muffler mod engineering?

[T0RN4D0]

There is no serious science in these kind of mufflers. They are there to reduce noise levels, and manage heat/fire issues of exhaust gasses.

The truth is it doesn't matter much how many holes and in which places you make, you aren't going to achieve anything (past "letting it breathe, exchanging some minor gains in return for more noise) until you properly pipe it. One hole, two holes, 10 holes, weld a 2" pipe to it, any kind of deflector, it won't make any real difference.

Size of the muffler is probably designed by how much space they have left. The bigger the better, as it helps cool down the gases some, would be my guess.

 

[bikesandcars]

Hey, if it was easy everyone would do it (or someone would at least provide a solution). Lets keep the thread focused on positive engineering discussion (i.e. thoughts / links towards the OP goal).

Work through this with me: A typical box muffler with a small opening at the top will still reflect back a pressure wave, under the simple concept of it hitting the front wall and returning to the piston it arrives at the piston too early and too weak (unfocused) to do anything useful like forcing the intake charge to stay above the piston in a tuned exhaust. So lets remove that from the equation for a thought exercise. If you take the scavenging efficiency out the remaining power-adder is simply removing the exhaust backpressure.. simple engine stuff......but people report that if a hole is too big it destroys the powerband and the saw runs worse... also.. if that was productive someone would have used a megaphone exhaust by now. So taking the above together.. obviously the "box" is having some positive effect on the efficiency / scavenging of the engine..and there is a certain sweet-spot of backpressure. so there must be a simple way to explain it at a high level (and of course a hard way to explain it with a mathmatical model).

 

[ncfarmboy]

Measure ex. port inside cylinder vert. and horizontal do the math. LxWx.85 is usually the best all around ex. opening no spark screen. With screen LxWx100. WP and stock. If you use a spark screen don't forget the opening size of screen. Is oil thread next? :deadhorse:
Shep

 

[UK Rich]

Whats peoples thoughts on outlet placement? Any back to back research? On the side, the top, bottom? Front cover or make the waves hit the front cover and come out the back? I'm guessing opposite the ex. port is a bad idea - low back pressure.

Multiple holes, one large or tube?

 

[Festus]

I know this has all been more or less stated in this thread already, but more simply put, the engineers are trying to balance the priorities of air flow, noise level, weight, size, cost, esthetics, and serviceability when they design a muffler. Anything we do to modify a muffler is simply adjusting the balance of these priorities. Namely accepting more noise because we want MORE POWER.

 

[parrisw]

I like tubes, a single 1" sounds great on a 372.

 

[blsnelling]

I like tubes, a single 1" sounds great on a 372.

Is there such of a thing as a 372 that doesn't sound awesome

 

[parrisw]

Is there such of a thing as a 372 that doesn't sound awesome

No, but I find a big difference, I have two runners now, one with the single 1" outlet, and 1 with a very large factory style deflector. The one with a tube sounds more "HOT ROD'ISH"

 

[timbrjackrussel]

Two-Stroke Tuners Handbook G. Jennings
http://edj.net/2stroke/jennings/2stroketunershandbook.pdf

 

[openloop]

I think the OP is attempting to treat the simple muffler on a saw as a tuned exhaust like a pipe would be.... The truth is a stock muffler will NEVER give you the advantages of wave tuning. Its simply too small of a chamber with too many chaotic reflections. Its sole purpose in life is to quiet the exhaust. The sole purpose of a tuned pipe is too increase reflections (noise) and use them to push back fuel/air that has made it out of the exhaust on the compression stroke. The two in reality are not compatible. The best we can get out of a stock muffler is to simply allow it to flow gases with as little restriction as possible.... much the same way putting a less restrictive muffler on your car could increase power simply by allowing the car engine to breath.

If you are looking to harness reflected waves to cram fuel/air back into the cylinder just before the exhaust port closes you are barking up the wrong tree. The tree you would be looking for would be a tuned pipe with divergent and convergent cones.

 

[tolman_paul]

It's difficult to have an engineering discussion because there aren't that many engineers on the forum, and no offense but it seems some people have the mindset that makes more noise must mean makes more power. It's rare to see any sort of statistically relevant comparision of various mods, and I don't think I've ever seen dyno runs made on the engines.

There really needs to be two discussions. One from the point of view of an accoustical engineer to discuss the effects of the muffler design on noise reduction, and then another discussion of the effects of design on engine performance, both positive and negative effects.

As to why an port makes less power than a muffler, the open port allows part of the air/fuel charge to be lost out of the exhaust port. Some amount of back pressure is needed to keep that air/fuel charge in the engine, but too much back pressure restricts the engines ability to pump air through it.

To me a statistically relevent test would require an engine with head and exhaust temp gauges, a comparison of muffler volume to engine displacement dyno runs comparing different exhaust port configurations and dB readings to see the effects of exhaust configurations on sound levels.

