How about a 2 stroke pipe on your 4 stroke? Wave of the future?

[onformula1]

How about a 2 stroke pipe on your 4 stroke? Wave of the future?

It's pretty close (A little smaller) Who's going to build the first one for a 200X or 350X?208715208716

[El Camexican]

I believe the FMF power bombs still run the header pipe through the expansion chamber and just vent it. Was thinking of trying it on my YTM just for grins.

[Ghostv2]

I think there was a thread here a while back of actual tests of a manufactured 4-stroke pipe with a expansion chamber and it didn't turn out so well. I'll have to try to dig to find it. I don't know if it was lower horsepower or what in the end.

[90guy]

Yup fmf power bomb and a fmf mega bomb. I've got a power bomb on my bike. I've heard the mega bomb is just to much and people are saying they are getting loses. Not to sure though. Either way the power bomb isn't to bad. Did notice by the feel of the seat gain.

[RIDE-RED 250r]

I can't for the life of me see how an expansion chamber on a 4-stroke header can be anything but snake oil. Unless I don't fully understand it, the exhaust system on a 4-stroke is just a means to expel exhaust gasses, unlike on a 2-stroke that utilizes reverberating sonic wave to force part of the intake charge that goes into the header back into the combustion chamber. 4-strokes do not work in this way at all in my understanding...

Wonder why the full length headers on my SBC don't have expansion chambers.... ;) And I haven't seen anything other than pretty much straight pipes on any sort of race car either.... Just free flowing...

Correct me if I'm wrong on this guys... I just don't see it

[Dirtweed]

My 1990 Suzuki LT250s Quad came from the factory with a little expansion chamber (power bomb). Not sure how much use it was.

[nstyle73]

Car exhausts are tuned as well. Those SBC headers have to have the same length tubes for each cylinder and if you want to run them open, the length of the extension beyond the collector will affect torque, so 4 strokes do respond to exhaust pressure which may be where the "power bomb" is comes in. I am not saying that it works or doesn't, but an expansion creates a pressure drop, and pressure differential causes flow rate. A tapered section acts as a nozzle and by changing the taper, you can tune where your sonic waves occur. That is my limited understanding of the theory based on my Gas Dynamics courses. Practical application is probably spoken to by someone else.

[redsox]

i don't buy it either. What are they claiming it does? is it somehow relieving restriction? i'm no 2-stroke guy, but i know a little about 4 strokes. i just can't see an advantage. Are you sure its a performance mod? not some type of environmental BS or noise reducer? less vibration to disturb the piping plovers?

[Dave8338]

Car exhausts are tuned as well. Those SBC headers have to have the same length tubes for each cylinder and if you want to run them open, the length of the extension beyond the collector will affect torque, so 4 strokes do respond to exhaust pressure which may be where the "power bomb" is comes in. I am not saying that it works or doesn't, but an expansion creates a pressure drop, and pressure differential causes flow rate. A tapered section acts as a nozzle and by changing the taper, you can tune where your sonic waves occur. That is my limited understanding of the theory based on my Gas Dynamics courses. Practical application is probably spoken to by someone else.

Hmmmm.... and I suppose that by a change in the exhaust port, by creating a "taper" shape in the head, just after the exhaust valve, one could achieve the same results. :naughty:

[RIDE-RED 250r]

Car exhausts are tuned as well. Those SBC headers have to have the same length tubes for each cylinder and if you want to run them open, the length of the extension beyond the collector will affect torque, so 4 strokes do respond to exhaust pressure which may be where the "power bomb" is comes in. I am not saying that it works or doesn't, but an expansion creates a pressure drop, and pressure differential causes flow rate. A tapered section acts as a nozzle and by changing the taper, you can tune where your sonic waves occur. That is my limited understanding of the theory based on my Gas Dynamics courses. Practical application is probably spoken to by someone else.

I completely get what you are saying, and thanks for the explanation. It does make sense.... But with this little setup, despite creating a sort of exhaust pressure reduction in that little chamber, it is still going to be counteracted by the end of the "stinger" (if you will)?? I understand that the amount of back pressure in a 4-stroke exhaust does have an effect on the power and torque curve and there is a certain amount of tunability there..

