muffler mod engineering?

[parrisw]

Make it around 14 inches long from piston

Hmm

 

[parrisw]

HOLY CRAP, its just a muffler people!!!!!!

 

[parrisw]

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.

You should do that and let us know how it works out.

I'm just going to keep sticking big holes in them.

 

[parrisw]

There has been many many test's on this site on what muffler mods will do. Sometimes you can expect up to 20% gains, and even more in some real choked up saws.

 

[WidowMaker1]

HOLY CRAP, its just a muffler people!!!!!!

dont be like that. come on we all know when we take a hit from the bong ,the bigger the cone the bigger the giggle

 

[Andyshine77]

There has been many many test's on this site on what muffler mods will do. Sometimes you can expect up to 20% gains, and even more in some real choked up saws.

We have quite a few variables, the saws design, the mufflers design, the shape volume and so on. Honestly most of this only becomes a big factor when you get into scavenging. I know of maybe two saws with stock mufflers that seem/are designed to do this, the 7900 and 7910. With that said we're still not talking about tuned pipes.

 

[boca joe]

Is that your hot air I'm feeling on my neck, your smoke obscuring my vision or just your hollow words I'm hearing?

I guess I'm not buying what most of you clowns are selling because I can get all I need for free from the nearest cow pasture.

Talk is cheap; actions are dear. TW did the work and you guys are just trying to blow sunshine up my rear, but it isn't gonna work 'cause I was building a Fortune 500 when many of you weren't even a gleam in your daddy's eye. LOL.

Bottom line: Do what Snell told you at the start - Open her up a bit and let 'er rip.

 

[bikesandcars]

Comeon fellas...i started this thread to have a different type of muffler discussion, not the same muffler discussion again.

TW did great work and im still catching up with many of his posts.

Thanks for the feedback but "hog her and rip her" and "its too hard to possibly understand" type posts have been extensively covered, hoping to do something better

 

[openloop]

Comeon fellas...i started this thread to have a different type of muffler discussion, not the same muffler discussion again.

TW did great work and im still catching up with many of his posts.

Thanks for the feedback but "hog her and rip her" and "its too hard to possibly understand" type posts have been extensively covered, hoping to do something better

How much more of a discussion would you like to have about a small metal box with a few holes in it?

 

[borat]

"Anal retentiveness

The term anal-retentive (also anally retentive), commonly abbreviated to anal,[1] is used conversationally to describe a person who pays such attention to detail that the obsession becomes an annoyance to others, potentially to the detriment of the anal-retentive person."

Anyone detecting symptoms of the above?

 

[dl5205]

Stihl only "mildly" entertaining thus far....

 

[Gologit]

opcorn:

 

[Trx250r180]

a lot of the fallers around here ,go for the dual port cover on the stihls ,then drill a 1/2 inch hole on lh side and add a 3rd port and put a husky deflector and a screen over the 1/2 inch hole

 

[tolman_paul]

Comeon fellas...i started this thread to have a different type of muffler discussion, not the same muffler discussion again.

TW did great work and im still catching up with many of his posts.

Thanks for the feedback but "hog her and rip her" and "its too hard to possibly understand" type posts have been extensively covered, hoping to do something better

This is simply the wrong forum to have that type of discussion. Unfortunately I think the type of forums where you could have a thoughtful discussion on the subject are forums where people are tuning engines using tuned pipes. It would be interesting to bend the ears of the muffler designers for the various saw companies, I'm sure they have some ideas that while not practical for a commercially produced saw would provide some benefits.

My gut tells me there just aren't going to be significant power gains over the open er up and let er rip approach. To further complicate things you can't model the muffler based on how it behaves during steady state flow, i.e. a flow bench because you are dealing with a high frequency pulse.

What I would personally like to see is some studies to compare engine displacement to muffler volume and exhaust port area to muffler discharge area and including dB loss. I value my ears and there is no reason you can't gain some power while simultaneously dropping engine noise.

I also would like to see some work done on for lack of a better description a conch shell type muffler where the exhaust gasses are directed out towards the front of the muffler, turned down to the bottom, then back up and then out the side. Think of it as a mini megaphone with slight gains from it being a diffuser but more importantly a more directional control of the flow of the exhaust gasses.

 

[tigerrider11]

Just to show some simple and quick 2d calculations using a 0.6" inlet and a 0.75" outlet, and a very simple representation of a muffler.
the first picture is the pressure contour... someone correct me if i'm wrong, but i think i recall a lower pressure drop = more flow (ie more velocity)
there are areas of low and high pressure...most notable is the highest pressure right above the outlet (which may be drastically reduced if there was a radius on that corner)

View attachment 261222

Next is the velocity vector profile, notice the correlation between the two images. the vectors are most helpful in showing the air's path through the can.
The calculations were done using the mass flow rate of air exiting the cylinder of an 026 operating at 10,500 rpms.. (0.0104400625 kg/s).

View attachment 261223

Kinda fun i guess to see inside of what's going on. Im sure there are much more accurate ways to model this, i only did this very quickly.
It may be possible to "reenact" TimberWolf's experiment just to validate the computer results...
is this very useful? probably not unless you work for a chainsaw company...
I personally still like the idea of going a little at a time to notice the changes and learn that way

 

[WidowMaker1]

 

[SawTroll]

Hmm

Sounds like a "shortpipe" muffler to me - lots of work to make within the size of the original muffler - if possible at all......:msp_wink:

 

[SawTroll]

We have quite a few variables, the saws design, the mufflers design, the shape volume and so on. Honestly most of this only becomes a big factor when you get into scavenging. I know of maybe two saws with stock mufflers that seem/are designed to do this, the 7900 and 7910. With that said we're still not talking about tuned pipes.

The carb venturi and the capasity of the transfers are other variables (important ones). :msp_wink:

 

[greg409]

"Anal retentiveness

The term anal-retentive (also anally retentive), commonly abbreviated to anal,[1] is used conversationally to describe a person who pays such attention to detail that the obsession becomes an annoyance to others, potentially to the detriment of the anal-retentive person."

Anyone detecting symptoms of the above?

B - you could have at least combed yer hair - Put your girl back up please

luck,greg

 

[lambs]

As I read all this, I guess I'm wondering what the point is of all this. There are lots of mufflers out there of various designs, so it seems to me even if we figured out the perfect mod it would only be perfect for one muffler design for one model of saw. So it seems to me if you want to mod yours, you can probably figure the rule of thumb that others have developed not with engineering but with observation is about right and will probably get 80% of the benefit possible with almost no effort.

Not trying to rain on anyone's parade here, just adding my thoughts.