Skip the muffler all together

[cpr]

Where on earth did you get that muffler? I want one for my 380A! What does it sound like?

It's a header for a tuned pipe on the kart engine.

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[logging22]

Love that sound!

 

[LegDeLimber]

Someone had a link to a company's pdf brochure.
Inside of that, was a cutaway of their muffler.
it had an inner chamber that was claimed to use the resonance
to return a pulse and reduce the out flow of the fresh charge.
Sorta like an expansion chamber
but with out the intended extraction affect.
The inner chamber looked like a cross between a crack pipe
and one of those dunky drinking bird toys.

Aha, found it.
My apology to the poster, for not remembering who it was.

scroll down to the "SLR" part.
http://www.dolmarpowerproducts.com/downloads/1688/2012Catalog.pdf

Actually had been wondering about this type idea for awhile, myself.
but for the idea/purpose of a mini extractor though.

 

[edisto]

Someone had a link to a company's pdf brochure.
Inside of that, was a cutaway of their muffler.
it had an inner chamber that was claimed to use the resonance
to return a pulse and reduce the out flow of the fresh charge.
Sorta like an expansion chamber
but with out the intended extraction affect.
The inner chamber looked like a cross between a crack pipe
and one of those dunky drinking bird toys.

From what I can see it is to improve emissions only. No other good reason to "stop" scavenging unless you have an effective way to generate negative pressure in the exhaust.

It looks to me like it operates on pressure, not resonance.

 

[LegDeLimber]

Yeah, I may be mangling semantics onsay they use a resonance
but it still going to be a rebounding pressure pulse that needs to be timed
with the engine speed.

Bottom line (for my thoughts at least) would be to try tuning to exploit
any available res for mimicking an expansion chamber.
I could be way of base in thinking that you could hit a useful frequency
and gas/charge volume in that size package.

looked at some pipe organ lengths to see what length tube would hit
oh say, 9000 rpm's and the pipe would have been longer than an expansion chamber
plus probably have a really uselessly narrow power spike/peak.

fun to ponder it though, as I've got much more "money" in my mental R&D
than in the real world.

 

[Chris-PA]

It looks to me like it operates on pressure, not resonance.

I've been wondering about that and I kinda think there must be a resonance component to it too. Otherwise it would be a volume of dead/stagnant gasses on an unused branch off the main exhaust path - it would effectively not be there, and the thing would just be a muffler with a tiny outlet.

 

[bootboy]

My understanding of it is that you need both pressure and resonance. A muffler has to achieve three main things these days: sound dampening, emission reduction, and back pressure. Improve one and the others suffer, it's a balance. If we throw out the emissions part of the equation It's possible to actually create a muffler that does the other 2 objectives better. It's possible to have a muffler that maintains adequate pressure but increased flow. How? Resonance my friends. A well designed muffler basically focuses and concentrates pressure only where it's needed, when its needed, over the exhaust port, ideally at the optimum working rpms of the engine. By doing so, you've allowed yourself to open up any part of the muffler that doesn't help create this effect. Thus allowing exhaust to exit the muffler much more quickly. Like I said though, noise reduction and emissions suffer.

 

[edisto]

I've been wondering about that and I kinda think there must be a resonance component to it too. Otherwise it would be a volume of dead/stagnant gasses on an unused branch off the main exhaust path - it would effectively not be there, and the thing would just be a muffler with a tiny outlet.

It's possible to have a muffler that maintains adequate pressure but increased flow. How? Resonance my friends.

Do a search for "tuned pipe" and find a picture of one. The reason people don't have them on their work saws is because of the size. The reason they have to be that size is for the pulses to be timed properly.

There is an inlet pipe, an expanding cone, a reducing cone, and an outlet.

The opening of the exhaust port creates a positive pulse. When it hits the end of a pipe, it reflects a negative pule that travels back to the exhaust port. The duration of the pulse can be increased by having a cone instead of an abrupt ending, which also weakens the pulse. This negative pressure helps to scavenge the cylinder. It works so well that charge is "pulled" into the system.

At the same time, the positive pulse continues towards the outlet. If the pipe is sealed, the positive wave is reflected back. Again, a cone will lengthen the duration of this positive pulse at the expense of the strength of the pulse. This positive pulse forces the charge back into the cylinder, basically acting like a supercharger.