But the expansion chamber design on a 2-stroke pipe has nothing to do with back pressure, it is made to utilize sonic waves of pressure bouncing off the far end of the expansion chamber and feeding back into the cylinder before the piston closes off the exhaust port... And then you can play with back pressure tuning based on stinger size and length. Your back pressure is going to be directly effected by and tied to the smallest component in the system, isn't it???. Again, I am not seeing the benefit of this expansion chamber on the 4-stroke engine.. I just don't get how a sonic wave bouncing back to the exhaust port benefits when your exhaust valve is likely to be closed when it gets there?? Where is that sonic wave supposed to go? And what is it supposed to be carrying there once it gets there?? If jetted right, there won't be any significant amount of unburned fuel getting stuffed back in there... and if there was, would it really be helpful??

I hope you don't think I am trying to pick a fight or be smart with you. I am trying to understand this and it is in fact a beneficial addition to a 4-stroke exhaust. Bear with me, sometimes I'm a slow learner. :beer

You know what... I just had a thought... I wonder if it is more to dissipate heat more efficiently??? If so, you may be able to lean the jetting slightly which would give a slight boost in the seat of the pants... Thoughts?????

[Dave8338]

If I had to guess, and it is only a guess, they are tuning for an exhaust tone, lower in this case, more so than any exhaust benefit from reverberations. As mentioned, on a 2-stroke, it is done to keep the fuel charge in the cylinder. Valves on a four stroke, already do that.

[RIDE-RED 250r]

If I had to guess, and it is only a guess, they are tuning for an exhaust tone, lower in this case, more so than any exhaust benefit from reverberations. As mentioned, on a 2-stroke, it is done to keep the fuel charge in the cylinder. Valves on a four stroke, already do that.

Thats possible... But it's touted as a performance enhancing part isn't it??

But now I'm re-hashing what nstyle73 posted... Maybe it does give the effect of more free flowing exhaust without the extra noise of a more free flowing exhaust of conventional design... But I'm still hung up on if it really works that way.. In my mind it still seems as though it will only flow as much as the smallest part of the system. So what is gained by blowing out the header for 3" then choking it back down???

[yaegerb]

From FMF:
"The redesigned PowerBomb is a four-stroke header that incorporates FMF’s patented PowerBomb module at a precise location in the initial stage of the header. By positioning this “Bomb” at a key point in the system, increased performance and flow is achieved through the expansion and contraction of exhaust sonics through the system. Result is a flow increase of nearly 10% The outer chamber in the Powerbomb allows the air to expand, cool and ramp back up at a higher velocity. Additionally, the PowerBomb is a “pre-muffler” of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases). On some models, you can choose between a moto or supercross version. The supercross version is designed for more low to mid-range power where the moto version is focused in the mid to upper RPM range."

[redsox]

"ramp back up"?? meaning towards the muffler at a higher velocity? so it's claiming to increase flow. not claiming to "ramp back up" towards the chamber??? increase flow by bouncing gases back to the chamber? Che? Am i reading that right? I've never heard of speeding something up by putting it in reverse. As far as cooling, it would stand to reason that an area allowing a larger volume of air and a greater surface area would be cooler, but i can't see how it would create enough of a temperature difference to increase performance. i'm calling shenanigans. IMO its a cherry-bomb that makes the bike sound bad-arse and therefore it "seems" faster. Right? I'm ok with that, but it just is what it is. And Nstyle, very well put, and i agree. but all that tuning, if i understand it correctly, is managing the flow of gases AWAY, and in relation to each other. Correct? would the same apply in this case?

[fabiodriven]

I'd like to see a cutaway. If there's a pipe protruding inside that chamber coming from the exhaust side, there's your low pressure zone. I could see that having an effect in that case. I've seen the effects of low pressure zones on wood stoves enough to know the theory is no only sound, but proven. Seeing it in action on a stove would be like watching what this pipe does in slow motion.

[90guy]

Fabio here is a cutaway. It's a pipe with holes with a bigger pipe on the outside.

[fabiodriven]

Belay my last. That does nothing.

[RIDE-RED 250r]

Belay my last. That does nothing.


I agree Fabs... nothing more than a silencer.. Snake oil.

