad, let’s get some C-12”! “Dad, let’s get some C-12”! I broke down and got some. The C12 did make the KTM’s pulling power stronger, but also leaned it out enough to warrant the jetting change. However, the jetting change that worked with the VP C-12 also worked with pump gas too. Don’t be scared to run that jetting with either fuel. Aden wanted it because of the smell! Mom’s still mad because her kitchen smells of C12 and Maxima Formula K2. Sorry, babe! Not really, because our house smells like a race shop now! :)

-Aden coming in hot with the vacuum reference! Wow! My secret is out now. Great!

-Good job Aden. We have some work to do, but good job son! Love, Dad!      

FMF 4.1 RCT Muffler With SX Style Megabomb Headpipe (2020 KX450)

The Kawasaki KX450 was the most improved 450 machine of 2019 and with Kawasaki not changing anything on the 2020 KX450, I wanted to test some new aftermarket parts to see if I could improve on what I already knew from last year’s machine. I knew FMF had two headpipes available for the KX450, but until recently I wasn't able to try it. The SX Style headpipe comes down like a “lowboy” headpipe and increases the length in order to shift the power character around. So what exactly did the “SX Style” headpipe do to the KX450 and how is it compared to the MX Style headpipe? First let us tell you about the stock KX450’s power character. 

The stock power curve of the 2020 KX450 engine has a snappy throttle response from 0-10% throttle opening (with a free feel to it) and at times can almost be too touchy through corners with the standard green coupler installed. Once rolling on the throttle and passed the corner, the power is not quite as strong as the Honda or Yamaha, but still creates an easy to ride power feel on the track. I didn't necessarily need more rpm response with the 2019 KX450, but I would be lying if I said I couldn't use more bottom and mid range puling power when coming out of corners. If you go back and read my review of the MX Style FMF Megabomb headpipe with 4.1 muffler from 2019 (https://www.keeferinctesting.com/offroad-testing/2018/8/14/fmf-41-rct-titanium-muffler-system-2019-kawasaki-kx450) you will read that the MX Style Megabomb smoothed out the low end power delivery more than the stock muffler system did, but had more mid range meat, which was noticeable immediately. In a perfect world, I would love to get more of that newfound mid-range “meat” (that the MX Style and FMF 4.1muffler system brings) and shift some of it towards the bottom end. This is why my curiosity lead me to this FMF “SX Style” headpipe.  

As far as bolting on the complete system, it really is a painless install. The 2020 Kawasaki is the lightest Japanese bike in stock form, but when FMF sent me the full titanium system, I was surprised it dropped the Kawasaki’s weight by 2.4 pounds! Also this is just my opinion, but the titanium FMF 4.1 system is one of the most stunning aftermarket mufflers you can put on any bike. I love the blue anodized finish against the green plastic and it makes the whole bike pop more!

Comparing The FMF SX Style Headpipe To The MX Style FMF Megabomb Headpipe:

So how do the two headpipes with the FMF 4.1 RCT muffler compare to each other on the track? The SX Style headpipe, along with the 4.1 RCT muffler made the KX450 feel more playful out of corners than the MX style megabomb that I tried on the 2019. The low end RPM response (0-10% throttle opening) was slightly less with the SX Style headpipe (without the muffler insert), but now the KX450 had slightly more bottom end pulling power without sacrificing that extra mid-range that I liked so much from the MX Style Megabomb headpipe/4.1 muffler system. You will get slightly less pulling power on top end/length with the SX Style headpipe, but to me it was a minimal loss. Some less sensitive riders may not feel the loss of top end pull with the SX Style headpipe, but it’s something that should be noted. I prefer the SX Style headpipe on most motocross tracks simply because the KX450 pulls harder out of corners and I can shift to third gear sooner with the SX Style headpipe. 

Insert in…

You want to know a tip? Don’t throw out that insert that comes with your FMF 4.1 muffler system! Why? Because I actually liked the SX Style headpipe/4.1 muffler system better with the insert in. Why? Because it gave the muffler some added back pressure and gave me some added RPM response without sacrificing a lot of mid range pulling power. With the insert in the muffler, the KX450 now has increased (0-10% throttle opening) low RPM throttle response that I was missing through mid corner and had better corner exiting power. With the insert in you also will get more connection to the rear wheel and more traction when the track gets firmer. The sound of the 4.1 muffler with the insert in is also more pleasant and isn't as loud as the larger opening of the FMF 4.1. NOTE: Not all bikes respond to inserts/back pressure the same so just know that each bike is different. If you feel like you may need a little more low end throttle response from your FMF 4.1 muffler system, try the insert.  

