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chamber design. I'm stuck, please help!


vega

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BRAAP (a member here many people know), and my lonesome have been working on a set of mufflers that don't sound like fecal matter. I am having a difficult time finding just the mufflers (race mufflers). I DO NOT want an entire exhaust system. I do have the capability of fabing up mufflers, I have custom made equal length headers to an x pipe thus far. I DO NOT want the mufflers to have those two little connections keeping them together. I will be making this a side exit.

 

I am looking for the highest frequency/note/tone/pitch I can get. I very much enjoy the higher, crisper, cleaner sound the european v8 makes. I hate with a passion the rumble of the harley/dumptruck American v8. I have heard flowmasters on these cars. I don't know if it was the particular flowmaster series or what. But that m3 was a dumptruck. I am trying to avoid that.

 

Lower frequency sound for comparison (I am having a hard time finding the vid with the flowmasters)

htt p://ww w .youtube.com/watch ?v=jAtPDWFM7jo&feature=plcp

 

------------------

http: // w ww.youtube.c om/watch?v=5B hxWH9Dg_M

 

amazing high frequency sound

htt p://ww w.you tube .com/watch?v= SbT0IqFIfnc

 

ht tp://www.youtub e.com/watch?v=n_n8HiJ zA6A

 

Here is a cutaway of a corsa muffler.

 

htt p: //s805.beta.pho tobucket.com/use r/Phastek/media/March%202010%20Show/Corsa1.jpg.html?filters[term]=recent&filters[primary]=images

 

I am rather sure that the chambers in the muffler can be designed as such to reflect frequencies to cancel out the unwanted frequencies. I just can't find the math anywhere to determine the dimensions of the chambers.

 

I am working with 17.9 inch long primary tubes that are 1 and 5/8 in diameter, they go into a 2.5 inch collector, that then goes into a 3 inch x pipe, that will then go directly to the side exit mufflers. I am keeping it as short as possible to help retain the sound I am after.

 

This is what I am avoiding.

htt p://w ww.yout ube.co m/watch?v=klmAQFh1l-E

 

Same motor different car different mufflers...

ht tp://w ww. yo utube.c om/watch?v=IVWZMKMmjMQ

 

So does anyone know how to design the muffler to achieve this? Or designing a resonator to do this? Or simply the chambers inside the muffler to do this?

 

I am so stuck, and so is BRAAP. We are both at a loss here.

 

For some reason the forum wouldn't let me post links? I put spaces in-between to allow them to come up.

Edited by vega
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I have, I have been there done that. Wiki bla bla bla. I am still waiting for an email with a cutaway from the Taiwan company IPE. Who know if they will send out the cutaway... Regardless I don't know how to figure out how to determine the chamber size mathematically.

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If you looked at Wikipedia, you would've seen a formula.

 

Also see: http://www.sae.edu/r...Frequencies.htm

 

I did read that the helmholtz resonator used before the muffler would not work for this. It would only be able to cancel out one particular frequencey. It does not produce a frequencey via some filter, nor can it be used for a range of frequencies. You would have to have a ton of those little bulbs on the exhaust to cancel out the range that would need to be canceled

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A LOT of the sound you are looking for comes from the dimensions of the cylinder and the port, i.e., the sourch of the airflow sets the tone of the pipe. The muffler wil resonate certain tones based on the interior dimensions, not any particular baffle design or pipe diameter.

 

For instance...a trumpet is 4.5 feet long. Unrap the tubing all the way out and it's 4.5 feet. A trombone is nine feet long. See where I'm going with this?

 

Also, get a trombone player to blow you a crass note...the horn is being overblown, such that the bell resonates and rings...making a raspy, harsh tone. The main cause is airflow speed through the oriface in the mouthpiece.

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Why not make an adjustable quarter wave resonator out of two pieces of tubing and an easy seal clamp? Then you could tune it to your liking and fabricate a more carefully packaged design to fit the car.

 

People call them branch resonators too if you want to search around. Lots of aftermarket and oem designs incorporate one, usually to control a drone.

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A LOT of the sound you are looking for comes from the dimensions of the cylinder and the port, i.e., the sourch of the airflow sets the tone of the pipe. The muffler wil resonate certain tones based on the interior dimensions, not any particular baffle design or pipe diameter.

 

For instance...a trumpet is 4.5 feet long. Unrap the tubing all the way out and it's 4.5 feet. A trombone is nine feet long. See where I'm going with this?

 

Also, get a trombone player to blow you a crass note...the horn is being overblown, such that the bell resonates and rings...making a raspy, harsh tone. The main cause is airflow speed through the oriface in the mouthpiece.

 

The video i posted of the s65 on the dyno sounds just like a sbc. I disagree with you. I don't have time now to explain I will later.

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Why not make an adjustable quarter wave resonator out of two pieces of tubing and an easy seal clamp? Then you could tune it to your liking and fabricate a more carefully packaged design to fit the car.

 

People call them branch resonators too if you want to search around. Lots of aftermarket and oem designs incorporate one, usually to control a drone.

 

That is a helmhotls res.

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Not all v8s are the same. You have cross plane cranks, and single plane cranks. There is a muttitude of cylinder head desgines, and a myriad of locations for the cam(s). Ohv, sohc, dohc, etc. Also the degree angle of the v the v8- makes a difference. These ARE both 90 degree v8s, and both do use a cross plane crankshaft. The volume of the motors are different. s65 is a 4.0 lt compared to the smallest 4.8 sbc. That will make, in reality, very little difference. Keep in mind, an engine is just an air pump. The s65 is a dohc motor, the sbc has the cam in the block. Facory sbc motors do not have itbs, the s65 is an itb motor. Both are naturally aspired.

 

Regaurdless of all this, they both produce a very smilar set of of frequencies coming out of just the headers alone in that dyno video. that means that the x pipe is next in line to listen to. Great even with both withh an x pipe. they sound almost the same. Now through on the mufflers they now sound different. So what is the difference? The muffler design.

 

I sent an email to essienmen, kreisegg, and Ipe for a cutaway. We will see if the cooperate with me at all. I highly doubt they will, so I am researching how do design this myself.

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That is a helmhotls res.

 

Right. So have you already experimented with an adjustable resonator? I would use a loudspeaker design program to record SPL graphs and overlay them after each change in resonator volume. You might find adjusting tubing to be much faster than trying to use math to get your desired frequency curve. The acoustical changes are alot easier to measure than they are to predict with math, is my point of suggesting a simple, adjustable resonator. You are after an organic result (your aural sense), so why not use that sense as a design tool. I build home audio speakers and this is the standard practice to getting the particular sound you want. Math can only get you close at best.

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How would you build an adjustable one that has the exhaust flowing by it?

 

One way would be to weld a tube at ~90 degrees to the primary exhaust that is say, 12" long and the same or smaller diameter of the exhasut. Then, cut another tube that fits pretty well either the ID or OD of the 12" tube. Cut the 2nd tube about the same length and weld a cap on it. Now you have a chamber that can go from ~12" to ~20" allowing for some overlap. In order to seal and secure it for testing you could use an easyseal type clamp. It would be very easy to quick to make adjustments I think. Could be interesting to try more than one, tuned differently, to either hit two areas or widen the affected band.

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