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?

[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.

[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.

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.