Quote from: quiktaco on March 26, 2008, 07:19:32 PM
No, haven't tuned two stokes.  I've studied up on muffler design, and diffusing the gasses/soundwaves, then letting them expand slightly, then forcing them into a smaller opening again tames the noise level and increases backpressure.  An expansion chamber in a 2 stroke is a lot larger than what I have here, and are generally used to increase low end torque if I'm not mistaken.  Thanks for the input.  I was thinking about ditching the idea of diffusing it, but figured I might as well, cause I want it as quiet as possible.

~~

Oh, and the 3/4 inch outlet is because I'm cutting away about 2 feet of pipe that the gasses would normally travel through, so I figure a smaller diameter outlet will increase backpressure some.

You're going about it all wrong.  If you're wanting it to be quiet, don't change it.  Just leave it alone.  What you have pictured here will do nothing for noise control.  Actually, moving the muffler closer to the engine, reducing muffler volume, and cinching it all down to a 3/4" outlet will do nothing but give you a raspy lawnmower that is anything but quiet.

Here's two big things you need to keep in mind when building an exhaust:

When it comes to using a muffler to control the noise of a motor, the only truly effective device is volume.  That's right...the bigger the muffler is, the lower the pitch will be, the more controlled the flow will be, and the quieter the exhaust note will be.  You want it quiet?  You need to think bigger or far, far more complex.

Forget everything you think you know about back-pressure because, surprisingly, even the people who think they've researched it thoroughly can't seem to grasp the concept that it's so variable as to almost be 100% pointless to even take into consideration.  Any exhaust you make will work in a specific rpm range, and absolutely no exhaust you can make will work adequately throughout the entire rpm field.  An exhaust is all about the volume of gases moved and where you want the most noticeable power at.  Sticking a 3/4 nozzle on the end of that thing will bottom out your powerband and you'll have to drop your jetting and get colder plugs just to keep from caking your valves with soot and carbon.

Thanks for the insight.  I guess I did have the idea of backpressure incorrect...at least on the side that it can be compensated for with bigger jets.  I know doing this is going to make it louder.  If it's too loud then I'll weld the stocker back on and come up with another idea.  The stock inner diameter of the outlet pipe is the same size as what I will be using, so it can't chock the engine any more than the stock muffler does, so I'm not too worried about that.

Have you seen the inside of a stock GS500 muffler?  I guarantee you it's not 3/4" tubing and the outlet is closer to 1.5".  The stock muffler uses a smaller can with a complex multi-chamber design that effectively increases the relative volume of the can.

Keep in mind that it is NOT the diameter of the tubing alone that decides flow.  You can have four ince tubing but if you choke it down to 3/4" at the end you may as well have the whole thing 3/4".  Plus, it's not just the outlet...the core you're making is 3/4".  That means that the effective inner diameter of the muffler is 3/4"...which is much more restrictive than the stock tubing.

No, never seen the inside of the stock muffler.  I know for a fact though, that the outlet of my stock gs is the same as what I got.  Mine is a 96 if that makes any difference.  Maybe the newer ones are larger.

Given these outside dimensions of 2.5" by about 11-12", how would you design the inside?

And also, if you were given a project that at least had to have the illusion of this small of muffler, what would some ideas be?  a box muffler under the frame?  2 separate, baffle only mufflers for each cylinder?  I'd really like to keep the plans going with the original size that I intended, so I'd prefer some insight to how you might build the innerds given those dimensions.

Quote from: makenzie71 on March 26, 2008, 09:41:02 PM
Have you seen the inside of a stock GS500 muffler?  I guarantee you it's not 3/4" tubing and the outlet is closer to 1.5".  The stock muffler uses a smaller can with a complex multi-chamber design that effectively increases the relative volume of the can.

You are saying things that are very contradictory to me.  You are saying that it's closer to 1.5" than to 3/4".  The actual measurement (made 30 seconds ago) is 7/8".  That's what I thought it was.

Quote from: makenzie71 on March 26, 2008, 09:41:02 PM
Keep in mind that it is NOT the diameter of the tubing alone that decides flow.  You can have four ince tubing but if you choke it down to 3/4" at the end you may as well have the whole thing 3/4".  Plus, it's not just the outlet...the core you're making is 3/4".  That means that the effective inner diameter of the muffler is 3/4"...which is much more restrictive than the stock tubing.

  You also say that if the choke down point is a certain size, then you may as well have the whole thing that size.  So the whole stock exhaust (by your logic, which I'm not saying is incorrect) might as well be 7/8" tubing.  Also you say that it is a complex multi chamber exhaust, but I was able to stick a smaller diameter tube 11" into the end of the stock exhaust without restriction.  I'm not saying it isn't a complex, multichamber design, but the last 11" is 7/8" tubing.

Also the exact measurement of the tubing I have purchased for my exhaust is 13/16" inside diameter which is 1/16" less than stock.  I'd say that is fairly negligable.

I like constructive criticism, and I would love it if you could shoot down everything that I just said, somehow.  But you are starting to attack, and not give suggestions to help me with this project.

Read this   

That looks like a good read.  I'm thinking about getting that.

So what's the consensus?  Do you guys think I should use a larger baffle tube?  Should I scrap the whole project and redesign from scratch with a bigger volume canister in mind?