 It’s tough to get more horsepower, added connectivity, as well as an overall better engine character than what a stock exhaust can give, but FMF did a good job with the 2020 Kawasaki KX450 SX Style headpipe/4.1 RCT muffler. It retained the stock system’s low end RPM response, while getting some added bottom end pulling power, as well as mid range meat coming out of corners. In order to get the SX Style headpipe when you order, you must order the SX Style headpipe separate and use the 4.1 RCT slip on. If you order the full factory 4.1 RCT system you will be getting the MX Style headpipe. The SX Style headpipe costs $349.99 and the 4.1 RCT slip on will run you $549.99. The FMF 4.1 RCT muffler also comes with a mounting bracket for the subframe tab to ensure that the tab will not break or crack. Overall, I think this is a good upgrade to your 2019-2020 K450. 

If you have any questions about this test please feel free to contact me at kris@keeferinctesting.com. I can guide you through any questions you may have. 

FMF Factory 4.1 Slip-On (2019 Yamaha YZ450FX)

Story By: Michael Allen

The simple fact that more manufacturers are offering off-road closed course competition bike’s brings a smile to my face since at heart I’m an off-road lover. That being said I feel like most manufacturers should know that 99% of all off-road racing organizations require race bikes to be equipped with a spark arrestor. Although the bikes are really good in stock trim, this issue has opened up a nice market for aftermarket exhaust manufacturers to be able to come in and save the day while making bikes race legal. I recently ran into this issue when I decided to race our 2019 Yamaha YZ 450FX at a local District 37 Sprint Enduro and realized last minute that I needed a legal muffler. I made a couple calls, but before I knew it FMF saved the day and I had a slip on Factory 4.1 on its way (two days before heading to the race). 

When I got the new 4.1 slip on muffler I immediately installed it, which was very self-explanatory and the fit and finish of the stainless can mated to the carbon endcap was top notch. Now here is the part of the story where Kris gave me crap about the spark arrestor… Admittedly I was putting on the muffler last minute and rushing to get all of my stuff ready to race the next day and I did what everyone says not to do; I assumed…. I assumed that the muffler came from FMF with the spark arrestor screen already installed, so I didn’t even think twice before loading up my bike and heading to the race. Well… I soon found out (thanks to my friend Brendon) that I didn’t have a spark arrestor because as Kris warned me about (and I forgot) FMF puts the insert in the bottom of the muffler box, where it stayed in my recycle bin until I got home that night. Luckily I was able to squeak through sound and spark arrestor testing and go to the start line. 

Initially what I noticed when I fired the 450FX up was that the new muffler was slightly louder (without the screen insert) than the stock muffler. This slightly louder sound was deeper than the somewhat raspy sounding stock muffler. The performance of the stock muffler was by no means hampering the 450FX power character, in fact it was quite good, but like I said, I needed a spark arrestor. The new 4.1 has a larger opening than the stock muffler, which in turn gives the 450FX slightly less back pressure. With a little less back pressure the FX lost a touch of smoothness in the very bottom end, giving the bike a more on/off feel. The tradeoff for the on/off feeling on the other hand was that the bike gained some over-rev and seemed to pull slightly longer into the RPM range. During the race I changed maps to try and smooth out the bottom end which helped, but didn’t completely remedy the bottom end touchiness. After getting home, going into my recycle bin (thankful the trash man didn’t come) and installing the spark arrestor insert, the bottom end delivery smoothed back out. With the insert comes a quieter sound, which was welcomed as well as some added back pressure. The back pressure gives this bike a little more lugability without wanting to flame out, so I didn’t have to worry as much about covering the clutch in tighter sections of the trail. 

The bottom line is that all bikes marketed to off-road racers should come with spark arrestor inserts, they don’t. That being said, FMF has done a great job at providing the off-road community a multitude of choices for whatever their specific type of riding entails. From full titanium systems, to more affordable aluminum slip on mufflers, FMF seems to have all the bases covered. At $449.99 for the stainless/carbon slip on that I installed, I think it’s a good combination of not breaking the bank while still looking slick at the track (not to mention that it takes almost two full pounds off your bike). If you have any  questions, or just want to tell me I’m a dumbass for not seeing the spark arrestor in the box, feel free to reach out to me at Michael@keeferinctesting.com . 