The narrow outlet (or "stinger") is a restriction that is designed to produce some backpressure to help with the effect of the positive wave.

The only way to time the negative scavenging wave and the positive supercharging wave is to place the cones at the right distances in the exhaust path. Those distances are too far down the path to be practical for a chainsaw.

 

[sachsmo]

Yup,

just that easy.

ma mopar did lots of study and engineering on intakes back in the day using the same basic principle.

Remember the sonoramic long rams? Awesome torque for them big boats.

They shortened them but using the same principles they had the "short rams" for the SS cars.

They still dominate in the NHRA SS classes.

 

[Chris-PA]

Do a search for "tuned pipe" and find a picture of one. The reason people don't have them on their work saws is because of the size. The reason they have to be that size is for the pulses to be timed properly.

There is an inlet pipe, an expanding cone, a reducing cone, and an outlet.

The opening of the exhaust port creates a positive pulse. When it hits the end of a pipe, it reflects a negative pule that travels back to the exhaust port. The duration of the pulse can be increased by having a cone instead of an abrupt ending, which also weakens the pulse. This negative pressure helps to scavenge the cylinder. It works so well that charge is "pulled" into the system.

At the same time, the positive pulse continues towards the outlet. If the pipe is sealed, the positive wave is reflected back. Again, a cone will lengthen the duration of this positive pulse at the expense of the strength of the pulse. This positive pulse forces the charge back into the cylinder, basically acting like a supercharger.

The narrow outlet (or "stinger") is a restriction that is designed to produce some backpressure to help with the effect of the positive wave.

The only way to time the negative scavenging wave and the positive supercharging wave is to place the cones at the right distances in the exhaust path. Those distances are too far down the path to be practical for a chainsaw.

Yes, I understand pulse reflection - it actually is very similar to pulse reflection on electrical transmission lines and controlled impedance cables.

The exhaust pulse will reflect off of any change in area, either positive or negative depending on whether the pipe is open or closed as you wrote. The propagation speed of the pulse can be reduced by increasing the diameter of the pipe, but you cannot do this abruptly or you'll get a reflection - hence the cones to make a gradual transition. This is merely a way to make a pipe that is effectively longer. You can get the pulses to reflect multiple times, losing a bit of amplitude and getting a bit smeared out each time.

I'm still not sure how they would keep the gasses in this SLR chamber from stagnating without some kind of pulse/resonance tuning effect going on.

 

[sachsmo]

Yes, I understand pulse reflection - it actually is very similar to pulse reflection on electrical transmission lines and controlled impedance cables.

The exhaust pulse will reflect off of any change in area, either positive or negative depending on whether the pipe is open or closed as you wrote. The propagation speed of the pulse can be reduced by increasing the diameter of the pipe, but you cannot do this abruptly or you'll get a reflection - hence the cones to make a gradual transition. This is merely a way to make a pipe that is effectively longer. You can get the pulses to reflect multiple times, losing a bit of amplitude and getting a bit smeared out each time.

I'm still not sure how they would keep the gasses in this SLR chamber from stagnating without some kind of pulse/resonance tuning effect going on.

Most chainsaw pipes are multiple cones welded together to approximate the proper chamber.

if you had it all worked out a stamping, or better yet a hydroformed chamber should work better.

But on a chainsaw they become too big and clumsy for real world cutting.

 

[Chris-PA]

Most chainsaw pipes are multiple cones welded together to approximate the proper chamber.

if you had it all worked out a stamping, or better yet a hydroformed chamber should work better.

But on a chainsaw they become too big and clumsy for real world cutting.

Yeah, pipes for performance are too long to be practical. But keep in mind that these pipes are tuned to have the exhaust pulse go out to the end and get back to the port just in time for the next exhaust port event. The SLR is not trying to do that at all - it is trying to get a reflection back to the port at the end of the same exhaust event in order to prevent fresh mix from leaving the cylinder. That means they want a positive reflection and a much shorter travel time - which is what the SLR chamber looks like to me. Only it still looks like it would be way too short.

 

[sachsmo]

Remember riding 2 smokers as a kid.

Most dudes would go on about the "powerband"

Dad always called it "gettin" on the pipe"

 

[edisto]

Yeah, pipes for performance are too long to be practical. But keep in mind that these pipes are tuned to have the exhaust pulse go out to the end and get back to the port just in time for the next exhaust port event.