[nstyle73]

Definitely looks like a silencer. Again, I am not an expert, but I do find this stuff interesting. It is a larger volume which decreases pressure. The sonics are much different than a two stroke as stated above by others. I believe in a two stroke you are looking for sonic shock waves which occur when a gas is traveling at the correct speed with respect to the nozzle diameter to create a shock wave. Wave placement get much more complicated with sonic velocities. I do not know what the exhaust speeds for an atv range to, nor do I even have a guess, but I am guessing that on a four stroke they are not looking for that type of wave as, was stated above, the exhaust valve controls the combustion chamber. However, the mass flow rate of a compressible gas is temperature dependent and an expansion creates a temperature drop. To maintain flow rate of a cooler gas, the velocity must increase. To increase the velocity, without increasing the temperature, the "nozzle", or diameter must again be reduced. Again, those that apply this practically would be better suited to elaborate as I am simply going from scratch. My experience is that the people that design things start with a better understanding because those that came before them in their field already did the ground work and established baselines. But yes, looks like a silencer, walks like a silencer......

[NeverLift]

On Suzuki and Yamaha inline 4 sport bikes they have a valve in the exhaust that opens and closes with rpm range. This sends the sonic waves back at the correct moment to hold the fresh mixture in the cylinder during overlap (when both the intake and exhaust valves are open at the same time). There is significantly more overlap on a motor that makes high rpm power than a little torque motor that all trikes have. Being that they are putting these on DOHC hi reving new 4strokes I can see why it works. The expansion chamber is basically the same idea.

[onformula1]

Info for the bike from the original post.

This is from- KTM via MXA.

It may look like a two-stroke expansion chamber, but it actually a stylized resonance chamber that fits over the existing head pipe. KTM calls it FDH which sounds like a florist shop. The 250SXF Factory Edition has the old school tube-style resonance chamber.

New Flow Design Header (FDH) with an integrated sound resonator that is also designed to increase power along with a new lightweight silencer that is 40mm shorter than the previous design for quick throttle response.

This is from- KTM via Dirt Rider.


The exhaust is new on both bikes, but different. Both machines have a different head pipe and their muffler is now 40mm shorter. The new exhaust moves the muffler a total of 60mm closer to the center of mass (forward). With internal muffler changes, the new muffler is also said to be quieter. [A quick editorial note: KTM is great about making sound-responsible bikes. This goes a long way toward improving the sport for everyone. Thank you, KTM, for your approach to bike sound.]

50 – the bulged 450 head pipe is called a Flow Design Header (FDH), and it looks wild. It basically looks like a small two-stroke expansion chamber, and is designed to improve power and throttle response while helping reduce sound.

[El Camexican]

Not to get too technical, but there MUST be something to this. I believe the diagram below clearly proves that enhanced expulsion of gases by varying the diameter of the pipe throughout the length of the system is a very real thing!
208789

[aramid]

.
I'm definitely not an exhaust scientist but here's some general info.

The bulge in the pipe on the bike is a simple “resonator” as was mentioned . . Some cars came with resonators from the factory . . the 65 thru 68 dual exhaust mustangs had them.


“In a Helmholtz resonator design, a cavity is attached to the exhaust pipe. At a specific frequency, the cavity will resonate and the waves in the exhaust pipe are reflected back towards the source. However, there are also pass band frequencies where the resonator has no effect and so resonator muffler design is targeted to specific frequencies where the majority of attenuation is required. In some designs, the muffler has several resonators of different sizes to target a range of frequencies.”


This article below discusses sound waves to some degree and the chamber attached to the pipe in the photo which is referred to as a “helmholz” design or resonator .

http://www.paraglidingteam.nl/PPGTechnics/sound%20and%20noise/Mufflers/1155795969.pdf


“The theory of Helmholtz resonators is used in motorcycle and car exhausts to alter the sound of the exhaust note and for differences in power delivery by adding chambers to the exhaust. Exhaust resonators are also used to reduce potentially loud and obnoxious engine noise where the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.

In some two-stroke engines, a Helmholtz resonator is used to remove the need for a reed valve. A similar effect is also used in the exhaust system of most two-stroke engines, using a reflected pressure pulse to supercharge the cylinder (see Kadenacy effect.)”

http://en.wikipedia.org/wiki/Helmholtz_resonance


”The outer chamber in the Powerbomb allows the air to expand, cool and ramp back up at a higher velocity.”

I’m not saying their design serves no purpose but this portion of their explanation is not exactly correct . . cool air is more dense than hot air and will move more slowly thru an exhaust.