FMF 4.1 RCT Titanium Muffler System (2019 Kawasaki KX450)

The 2019 Kawasaki KX450 is the most improved machine of the new year, hands down! It has a very responsive engine character, comfortable suspension, a lightweight feel and cornering that is very neutral. I will be the first one to admit that I get nervous about sticking on any type of aftermarket muffler system when I really like the stock power curve of any machine. Sometimes aftermarket mufflers are just smoke and mirrors. They are lighter, titanium, look cool, but in the end they are no better than your heavy, ugly, big stock muffler. While I was testing the 2019 KX 450 earlier this year I could hear this little voice inside my head say “it’s going to be tough to make a muffler that is better than this stock one”. Fast forward to a few weeks ago and a shiny new FMF 4.1 RCT titanium exhaust shows up at my door, to be evaluated on the green machine. I sat on it for a week knowing that this new, shiny, lightweight piece of FMF artwork might not be better than the current monstrosity that is on the 2019 KX450. Nonetheless I installed the FMF system (which was easy I may add) and headed to the track to give it a go. 

The stock power curve of the 2019 KX450 engine has a snappy throttle response (with a free feel to it) and at times can almost be too much through corners with the standard green coupler installed. Once rolling on the throttle and passed the corner, the power is not quite as strong as the Honda or Yamaha, but still creates a easy to ride power feel on the track. I didn't necessarily need more rpm response with the 2019 KX450, but I wouldn’t mind some more meat through the mid to top end range. Bolting on the KX450 FMF Factory 4.1 RCT system is by far the easiest system I have installed on any 2019 machine. Installation literally took me through two full songs on the “Classic Rock” station on Pandora. Not bad! The 2019 Kawasaki is a light bike stock, but FMF sent me the full titanium system, which dropped the Kawasaki’s weight by 2.9 pounds from the stock system! To me the titanium FMF 4.1 system is one of the most stunning aftermarket mufflers you can put on any bike. I love the blue anodized finish as it looks good on almost every make and model machine there is.

FMF builds great looking mufflers! 

On the track the FMF 4.1 makes a slightly smoother bottom end power delivery, but keeps that exciting RPM response. Where most of you will feel your hard earned money is in the mid range pulling power when exiting corners. The stock system feels empty in this area, but the FMF fills in the power through the mid-range. What I mean by “fill in the power” is that the FMF system actually feels like it is shooting forward, as soon as you shift into third gear, unlike the stock Kawasaki’s power where it lacks some “meat” through the mid-range. The FMF 4.1 increases that mid range area and gives the rider some more freedom to be lazier in third gear. That is great news for all you vet riders out there, trust me! Top end is also increased slightly and you get increased pulling power near the end of each straight with the FMF. Over-rev is slightly increased as well with the 4.1 (over the stock muffler) as I could leave the KX450 in second and third gear slightly longer. The one downside to me is that it is loud sounding (compared to the stock system). It has more of a deeper/throatier pitch to it, which makes it sound louder than the stocker. 

I tested couplers along with mapping with the Kawasaki R&D guys and came up with a couple options for you (see attached maps). The white coupler map is better for bottom-mid range power, but the black coupler map is slightly better from mid to top end (the black coupler map is what I am running now). The good news is, unlike last year, the 2019 KX450 FMF 4.1 system will not have that de-cel popping with either coupler (along with these installed maps), which is a huge plus when it comes to a clean ignition/fuel mapping power feel.

Black Coupler Fuel Map 

Black Coupler Ignition Map 

White Coupler Fuel Map 

White Coupler Ignition Map

At the end of the day the FMF 4.1 RCT full titanium muffler system delivers a smoother roll on bottom end delivery with a mid to top end puling powerl that is better than stock (along with improved mid-top end RPM response). I will say this again….Being able to achieve a power delivery that is better than what an OEM muffler system can give you is very hard to do. FMF has achieved this with their 4.1 system on the 2019 KX450. Not only does it make power, but it also takes off some weight and looks better than the stock bazooka. I wanted some added control down low and more mid range (on the 2019 KX450) so with this FMF system I got what I was looking for. I am not going to sit here and tell you guys that every FMF system, for every machine is better than stock, but with this one they knocked it out of the park. Don't be scared to try the maps that are attached above, because with today's four-stroke technology, getting the correct mapping for a certain muffler can really make a difference. 

