Making Your Own Muffler

[Pete Logan]

Do you have access to any kind of shop where you could fabricate baffle tubes? I know you can buy them, but if you can make things, it will be cheaper.

Quoted from another thread.

In the strange world of coincidence, I'm trying to do just that at the moment, but am having some problems finding information on what's required exactly.

At the moment, I have an outer casing and a straight inner tube with holes in it, but no baffles. This is just the way the bike came from the previous owner.

I would like to keep the outer casing, just for looks.

I have seen one site which says to make a baffle which fills the inner tube, and has a hole in the middle of it (effectively a washer the same size as the inner exhaust tube). They recommend mounting this baffle on a swivel so that it can be turned through 90 degrees and fixed between fully filling the inner tube at one extreme, and being effectively straight through at the other extreme, and then playing with the angle it is set at to get the best compromise between noise and power by road testing.

What they don't answer is:

1. Should the inner tube have holes in it so that the exhaust gases spill out into the outer casing at the baffle, and are then forced back into the inner tube where it joins up with the outer casing at the end, or should it rely solely on the hole in the middle plus the clearance which depends on the angle it is set at ?

2. How far along the inner tube should the baffle be set ? The whole muffler is 24" long. Should the baffle be at the front, the back, or somewhere in between ?

Any help would be greatly appreciated, not least because a replacement is around $450 around here

Thanks.

Pete

[earlfor]

Re: Making Your Own Muffler

Pete, the only internal muffler fabrication I have done was in duplicating to replace something I had that was worn out. Some mufflers have baffles at both ends. In those cases, they usually are offset. The idea being to stop the flow from having a straight path out the exhaust. Some only have a baffle at the outer end. Usually, an end baffle is solid and mounted on a center tube with holes drilled in the center tube. The center tube is then wrapped with a packing. Do you have one good side that you can look at to see the configuration? What bike is it. I may know how the muffler is constructed internally.

Earl

Do you have access to any kind of shop where you could fabricate baffle tubes? I know you can buy them, but if you can make things, it will be cheaper.

Quoted from another thread.

In the strange world of coincidence, I'm trying to do just that at the moment, but am having some problems finding information on what's required exactly.

At the moment, I have an outer casing and a straight inner tube with holes in it, but no baffles. This is just the way the bike came from the previous owner.

I would like to keep the outer casing, just for looks.

I have seen one site which says to make a baffle which fills the inner tube, and has a hole in the middle of it (effectively a washer the same size as the inner exhaust tube). They recommend mounting this baffle on a swivel so that it can be turned through 90 degrees and fixed between fully filling the inner tube at one extreme, and being effectively straight through at the other extreme, and then playing with the angle it is set at to get the best compromise between noise and power by road testing.

What they don't answer is:

1. Should the inner tube have holes in it so that the exhaust gases spill out into the outer casing at the baffle, and are then forced back into the inner tube where it joins up with the outer casing at the end, or should it rely solely on the hole in the middle plus the clearance which depends on the angle it is set at ?

2. How far along the inner tube should the baffle be set ? The whole muffler is 24" long. Should the baffle be at the front, the back, or somewhere in between ?

Any help would be greatly appreciated, not least because a replacement is around $450 around here

Thanks.

Pete

[Pete Logan]

Thanks, Earl. It's a 1980 FLH. 2:1 header with a single (original) fishtail muffler.

As it came to me, the inside tube has holes, and there was a single baffle about four inches from the front of the muffler which had been knocked out by the PO to give a straight through. There is no packing in there, I don't know whether there would have been originally or not.

What I'm planning on doing is to set the outer casing up so that the inner tube is held in with a single nut/bolt at the rear. In this way I can build a number of different inner configurations to compare how they work for noise and perceived performance.

At the moment I have it set up with a single baffle about halfway along the muffler, which is on a 90 degree swivel so I can turn it to be straight through, completely block the tube, or anywhere in between. This baffle is solid (no hole in the middle) and completely fills the inner tube.

