DIY muffler design?

Long story short - I want a free-flowing exhaust for my diesel E350 van. I can buy one for $380, or I could just buy the 4" downpipe and have my buddy make up a cheap 4" exhaust for it. I don't mind the straight-pipe sound, but I'm a bit afraid of noise/drone inside a large van. Buying a performance muffler kinda kills the low-budget aspect.

Which made me think about using some steel I have to weld up my own muffler.

Any links or tech I can glean from you guys/gals about building my own muffler? Maybe some info on how different designs alter the sound waves? Most of my muffler design knowledge is limited to how a flowmaster 3-chamber compares to a glasspack, or how a Dynomax compares to Borla sound.

Basically, I want a big, free-flowing muffler that acts as a resonator to help reduce the possibility of interior drone. Ideas?

I would suggest you include the term "FSAE" in your search for muffler design. Lots of student have asked the exact same question, but for smaller scale flow.

I think there is a muffler build/ design of a twin loop muffler on hondatech in the fab section that might give you an idea or two.

I buy personally whatever the longest cheapest straight mufflers (search resonator at the site for more results) that I can fit at summitracing. I can get two or three under small cars and they do a good job of keeping noise down, flow well and are lighter than the factory oh and they are cheap ( under $30 last I checked.)

I have thaught of this as well and design is as follows.

Get a piece of steel exhaust tube say 2.25 OD Cut slots in it about 1" long across the pipe about 1" apart around the pipe staggered from one another, take a ball peen hammer and dent one side of the slot in to the pipe being consistent with the side you bend in on all the slots. Take stainless steel expanded wire mesh (the stuff used for lath and plaster) and wrap around the pipe until it is about 3/4" thick. Leaving about 3" of the pipe exposed on each end Go get another piece of pipe that will slip over the pipe you have wrapped with the mesh that is the same length of the inner pipe and cut slots in the ends the ends about 2-3" up the pipe. Slide the wrapped pipe in the larger one and bend the tabs at the ends down and weld to the inner pipe and weld the slots closed.

What I don't know is what direction to mount it in do you want the dented in tangs with the flow or against the flow?

I love making stuff. It's why I have a machine + fab shop. That said, my time is worth something.

I'll make exhaust systems - headers even - out of commercially available components. Making mufflers, when Summit lists 7200 part numbers seems like less than the best use of life.

4" in and out, pretty huge, under $60

I had a square tube 8x8 in welded into my diesel exhaust about 3ft long.... I don't see why you could shorten the same tubing and weld in a few angled plates to cut down drone.

Whenever I have to drive a vehicle straight piped for a while I have a homemade little rig I make up using packed steel wool and screen door mesh. Obviously the steel wool is (A flammable, not in a low oxygen atmosphere) and (B door mesh is extremely prone to burnout and rust) but I see no reason a heavier wire or perforated steel plate wouldnt act as a free flowing sound deadener in a chambered exhaust.

motomoron wrote: I love making stuff. It's why I have a machine + fab shop. That said, my time is worth something. I'll make exhaust systems - headers even - out of commercially available components. Making mufflers, when Summit lists 7200 part numbers seems like less than the best use of life. 4" in and out, pretty huge, under $60

You're right that is cheap. I'll have to look for some flow numbers on it.

I wish I could find a link to them, but I was also thinking about those perforated cones that you can put in header collectors. One of those in the inlet and outlet of a steel box might do the trick.

In reply to dean1484:

You don't want the perforations to interfere with the flow that would mean a good amount more restriction. Like putting in a louvered core muffler in backwards, a big no no.

Just like cutting slots one could drill larger holes, might be less work. They sell replacement muffler stuffing, I would be temped to use pink panther house insulation wrapped thick and packed down with that mesh. Some of it would burn up after a while but it's next to free.

With regards to drone, there's a way to fix that, http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

In my experience from FSAE a number of years back, even with solid research building your own muffler design can be hit or miss if you're not just copying an existing design...In which case you'll probably come out ahead on time and/or money by just buying the existing mass manufactured design. Generally speaking, the greater the muffler volume and the smaller the inlet/outlet in proportion to the muffler body, the more muffling potential it has.

In reply to bgkast:

Already has one of those

I guess I could add another

The other thing I thought of is I could go with a straight exhaust (no muffler) and modify it later if it drones too much.

I drove a straight piped diesel Dodge truck for four hundred miles one day. I didn't find it to have excessive drone.

bgkast wrote:

Hah, I've got one of those as well. I tried it with a straight pipe and it's almost quite enough for the street, but took it off to avoid unwanted attention.

Driven5 wrote: In my experience from FSAE a number of years back, even with solid research building your own muffler design can be hit or miss if you're not just copying an existing design...In which case you'll probably come out ahead on time and/or money by just buying the existing mass manufactured design. Generally speaking, the greater the muffler volume and the smaller the inlet/outlet in proportion to the muffler body, the more muffling potential it has.

I worked the course af FSAE West one year and there was a car that was way-loud. I asked around how the devil they got past the noise test, and I had to tip my hat at what they did. They knew the rpm at which the test was run, and that was that... they designed a resonant "muffler" which worked great... at that one rpm. They passed legally....

The other "flexible design" was one that after a couple laps, spit its stuffing out the tailpipe. "Oops..."

Yes, I can safely say our car sounded like nothing else out on the track. There are a number of tricks that can be used when one knows the specific rpm for attenuation. A muffler for a street car can also focus primarily on a target RPM band using some of the same concepts. However to get enough noise attenuation, while not inhibiting airflow, and while keeping the muffler body compact, is still a surprising challenge.

The Donaldson mufflers seem to be pretty popular on the diesel forums.

http://www.ryderfleetproducts.com/donaldson-m085171/muffler-4-in-4--out-p-w26-m085171

P.S. I have a 7.3 powered Excursion with a straight exhaust. I was talked into it by the shop that sold me the exhaust, even though I wanted a muffler. I haven't gotten around to putting a muffler on mine yet, but you will want it. Especially towing, and especially around 1750 RPM, when the drone will make you want to punch the guy that talked you into skipping a muffler in the face.