Attention mechanically inclined riders!!!!! Please note that re-packing of the FMF muffler is important for the can’s lifespan. The muffler portion (or can) will start to leave hot spots/scarring when the packing starts to burn away from inside. Once you start seeing these “hot spot/scars/markings” on the muffler, remove and re-pack it ASAP. FMF offers re-packing kits and taking the can apart to re-pack is not that hard to do. I get around 12 hard engine hours before I see these markings and have to re-pack. If you run it past the recommended time, you run the chance of hurting performance and damaging the core (or perf) inside the muffler. Don’t be a dummy and waste your money, re-pack your muff! 

If you have any questions about this test please email me at kris@keeferinctesting.com

FMF 4.1 RCT Titanium Muffler With Mega Bomb Plus Headpipe

If you have kept up on my social media channels (@kkeefer120, @keeferinctesting) you will know that I have been riding the crap out of the 2018.5 Husqvarna FC450 Rockstar Edition and 2018.5 KTM 450 SX-F Factory Edition machines. I enjoy riding these two machines because they are easy to ride, well balanced and feel extremely lightweight when cornering. I do however wish they had some more RPM response and low-end excitement. Since the new Husqvarna RE’s and KTM FE’s are not coming with an aftermarket muffler this year I wanted to get my hands on FMF’s version as soon as possible to give you all some feedback, just in case you wanted to add some more bling and possible horsepower to your new machines.

The new FMF 4.1 RCT Full Titanium Muffler System that you see here will fit on either your 2018.5 KTM Factory Edition or your Husqvarna Rockstar Edition. The FMF 4.1 system went on easy on both bikes and took only a few minutes to install. Thank you to Husqvarna and KTM for making the new bike much easier to change a muffler. Gone are the days of dropping the shock and cursing in the garage just so you could get your new muffler system on. I tested the FMF 4.1 muffler system at several tracks on both bikes and had similar results at each track I tested at. In stock form the KTM Factory Edition has a little more throttle response and bottom end pull than the Husqvarna Rockstar Edition, but the RE pulls slightly longer up top. 

With the FMF system installed you will not be getting increased bottom end pull on either machine (compared to stock), but you will be getting a little more bottom and mid-range RPM response (or throttle crack for you not testing type readers). I noticed the added RPM response more on the Husqvarna, especially on low RPM, out of corners. The FMF system makes each machine’s engine character slightly more free-feeling and exciting. I also appreciate that I am not getting any added de-cel popping (or lean sensation) with the FMF system and both bikes ran just as clean with the FMF system on than it did with the stock muffler. Where you will notice the most improvement with the FMF system is through the mid-range. The mid-range “meat” you will get out of the FMF 4.1 system is downright impressive. Rolling the throttle on out of corners and accelerating you will notice an increased pulling power that wasn't there with the stock muffler on either machine. Whether you're coming out of a corner in second or third gear you will notice some extra horsepower getting to the next obstacle. With the added mid-range meat of the FMF system it really helped some of the gearing issues I had at tighter, less flowy tracks I tested at. Gaining some mid-range let me use third gear in some corners that was tough for me to decipher which gear was better. With the stock system I would roll into these corners in second gear and have the right amount of "pop" to get me out quick, but I had to shift early once exited, to keep the rear wheel from spinning. Third gear was too tall of a gear to get me out of the corner quick, but provided less wheel spin on the exit, so it was always a struggle for me to decide on which gear to use when being pressured from behind by another rider. With the FMF installed I could easily use third gear and have enough "pop" to get me out of the corner in a hurry, yet it kept the wheel spin to a minimum by being able to use a taller gear. So basically what I am saying is that FMF’s 4.1 system made me think less and twist the throttle harder, something I like doing. I didn't get any more top-end with the FMF installed, yet it didn't take any away from either machine. I did notice slightly less over-rev with the FMF system (from stock) when I got lazy and tried to wring each machine’s neck out in second and third gear. I don't mind not gaining anymore top- end and losing a touch of over-rev with these two models, because they are one of the most powerful engines in these ranges. I am not looking to own a top fuel dragster here. 

You have heard me say it time and time again that it's tough to beat a stock muffler system these days. You see more and more after market companies taking the time to release their new model systems because it’s not that simple to make a muffler system better than stock. FMF made their new 4.1 RCT titanium muffler with Mega Bomb Plus headpipe not only better through the mid-range, but a full pound lighter on the scales as well. If you just purchased your $10,000 plus Husqvarna RE or KTM FE and still have $1099.99 burning a hole in your pocket, I approve of this new system Lil D and the boys over at FMF developed. Head over to fmfracing.com or give them a call at (310) 631-4363 to see when this system will be available. 