As you would expect, if it is set closed, the noise comes right down, but the performance is totally killed. Wide open and I get both performance and maximum noise. Halfway between seems to be not too bad either way, but I'm hunting for a noise meter to get a better idea.

I'm pretty sure it should have at least a small hole in the middle, and I'm pretty sure that halfway along the muffler is the wrong place, but I'm not sure where to go from here, except just to build as many different setups as I can think of and try them all out.

Only problem is I need to get the bike through technical inspection before I can use the road, so I need an initial setup that is as quiet as possible.

It's worth a little experimenting, 'cos if I have to buy a muffler, that's gonna be $250 around here

Thanks.

Pete

[earlfor]

Pete, I've never had a HD pipe apart, but what I have found to work with a minimum of refabrication is to use aprox an 18" long, 1" diameter tube. Weld a baffle at the rear that blocks the muffler end completely,but leaves the tube open so the only flow is through the tube. Crush/close the inboard end of the tube. Then drill 1/4" holes along the length of the tube. I usually drill enough holes to equal about 1 1/2 times whatever the open end of the muffler would be. This will give you plenty of flow capability and the crushed end of the pipe does not allow the exhaust a straight out flow, which helps to make it a bit more quiet. Then to "adjust" the noise/flow, I wrap the tube in fiberglass woven roving. Just the bare glass roving. Roving is a coarse, heavy, loose weave, cloth like material. Usually about 6 or 8 layers is sufficient. Secure it with a wrap of baling wire ever couple inches. You can adjust by changing the number of wraps of roving around the pipe. Put a tab on the end bracket so you can bolt it in place in the muffler shell.

Earl

I'm pretty sure it should have at least a small hole in the middle, and I'm pretty sure that halfway along the muffler is the wrong place, but I'm not sure where to go from here, except just to build as many different setups as I can think of and try them all out.

Only problem is I need to get the bike through technical inspection before I can use the road, so I need an initial setup that is as quiet as possible.

It's worth a little experimenting, 'cos if I have to buy a muffler, that's gonna be $250 around here

Thanks.

Pete

[Pete Logan]

So release the exhaust gas into the larger space as soon as possible (in itself a noise reducer), and then let it find it's way back into the central tube through an adjustable amount of further noise reducing material. (Just rephrasing to check I got the principle right.)

That sounds very logical and practical, Earl, thanks a lot. I'll go put it on my list of 'things to do'

Thanks again for your help.

Pete

[Anonymous]

I bought a set of univeral mufflers via ebay a month ago, they made all the back pressure by throwing all the exhaust out a 3/4in hole, that that made it sound like a little 5 hp briggs IMO. So with my understanding of mufflers in 4-wheelers (I've tried out a few combo's on my wheeler). So with the megaphone styling, I bought the steel with holes in them from a guy I know, and hand bent it into a tube with the diameter about 1 1/2". then welded it together, and welded 2 washers in the tube, 1 about 1/3rd way and 1 about 2/3rds the way. This is the key for backpressure but retaining a nice low tone grunt. the inner diameter of the washers was about 1/2". This makes the exhaust want to go around the washer(also does quite a bit of quieting) and then I fitted the old encap on there after drilling it a larger diameter. I will get pictures today.-darren

[earlfor]

You got it in a nutshell Pete. :-)

Earl

So release the exhaust gas into the larger space as soon as possible (in itself a noise reducer), and then let it find it's way back into the central tube through an adjustable amount of further noise reducing material. (Just rephrasing to check I got the principle right.)

That sounds very logical and practical, Earl, thanks a lot. I'll go put it on my list of 'things to do'

Thanks again for your help.

Pete

[Anonymous]

http://image48.webshots.com/49/5/90/84/298259084ktDxtJ_ph.jpg

http://image32.webshots.com/32/5/91/83/298259183LkZHhu_ph.jpg

I might end up making the washer inside diameter bigger but I would rather start with a little too much back pressure and being a little rich then not enough and burning an exhaust valve and being lean.-darren

[Pete Logan]

Thanks guys. I'll give it a couple tries and see how we go.

Darren, I get Access Forbidden on those pictures.

Pete