The purpose of the exhaust is to exit with the highest or the most optimum velocity possible combined with enough flow so it does not cause reversion . . if the exhaust exits with sufficient velocity, it will help pull the air/fuel mixture into the combustion chamber thereby creating a cleaner and fuller charge . . these things occur because the intake valve opens before tdc while the exhaust valve is still open which closes after tdc. . these two timing events are what is called “overlap”.

If you remove the exhaust from a 4 stroke [and 2 stroke but their system is obviously different] if will loose maybe 60 -70% of its power and it will only rev to less than 1/2 of what it would if it had a properly tuned exhaust . . I’ve done it on more than one occasion, lol.

If you put a 1/2” diameter pipe on an engine that needs a 1” one, it will impede the exhaust flow which will thereby reduce the intake flow plus more exhaust will remain in the cylinder contaminating the intake mixture reducing its effectiveness.

Once an optimum size and length pipe is determined for a particular set up, both reducing or increasing the size will change the power characteristics.

It’s partially a case where bigger is not better . . I have seen a lot of people change their exhaust only to lose overall power.

When one talks about “backpressure” it is the same as talking about exhaust velocity and volume . . if you reduce the exit size of a properly tuned exhaust pipe by around 50%, it will significantly reduce overall power and peak rpm as well as a few other "unbeneficial" things.

High end multi cylinder headers also use merge collectors . . in some racing apps, headers that have one or two larger tubes attached to the tube exiting the head are used . . these are referred to as “stepped” headers.


Dyno tests on different header sizes . . the biggest headers reduced overall power.

https://www.youtube.com/watch?v=O1bXPNy1Yn4


dyno tests on different collector lengths

https://www.youtube.com/watch?v=1ywUEz5XtdE

[fabiodriven]

.The bulge in the pipe on the bike is a simple “resonator” as was mentioned . . Some cars came with resonators from the factory . . the 65 thru 68 dual exhaust mustangs had them.

Excellent post and the most helpful thus far for me personally. Thank you.

Not just old Mustangs came with resonators from the factory. They may have been amongst few that came from the factory with ONLY resonators (glass packs), but the truth is most cars come with resonators these days right from the factory but they are incorporated with the entire exhaust including the cat(s) and muffler(s) in order to control "resonance". If you're not familiar with that word, it's that really powerful drone that is at that "just right" frequency when you're cruising in your vehicle under a mid to light load. It's a low frequency but it's loud. A lot of times it will be especially pronounced with an altered exhaust system in any car or truck. I worked for many years at a custom exhaust shop that really pushed Flowmaster, and we had a fair amount of people come back complaining about that "drone". Sometimes we'd try and swap the muffler out from a 2 chamber to a 3 chamber, or a 3 chamber to a big-block Flowmaster, but many times we'd end up installing resonators in addition to the mufflers.

As a kid I was always fascinated by V8's with glass packs. The trend has been somewhat passe for many years now, yet I never stopped using them. I've always used glass packs (resonators) on my V8 gas engines and I always get tons of praise, yet not many other people do it. The rasp they give, I've never been able to explain but the above post has helped me understand it. A healthy V8 at WOT with glass packs is just such a piercing sound, it forces you to hear it. You look to see what that noise is whether you love it or hate it, but you can't not look.

I have learned over recent years the huge effect exhaust has on both engines and wood stoves, to reference that again. The fact is that exhaust has a lot to do with the combustion process, which obviously happens before the exhaust comes into play, might seem odd at first. It is still fact however. I think knowing now more about what that rasp is that glass packs produce I might find it a little more likely that these little resonators are doing something. KTM is a pretty stand up company as we all know, it ain't Kimco or whatever the fork. I'm guessing they know a thing or two more than us on this particular front, although obviously we're still smarter, but I'm willing to bet this wasn't done without plenty of research and money spent. I bet the gain isn't huge, but there could be a gain. Not to mention, if a gain were found with something like this, even a small gain, it could be the infancy of an idea that might lead to a 30% horsepower gain as this technology evolves. Stranger things have happened.