No...they are timed so that the impulse from the exhaust opening get back before the exhaust port closes.

 

[Chris-PA]

No...they are timed so that the impulse from the exhaust opening get back before the exhaust port closes.

Understood, which is why a small change in rpm can make such a drastic difference in a tuned pipe engine. But I was really trying to point out the difference in trip length required to get the pulse back for the next exhaust event vs. trying to reflect it back during the same event. The latter requires a much shorter pipe.

 

[edisto]

Understood, which is why a small change in rpm can make such a drastic difference in a tuned pipe engine. But I was really trying to point out the difference in trip length required to get the pulse back for the next exhaust event vs. trying to reflect it back during the same event. The latter requires a much shorter pipe.

Why on Earth would you want to reflect it back for the next "event"? Apart from requiring a longer pipe, you'd have interference between pulses.

Again...they are timed so that the impulse from the exhaust opening gets back before the exhaust port closes.

It's quite possible it could be me, but one (or both) of us is confused.

 

[one.man.band]

Why on Earth would you want to reflect it back for the next "event"? Apart from requiring a longer pipe, you'd have interference between pulses.

Again...they are timed so that the impulse from the exhaust opening gets back before the exhaust port closes.

It's quite possible it could be me, but one (or both) of us is confused.

maybe both of you are trying to word the same thing?
.............................................................................................
tuned pipe formula is based on sonic wave speed (based on temperature, time, and velocity).

gas flow is another animal. based on pressure, temperature and velocity. (Boyle's law). also friction.

the pipe formula is just an approximation using a straight (not curved) pipe to get you close. because most all exhausts need curved pipes, experimenting is still necessary to find the optimum length. because it's gas flow has mass, and slows around curves. the formula does not directly account for this, at least thats the way i see it.

-omb

 

[edisto]

maybe both of you are trying to word the same thing?

Nope. I'm just trying to figure out why he would want to tune for the next cycle.

the pipe formula is just an approximation using a straight (not curved) pipe to get you close. because most all exhausts need curved pipes, experimenting is still necessary to find the optimum length. because it's gas flow has mass, and slows around curves. the formula does not directly account for this, at least thats the way i see it.

The formulae are for the waves, which are more or less indifferent to bends. As you point out, the gasses are not, and too much twisting and turning can generate heat issues.

 

[Chris-PA]

Why on Earth would you want to reflect it back for the next "event"? Apart from requiring a longer pipe, you'd have interference between pulses.

Again...they are timed so that the impulse from the exhaust opening gets back before the exhaust port closes.

It's quite possible it could be me, but one (or both) of us is confused.

LOL - Quite possible, I think I remember being confused once!

My understanding is that you want the pressure pulse to hit the closed exhaust port, reflecting from it just before it opens. That creates a low pressure as the port opens. The only event that can do that is the previous cylinder firing. Also, if the pulse arrived any time the port was open it would cause problems. I'm fairly sure that all intake and exhaust tuning is using the pulses from the previous cylinder firing.

 

[edisto]

My understanding is that you want the pressure pulse to hit the closed exhaust port, reflecting from it just before it opens. That creates a low pressure as the port opens. The only event that can do that is the previous cylinder firing. Also, if the pulse arrived any time the port was open it would cause problems. I'm fairly sure that all intake and exhaust tuning is using the pulses from the previous cylinder firing.

You don't need low pressure when the exhaust opens. There is plenty of pressure in the cylinder.

The opening of the exhaust creates a positive pressure wave. When a wave in a tube leaves that tube, a wave of the opposite sign travels in the opposite direction. This negative pressure wave needs to get to the exhaust port once the big pressure differential is gone to help "pull" more exhaust out, and more charge in to the cylinder.

The wave from an abrupt opening would be strong, but too short in duration. An expanding cone produces the same effect as an abrupt opening, but with less strength and more duration. That is what the first cone in a tuned exhaust is for.

When a pressure wave moving though a pipe hits the closed end of a pipe, a pressure wave of the same sign is reflected back. Again, a cone (in this case constricting) produces the same effect, but with less strength and longer duration. This is what the second cone is for. The reflected positive pressure wave produced by the second cone "chases" the negative wave towards the exhaust port, stuffing back some of the charge that was "pulled" out of the cylinder by the negative pressure wave.

All of this has to happen between the opening of the exhaust port and the closing of the exhaust port.

Check out the gif in post #20 of this thread.