Build your own muffler

[Chris Boyden]

Has anybody built their own glasspack style
muffler?

I wish that we had built our own, with a replaceable tip that would allow you to "tune" for sound level. I found some companies that sell perforated stainless tube, which simplifies having to roll your own out of perf sheet. But I haven't priced it yet.

It seems that a well designed exhaust restrictor could really reduce sound while keeping the backpressure as low as possible.

It's a topic that it seems like a lot of teams stuggle with, but it is kinda of black magic when it comes down to designing for the sound requirement. Any ideas?

[Chris Boyden]

Has anybody built their own glasspack style
muffler?

I wish that we had built our own, with a replaceable tip that would allow you to "tune" for sound level. I found some companies that sell perforated stainless tube, which simplifies having to roll your own out of perf sheet. But I haven't priced it yet.

It seems that a well designed exhaust restrictor could really reduce sound while keeping the backpressure as low as possible.

It's a topic that it seems like a lot of teams stuggle with, but it is kinda of black magic when it comes down to designing for the sound requirement. Any ideas?

[bigtoyota9]

For the past two years we have built our own mufflers. Last year I was in charge of building the muffler for the car, I built 3 prototypes using different techniques trying to get the car quite enough, none of them worked. After getting really pissed off what we finally settled on was to copy the internals of a Stock CBR F4i pipe. We changed some stuff around to get a lower profile since it went under our A-arm in the rear. Both years we have rang in at exactly 110 dBa. I was able to reduce the wieght this year a good bit by having a completely aluminum muffler. Including all of the internal baffles and perforated sheet. I think all in all the muffler costed about 35 bucks in materials and 3-4 hours to build including welding. It was the best solution to the muffler problem because of our placement and space constriants.

I haven't done any testing on the back pressure or the like, but we wrote our maps with the stock pipe. The car runs extremely well with the pipe. Every now and again we throw the loud "Bang-Bang" pipe on there to let her breath at higher RPM....but it doesnt perform as well at the lower RPM.

[Chris Boyden]

We haven't cut open the stock F4i pipe to see what the baffles look like. We'll have to rip that thing open and take a look.

What size tubing did you use for the outlet pipe on the ones that didn't work? How about the one that did?

Thanks BigT

[Charlie]

Insert Yoshimura Zyclone, make sure its freshly packed, be done. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Sam Zimmerman]

I have thought of this for a while now too. It would be pretty easy (using the impedance transfer formula or two-port networks) to find the change in sound pressure level between the exhaust ports and the tail-pipe. (Acoustically modeling the muffler might be a little tricky.) The next step would be finding the sound pressure level at the head, which I have not figured out a good way to do without destroying a microphone and/or valves. I am sure there is a simple solution that I have yet to find.

[Chris Boyden]

I would be nice to try the Yosh, but the money it takes to experiment with aftermarket mufflers is too much. Our headers are so short on the '04 car, that I think we need more muffler than most. But, that's just a gut feeling. But noise on '04 isn't a problem any more http://fsae.com/groupee_common/emoticons/icon_mad.gif
WAVE has a noise analysis feature, I don't know how to use it though or how accurately one could model the whole exhaust.

I like the idea of making several and testing.
Anybody know of a good dB meter? The old radioshack model just doesn't cut it. It read about 120 dB when the sound man said 113dB.

-Chris

[BeaverGuy]

Just because the sound guy measured 113 and you measured 120 doesn't mean that your meter was wrong. Unless you are sure you were using the same filter and tested at the same time it is entirely possible that both measurements were correct.

We tested 112 at competition when before hand we tested at 120, 100, and 140 depending on which filter was used.

[Chris Boyden]

We used the averaging filter on the radioshack meter for whatever that's worth.

[jack]

i noticed that wollongong's muffler had a very long pipe after it (like 3 or 4 feet), i dont know the first thing about acoustics, could this help noise at all?

[Eddie Martin]

We have built our own mufflers for quite a while and they are very easy to do. We buy some perforated steel sheet and fabricate some simple end caps. We make a carbon outer by buying some plumbers pipe and just laying up carbon around it with some high temperature epoxy resin. Then we get some fibre glass muffler packing and assemble. It's a lot lighter than a purchased muffler and can be built to what ever sizes you want.

The muffler is only one part of the noise equation. The frame, engine, intake and headers all make a huge difference to the noise the car makes. We have found that all these things can really add to the noise and even though the muffler was quiet the rest of the car was making a lot of noise.