[redsox]

good thread. i've learned a bunch. i'm sticking with science on this one though. floating valves or not, a four stroke is not a two stroke. this pipe is not supercharging the chamber of a valved engine at any rpm. exhaust flow is important. vacuum pressure, air speed, restriction, flow, etc, etc, etc, are all factors that must be managed. i would never argue against that. that being said, i cannot understand how the design in this bike increases performance. it makes the bike quieter. if KTM's argument is that this bike has a 3-5% increase in tourque over an equally quiet comparable bike because of this "megabomb" then i'd agree. but that is semantics. the "equally quiet" is the qualifier. it is just double-speak for "we can make your fast bike quiet". That is my position. One thing to consider, in KTM's favor, are federal noise emission restrictions that apply to manufacturers across the board. If any stock bike produced had to be within federal noise guidelines, and this particular bike would allow for more power while still maintaining the noise guidelines, then, I suppose, this is a performance enhancement. But, if you replaced the "megabomb" with a conventional pipe the only change would be sound, IMO.

[RIDE-RED 250r]

Good post Aramid!

But like Redsox, that point where they talk about it's noise reduction catches my attention. So now that it's being called a resonator, and resonators seem to be more about sound than anything, I think you guys are right. It's starting to look like it is a way for them to make a higher performing exhaust while still keeping it within noise limits. Also noted how they talked about that design allowing them to change the silencer position for better weight distribution..

Interesting topic for sure.

[aramid]

.
thanks ride red and Fabio and thanks redsox for the info . . I think redsox is correct and it is the same thing I was going to post last nite in reply to fabios post but I hit the wrong button on the computer and it quit working so I am on another computer and need to find some 12 year old to fix the other one, lol.



just another bit of fun info you guys may already know but here it is for some others . . neither air nor water like to bend . . it will flow thru a straight pipe faster than it will thru a bent pipe . . putting a bend in a pipe to go over the rear axle on a vehicle will slow it down slightly . . this is the same for 2 stroke pipes also, plus sound waves are round by nature . . when you change their shape it alters their nature such as sound and sped etc and since sound waves are merely pressure waves, they affect exhaust flow also . . there was one test done on a 2 stroke pipe where a pipe was made that exited straight out of the cylinder and had no bends and a second pipe was made of the exact same proportions with bends in to fit the bike and the one with bends did not work as well overall.



this goes for intake and exhaust ports also . . if you look at ultra high perf auto cyl heads where room is not a concern, the ports are made as straight as possible . . also, velocity stacks are often used partially to eliminate the bends in the conventional intake manifold . . in addition to the comment made by a few regarding sound waves affecting flow/perf, tpi which as some know means tuned port intake or tuned port injection means that every runner is the same length and is also tuned to the engine buy having a specific length.



without going into much detail, there are pressure/sound waves in an intake that travel at ultra high speeds back and forth from the intake valve and they want these waves to be going into the intake valve just when it opens to help bring the fuel mix into the cylinder . . the problem is that these waves are apparently maybe 14 feet long so since it would be a bit impractical to make a 14 foot long intake, they divided the length of the wave by even quarters until the number was short enough that they could use it for an intake runner length . . this process is similar to cb radio antennas and i'm guessing other antennas as well, but this science is a bit beyond my pea brain ability to really understand no matter how hard I try.



as far as it applies to exhaust . . it is apparently similar which is why a certain collector length works best on exhaust as I think nstyle mentioned ut it is complicated in a different way where the sound/pressure wave exiting the pipe affects the exhaust so not only does changing the length of the pip affect performance, on a 4stroke at least, the shape of the exhaust exit also affects performance and this gets into megaphones as another here mentioned . . in short, the taper of a megaphone affects power . . it basically takes x amount of power and spreads it over a slightly wider range, therefore, they do not really make additional . . one poor way to explain it would be to imagine you have a spoonful of butter [the butter will represent the total amount of horsepower] and you place it in the center of a piece of toast, and you eat the toast, when you get to the butter you get a whole bunch of it all at once . . if you spread the butter evenly over the entire piece of toast, you still have the same amount of butter but you get an even butter favor with every bite but you never get a bunch of flavor all at once . . another example might be a tecate vs a Honda . . both are excellent bikes. and both are fast, but anyone that has ridden them both in box stock form knows the Honda has a nice smooth predictable power delivery and the tecate...well not so much, lol, but I like them that way.



if one is drag racing or dong the dirt track mile etc, their engines are operating over a narrow rpm range and at the top of the rpm range, so to take some of this power and spread it over a wider rpm range than the vehicle operates at is pointless and will make the vehicle slower for the purpose it is intended for . . conversely, taking an engine with a narrow power band and trying to use it in a motorcross bike simply won't work very well.


http://www.museumofamericanspeed.com/RS/SR/Alternate/32/2903~2_R_15e1535f.jpg