 

[Festus]

Does a 12 gauge shotgun barrel count as a tube. It sounds pretty hotroddish.
The kid blew up his ventilated rib barrel a few years ago. I made use of it.
Hope this shows up. Never posted a picture before.
View attachment 261045

 

[3000 FPS]

I prefer double barrel shotguns myself.

View attachment 261046

 

[Festus]

I prefer double barrel shotguns myself.

The kid only blew up an 870 Remington.
And how do you aim it without the sight bead.

 

[WidowMaker1]

Ha I got a Big long one ...

 

[Festus]

You know, one of them college edumacated engineers of scientists would never come up with stuff this cool.

 

[tigerrider11]

Perhaps we can add some technology to the field of Muffler Mods...
Yes, we can remove flow restrictions, open up exhaust vents (but not too much to reduce the needed back pressure) and so on hoping to obtain satisfactory results for our work. We can even utilize fancy screens, welding, paint jobs, extra ports, etc... but until actual experiments with documented results are done, along with a control, we are all just suffering from what may be more or less a placebo after a certain extent.
Now, with that said, an experiment doesn't have to entail buying countless mufflers in order to vary each one slightly in order to get real world data. It can be, as mentioned before, done with advanced CFD software.
Now everyone doesn't have access to a software like Ansys, know in-depth Navier-Stokes theory, or understand the difference between some simple concepts such as laminar or turbulent flow, boundary conditions, and so on.
However; some of us do, or at least did (College)...

What would be interesting is to develop accurate muffler geometrical meshes, apply boundary conditions, and let the computer run the simulations... we could manipulate the port area, location, number of ports, baffling, shape, and so on and actually obtain real (on the computer) numbers.

It may also give us a look at what may be bad for "flow" such as vena contracta, stagnant regions, and dangerously turbulent regions (over time) and so on...

Unfortunately, for those without access to graphical interface simulation programs such as Ansys FLUENT, our choices are the more object oriented language programming based simulators such as OpenFOAM. Because of the steep learning curve involved with object oriented programming, unfortunately the world of muffler modding will remain less of a science and more of an art.

And with any form of art, there will always be good artists

 

[GBD]

I like tubes, a single 1" sounds great on a 372.

Make it around 14 inches long from piston

 

[3000 FPS]

Perhaps we can add some technology to the field of Muffler Mods...
Yes, we can remove flow restrictions, open up exhaust vents (but not too much to reduce the needed back pressure) and so on hoping to obtain satisfactory results for our work. We can even utilize fancy screens, welding, paint jobs, extra ports, etc... but until actual experiments with documented results are done, along with a control, we are all just suffering from what may be more or less a placebo after a certain extent.
Now, with that said, an experiment doesn't have to entail buying countless mufflers in order to vary each one slightly in order to get real world data. It can be, as mentioned before, done with advanced CFD software.
Now everyone doesn't have access to a software like Ansys, know in-depth Navier-Stokes theory, or understand the difference between some simple concepts such as laminar or turbulent flow, boundary conditions, and so on.
However; some of us do, or at least did (College)...

What would be interesting is to develop accurate muffler geometrical meshes, apply boundary conditions, and let the computer run the simulations... we could manipulate the port area, location, number of ports, baffling, shape, and so on and actually obtain real (on the computer) numbers.

It may also give us a look at what may be bad for "flow" such as vena contracta, stagnant regions, and dangerously turbulent regions (over time) and so on...

Unfortunately, for those without access to graphical interface simulation programs such as Ansys FLUENT, our choices are the more object oriented language programming based simulators such as OpenFOAM. Because of the steep learning curve involved with object oriented programming, unfortunately the world of muffler modding will remain less of a science and more of an art.

And with any form of art, there will always be good artists

At the beginning of this thread, there is a reference with a link to what Timberwolf did with a documented, scientific, controlled example of what happens when you open a muffler up for better flow. I can tell some of you did not bother to read it.

 

[tigerrider11]

At the beginning of this thread, there is a reference with a link to what Timberwolf did with a documented, scientific, controlled example of what happens when you open a muffler up for better flow. I can tell some of you did not bother to read it.

The thread is muffler mod engineering, and yes while TimberWolf did do some great experimentation that led him to some hypotheses that could indeed aid in the design of a muffler that needed to flow like (a), and have fuel consumption like (b) and be able to cut (c) fast...all the while agreeing with some before thought out numerical area ratios, there are other options/validations out there.

My post was to show that we can experiment with much more variables and actually see (depending on the mesh and conditions) what's going on inside the muffler when these variables are well, varied; in a much shorter amount of time. TimberWolf would have to go through much more metal, cutting, welding, fuel, testing, ect in order to physically model different muffler aspects.

I am in no way saying what TimberWolf did was inferior, as I also believe that desk jockey engineering is not enough and experience cannot be replaced by textbooks... I was just shedding some light on the fact that some things might be pretty interesting from the stand point of engineering such as: what mach number the exhaust gasses reach and where, or even something simple like a pressure map of the muffler can. You know, some of the more "not so useful" tidbits that our minds feed off of.

Anyways, being partial to CFD I just think it would be cool to see what some flow charactistics looked like when properly modeled.