[TXTT]

2 words branch resonator. $30 at the exhaust shop. its not pretty but it fixes it . my $250 exhaust set up sounds 85.6% better than the $2k exhaust systems ive heard. borla xr1's are golden.

[Jeff@TopGearSolutions]

I'd have to disagree I think it's only 84.3% better at best

Post a vid...

[07tundra]

+1

[TXTT]

will do . im at the airport but ill get it to yall. here is some reading material. http://mkiv.supras.org.nz/articles/exhaust_drone.htm.

[rooringhusky]

Legit idea and breakdown on the link you posted..how far down stream did you add the branch? No rush but would love to see pics of location and angle

[geterdone]

Show pics, I don't like the kits that are out and want to do my own custom setup with my choice of muffler. Trying to get an exotic sound if possible, the dynomax race mufflers are my first choice so far.

[GOTMH8N]

there's another thread on here that has been talking about this and has some nice info about the length needed to kill drone down low. I'll post a link to the thread. I'm thinking about doing this to mine w/muffler delete bc the drone is ridiculous

http://www.e90post.com/forums/showthread.php?t=838213

[ZanaX]

Ok I'm interested in hearing more about what op did too. Need more DETAILS like calculating position of branch offs and what setup you had before? Pics and vids would help too!

[CannonFodder]

Originally Posted by ZanaX

Ok I'm interested in hearing more about what op did too. Need more DETAILS like calculating position of branch offs and what setup you had before? Pics and vids would help too!

Everything can be found in the other thread, but I will post here as well. For a "branch resonator" or 1/4 length resonator. Here is the calculation:

I wrote a matlab code that works pretty well for this type of resonator.

function [L] = helmholtz_DMA (temp,rpm,cyl)
%Helmholtz resonator function
%5/9/2013
%INPUT:
%temp=degrees ferinheight
%cyl= number of cylinders%rpm= rpm in which drone occurs
%OUTPUT:
%L= length of 1/4 length resonator chamber
pulse=cyl/2;
F=rpm*pulse*(1/60);
T=(temp-32)/1.8;
V=331.3+.6*T;
L1=(V/F)/4;
L=L1*39.370;end

ans = 34.4330
Published with MATLAB® R2012b

For a Helmholtz, This get a little more complex.

The first equation is the original equation for a helmholtz.

The second equation is the equation for the volume of the canister (Vo).

The third equation is equation one solved for Vo.
So.
Solving the third equation for these variables:
v= velocity of the air = 331.3+.6*(temp of exhaust gas at given point)
A= Area of neck = pi*r^2 ; where r= stock exhaust pipe size (2.5"==.0635m/2=0.03175m(<-Radius))
L= length of neck (I decided give it an arbitrary number constant) = 6" == .1524m
F= frequency in which drone is observed = rpm"observed" * 3/60

Therefore, set the solution from above equation = the second equation:
where ,
r= the radius of the helmholtz chamber (I gave this a constant of 4"==.1016m/2=0.0508m(<-Radius))
So then you just need to solve for l, which would give you the length of your chamber for a given frequency assuming that the chamber is 4" in diameter, the diameter of the stock exhaust is 2.5" and the length of the neck will be equal to 6".

Thanks phil200tdi for pointing out my error!
That should do it.

[akotten]

Originally Posted by CannonFodder

Everything can be found in the other thread, but I will post here as well. For a "branch resonator" or 1/4 length resonator. Here is the calculation:





For a Helmholtz, This get a little more complex.

Haha nice. Yay for using Matlab. Might have to make an m-file from that and save it somewhere...or make up a MathCAD sheet that does it too. Either way....very helpful, thanks.

[phil200tdi]

The standard pipe is 2.5" diameter not radius.

[CannonFodder]

Originally Posted by akotten

Haha nice. Yay for using Matlab. Might have to make an m-file from that and save it somewhere...or make up a MathCAD sheet that does it too. Either way....very helpful, thanks.

.m File for a 1/4 length resonator.

https://docs.google.com/file/d/0B1Ac...it?usp=sharing

I'll work on making a function for the Helmholtz.

[CannonFodder]

Originally Posted by phil200tdi

The standard pipe is 2.5" diameter not radius.

Good catch. I'll fix it.

[akotten]

Originally Posted by CannonFodder

.m File for a 1/4 length resonator.

https://docs.google.com/file/d/0B1Ac...it?usp=sharing

I'll work on making a function for the Helmholtz.

great, thanks!

[Marcadelic]

every exhuast shop i've talked to says they no nothing about these designs and that I would have to buy them else were so they can weld them on -_-

[CannonFodder]

Originally Posted by Marcadelic

every exhuast shop i've talked to says they no nothing about these designs and that I would have to buy them else were so they can weld them on -_-

Most exhaust fabricators haven't studied simple harmonic motion.

[Marcadelic]

Originally Posted by CannonFodder

Most exhaust fabricators haven't studied simple harmonic motion.

I know, i've come to that conclusion as well lol

you'd think they would be eager to help you figure out what you need to make some money, but that doesn't seem to be the case

[alexx03]

i wanna try this with my exhaust....but you people are way to smart for me....

[CannonFodder]

Originally Posted by alexx03

i wanna try this with my exhaust....but you people are way to smart for me....

Who you calling "you people"

[shadow191]

This stuff is pretty common with the G/Z guys since the VQ motors tend to rasp and drone a lot. HKS has been using them on their exhausts for a while and a few other companies have too. One company even makes HFC's with branch resonators.

They help a lot with the drone, but don't muffle the exhaust too much. There's still plenty of volume.

[alexx03]

Originally Posted by CannonFodder

Who you calling "you people"

all the smarter folks lol no idea what all the gibberish means

[secretsquirrel]

Originally Posted by shadow191

They help a lot with the drone, but don't muffle the exhaust too much. There's still plenty of volume.

That's perfect. I can regulate volume by picking the right exhaust. Controlling rasp and drone while using DPs is very hard.