FMF Factory 4.1 RCT Full Muffler System Product Review

It’s hard sometimes to get more power out of newer four-stroke models nowadays with aftermarket mufflers systems. To be honest with you most stock systems are pretty damn good and aftermarket muffler companies like FMF work really hard to try and give you that little extra bit out of a system. I can sit here and tell you that FMF is one company (of only a couple in existence) that will take the time to listen to the proper feedback (either from me or other media testing outlets) and make the necessary changes to alter a new four-stroke machines power in the right direction. The key word here is “alter” and maybe not “gain”. Yes, in this article you will hear me talk about “gaining” a little pulling power, but to me the configuration of the 2018 Kawasaki KX450F FMF 4.1 RCT Muffler System power delivery is more “altered” from stock than anything. 

The stock power of the Kawasaki is unchanged for 2018, but that doesn't mean it’s not a great bike. The engine has a snappy throttle response with a free feeling, on de-cel, without much engine braking. Once rolling on the throttle, the power is not as strong as the Honda or Yamaha, but still creates a lightweight feeling on the track. I didn't necessarily need more rpm response with the KX450F, but would like more meat through the mid to top end range. Bolting on the KX450F FMF Factory 4.1 system is bar far the easiest system I have bolted on for 2018. It took me literally two full songs on the Metallica Pandora station to change the muffler. The Kawasaki is a light bike stock, but I chose to go with the full titanium system that let me drop 1.8 pounds from the stock system! Visually the titanium FMF system is one of the most stunning aftermarket mufflers you can put on a bike. I love the blue anodized finish as it looks good on almost every make and model machine. 

On the track the FMF 4.1 on the KX450F makes as much bottom end power delivery as stock and keeps that peppy/exciting RPM response. Where the FMF 4.1 system really impressed me was mid range pulling power when exiting corners. The stock system feels empty in this area, but the FMF fills the power-feeling in through the mid-range. What I mean by “fill the power in” is that the FMF system actually feels like it pulls as soon as you shift into third gear unlike the Kawasaki’s power where it feels like it lacks some pull through the mid-range. There is a dip in the Kawasaki’s mid to top end power and the FMF brings back some meat through that area, which in this case “fills in” that area. Top end is also increased slightly and you get increased pulling power near the end of each straight with the FMF. 

I did go back and forth with the couplers on the KX450F and came to the conclusion that although the lean coupler is better for bottom-mid range power, the standard coupler is slightly better from mid to top end. I will have to say when you do go to the lean coupler that the KX450F will pop more on de-cel with the FMF system than the stock muffler. With the standard coupler de-cel pop is minimal and not as noticeable with either system. 

At the end of the day the FMF 4.1 RCT full muffler system is better than stock and that is not easy to do these days. It takes off some weight and looks better than the stock monstrosity. To me there is no negative with the FMF system and that is rare in an aftermarket muffler. I have tried other FMF mufflers, on some other models with some negatives, but the KX450F muffler is a good buy. Please note that re-packing of the FMF muffler is important for the can’s lifespan. The muffler portion (or can) will start to leave hot spots/scarring when the packing starts to burn out inside. Once you start seeing these “hot spot scars or markings” on the muffler, remove and re-pack is recommended. FMF sells re-packing kits and taking the can apart to re-pack is not that hard to do. I get around 10 hard engine hours (these are pro type hours) before I see these markings and have to re-pack. If you run it past the recommended time, you run the chance of hurting performance and damaging the core (or perf) inside the muffler. Kudos to FMF for building a good KX450F system and moving the power around slightly and gaining a little as well. If you have any questions about this test please email me at kris@keeferinctesting.com 

Bonus: If you listen to my Keefer Tested podcast you know that I rate some parts and motorcycles by a numeral system. I wanted to break down the FMF system to the stock system for you all below. If you don’t know what these numbers mean, please go listen to show #3 “How To Test” and you will understand better what these numbers mean. 

Stock/FMF:

Bottom End: 3/3

Mid-Range:  3/3.5

Top End:      3/3+

Over-Rev:    3/3+

Bottom End RPM Response:  3/3

Mid RPM Response:               3/3.5

Top End RPM Response:       3/3+