Quote from: quiktaco on March 27, 2008, 07:49:02 AM
You are saying things that are very contradictory to me.  You are saying that it's closer to 1.5" than to 3/4".  The actual measurement (made 30 seconds ago) is 7/8".  That's what I thought it was.

You also say that if the choke down point is a certain size, then you may as well have the whole thing that size.  So the whole stock exhaust (by your logic, which I'm not saying is incorrect) might as well be 7/8" tubing.  Also you say that it is a complex multi chamber exhaust, but I was able to stick a smaller diameter tube 11" into the end of the stock exhaust without restriction.  I'm not saying it isn't a complex, multichamber design, but the last 11" is 7/8" tubing.

Also the exact measurement of the tubing I have purchased for my exhaust is 13/16" inside diameter which is 1/16" less than stock.  I'd say that is fairly negligable.

I like constructive criticism, and I would love it if you could shoot down everything that I just said, somehow.  But you are starting to attack, and not give suggestions to help me with this project.

The last can I cut apart had an outlet of 1.13"~1.25" and it was a manufactured outlet.  I've seen very few and only ever paid attention to one.

Yes, the effective diameter of the stock GS exhaust would be approximately (if your measurement was accurate) .875".  Keep in mind that the stock exhaust is designed for noise control and nothing else.  The muffler on the GS is designed to cut noise by restricting gas flow and creating a large expansion area.  Expansion chambers are used on 4-stroke exhausts but it's an entirely different system than the huge pipes found on four-strokes.  But that's TWO things the GS is using and those two things MUST BE USED in order to keep stock-like noise levels.  The new muffler will have to be multi-chambered with approximately 4-liters in capacity and have a 7/8" outlet...on top of that you'll also have to conjure up a way to add the runner tubing back that you're removing.

It's hard for me to give you suggestions for your project because your goals aren't realistic.  To keep the bike quiet, you'll need a large muffler....and you just won't be able to put one under the bike since there's no clearance.  To keep the look you're going for the bike is going to be loud with absolutely no other gain...probably losses, though.

Volume (as in sound), appearance, performance...you can only control one.

Thanks man, sorry about all the back and forth.  I know that the sound level will be louder.  I know it's not possible to retain the low sound levels of the stock exhaust with a significantly small can.  The main thing this project is for is looks.  I hate the look of the huge stocker hanging of the back.  I know that's what mufflers look like, but I'm going to try it out and see if I can come up with something that will suit me needs.  If it does go louder, that's fine, If it's way too loud, then the stock exhaust will be welded back on until I can think of some other way to get what I want.  It's cheap and should be a fairly easy project, so I figured I might as well try it out.  BTW, my measurements were exact...I have a caliper that measures the inside or outside down to 1/64".

I don't really care about performance either.  As long as it runs well.  If I loose a little power it's no big loss.  I'm not a racer, just use it for commuting a short distance mostly.  If it makes it un-ridable or unreliable, then that's another reason that I would weld the stock can back on.  This is mostly just an experiment, and I thought I'd share with the other gs'ers

Why not go for something like this? - seems to fit the bill for an exhaust that looks slim...



(click for larger pic)

Quote from: quiktaco on March 27, 2008, 10:50:29 AM
That looks like a good read.  I'm thinking about getting that.

So what's the consensus?  Do you guys think I should use a larger baffle tube?  Should I scrap the whole project and redesign from scratch with a bigger volume canister in mind?

no no no ! don't scrap the project ! this is how you and everyone else can learn ! if it's not what you wanted, maybe someone else will want your trash. (one mans trash...)

it's a learning process. you're making stuff for your bike with your own hands. that's got cool points man, major cool points.

take the advice, try a design, try try again. innovate !

That's a pretty slick setup there, philward...but you have to direct the flow away from your rear tire.  Always keep that in mind.

philward, what kind of mufflers are those

Philward,

Where did you get the "S" side cover things. Mine got all scratched up and would love to replace it with one with a blue "s" on the side!

Mary S.

Hold your horses - they aren't mine!  Just food for thought from the forums...

I assume they were made from some muffler extrusions and some premade CF cylindrical stock.    Looks like a pretty straightforward construction.

Quote from: Toogoofy317 on March 27, 2008, 08:13:47 PM
Philward,

Where did you get the "S" side cover things. Mine got all scratched up and would love to replace it with one with a blue "s" on the side!

Mary S.

A member made those and had them for sale, but that was several years ago.

Quote from: Toogoofy317 on March 27, 2008, 08:13:47 PM
Philward,

Where did you get the "S" side cover things. Mine got all scratched up and would love to replace it with one with a blue "s" on the side!

Mary S.

Like this? http://gstwins.com/gsboard/index.php?topic=40228.0

The project is still going.  I think I'm going to make it a bit longer to give more volume to the can size.  The baffle is removable, so I'll be able to up the size or modify it after it's all said and done.

I saw that double muffler setup a while ago, but could find any premade mufflers that would fit.  That might be a great route to take if this idea doesn't work.  That would nearly double the size of the effective muffler space.

Quote from: ben2go on March 26, 2008, 07:09:01 PM
Have you tuned a lot of 2 strokes?4 stroke engines don't use expansion chambers.3/4 inch outlet?A flow thru slip on is 1 and 1/8 to 2 and 1/4.Find a dyno when you're dun.Maybe you're onto something. 

the v&h muffler i have has an expansion chamber in it