The extension we have on the end of the muffler is to get the sound meter away from all the noisy things on the car.

Eddie

Don't let university get in the way of your education.

[Sam Zimmerman]

Eddie,

When making your own mufflers, do you do any acoustic modeling first or do you just "wing it"? If you model the muffler first, how accurate is your model?

[Eddie Martin]

Sam,

From memory the first muffler we made had quite a lot of research done on it and the hand calculations turned out pretty close to what it ended up. A second one was made and just done by eye, it wasn't as quiet.

[alfordda]

Our acoustic/muffler guy tells me that the long pipe after the muffler can make a difference. I think he said something like 2-3 dB's, but don't quote me on that.

[Beast]

FL Tech built our own muffler and then extended it 5" trying to get the radioshack dB meter lower than 111-112 dB. The muffler weighed in at 3.3 lbs at one point, probably ~4 lbs at competition.

Adding 5" to the muffler dropped ~1-3 dB, but sounded much quieter driving.

Adding a 2" pipe extension (like 4' long) dropped ~1-2 dB.

Restricting outlet from 2" to 1" diameter dropped 2-4 dB.

Wrapping the headers made a dramatic difference (untested), but we were measured at 101 dB at competition.

A lot of noise seems to come from the engine itself or header/exhaust port area.

Muffler was all aluminum, I think 5" dia. and ~22" long with a outlet restriction to 1" at competition.

[Greg H]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Eddie Martin:
From memory the first muffler we made had quite a lot of research done on it and the hand calculations turned out pretty close to what it ended up. A second one was made and just done by eye, it wasn't as quiet. <HR></BLOCKQUOTE>

Just wondering if you had some reference material relevant to the muffler design. I can't seem to find anything useful that really applies to our purposes and we found that doing it by eye just doesn't cut it. Anything would be helpful, thanks.

[Sam Zimmerman]

Greg

You may want to try searching the Journal of the Acoustical Society of America and the Journal of Sound and Vibration. Both of these journals have many articles on intake and exhaust modeling so I would imagine they will have some on mufflers or muffling techniques, although I have never searched for that specific topic.

Also, the ASME proceedings have some intake and exhaust papers which are much better than the SAE papers offered, check there.

Once our intake and headers are done, I am toying with the idea of designing a muffler this year. I don't see many benefits of it in terms of performance but I am twisted enough to consider it fun. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Good luck, sorry I couldn't offer more specific help. If you do start researching and have any problems let me know and I can try to lend a hand.

[Greg H]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Sam Zimmerman:
I don't see many benefits of it in terms of performance... <HR></BLOCKQUOTE>

I was mostly interested in sizing issues, weight reduction, and cost. Thanks for the info, I'll check it out.

[andrewd]

EDDIE: tisk tisk tisk http://fsae.com/groupee_common/emoticons/icon_wink.gif

GREG H:

dude if you look in any 'good' engine textbook they will most likely cover such things as engine 'silencing'

such a 'gewd' textbook is this:

Desgin and Simulation of Four-stroke engines
by Blair

[johnnySV]

bigtoyota - your muffler parameters seem quite simple (all aluminum, $35, 3-4hrs of work); i am interested to know what the design entailed ??

sheet metal rollup ?? how did you form the shape ? what was used for endcaps, etc.

[johnnySV]

is it in fact an effective means of silencing (in the muffler) to use the straight-through design w/ packing that wraps the radius of the flow path ?? (like a conventional race canister).

can packing materials and amount of packing (if you had a large diameter muffler canister) realistically drive results to quiet the system?

remeber - loud pipes save lives

..and... UNH had the best muffler last year (kidding - did anybody see that ??)

thanks,
peace.

[All Wheeler]

Newcastle had alot of success last year making a pod silencer that displayed negligible increase in back pressure over a straight-through system, with quite impressive sound reduction. It was a little complicated to make, but worth a look.

[Dr Claw]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>..and... UNH had the best muffler last year <HR></BLOCKQUOTE>

I'd have to disagree...Lawrence Tech had the best muffler last year; it was a diesel style exhaust pipe complimented with a flapper.

it was wicked cool http://fsae.com/groupee_common/emoticons/icon_smile.gif. anyone see us in our tractor trailer getup?

[BrianD]

..complete with working smoke..