Hey guys,

My first time posting here. I have been researching a lot for branch resonators (read a bunch of forms) to cut out the low frequency drone that is at 2000 RPM. I have stock cats with coupe mid pipe with custom installed q50 sport muffler kit. Sounds really clean but at 2000 rpm it will drone like crazy. (Even while picking up) At 3000rpm it’s clean again. I had custom installed a side branch resonator that is 16 (1/4 wave) inch installed just before the resonator pipe. (Had the shop do all the math as they told me just to let them know the rpm it’s droning at.) but it did not fix the drone. I see a lot of people had installed a 26-27-28 inch branch resonator to fix the drone in that rpm range. Would anyone be able to help me here? I spent a lot of money and don’t want to keep trying different pipe sizes till I get the drone out. I was also looking in to getting a magnaflow resonated x pipe 11358 to add to my setup but am worried that it will kill the high pitch tone and might not remove the drone. If anyone can chime in with experience with branch resonators or helmholtz resonators.

Thank you

 

Are you certain that they did the math right? Can you ask them the formula they used? Cuz it's a very exact process and it's gotta be placed exactly in the right spot with the exact length of pipe, but the math should work that out; it's a fairly accurate formula. If they did the math correctly you could need two of them (in the same place, on opposite sides of the pipe).

 

ScraggleRock, Thank you for responding,


This is the formula they used to get the tube length:


((343)/(2000 * 6 * (1/60))) / 4 = 0.42875 meters which is 16.87992126 inches.


I found the original website where they took the measurements.


I am not sure if they used the following as this one will not lead to a pipe with 16 inches:


((343)/(RPM * 4 * (1/60))) / 4


https://www.reddit.com/r/FocusST/com...or_tube_aka_j/


I will try to have pictures up by tomorrow to show you where exactly it is setup at this moment.
Thank you for your help!

 

I have uploaded the pictures.

 

more here

 

Last attachment of pictuers. Please review and let me know.

 

It's hard to tell just by pictures, but every time I've seen these, I thought I remembered them being much further back. I know every car is a bit different, but it's very important that they weld it in a very exact location. I would just bring it back to them, tell them the drone is still there and ask if they could double check their figures. I mean either way their work is gonna have to be looked over, cuz the drone is still there. Might as well just bring it up to them and see what they say.

 

Would you know of anyone else who might have done this setup before? may be you can refer them to this form.

Thank you

 

Tony @ motordyne engineering.

 

I have added sound waves

 

I have attached all the sound waves and HZ at drone level. Did message Tony, waiting on his response.

 

Took some pictures under the car at the shop today. Anyone still has info about this? Did not hear from anyone yet on the thread.

 

formula for v6 should be ((343)/(2000 * 3 * (1/60))) / 4 .... 33.75 inch long j pipe needed for the 100hz drone