Branch resonators - ways of reducing exhaust drone

gofastgeorge

gofastgeorge

Banned
Jan 24, 2008
944
0
0
Texas
Yup.

What are you using for the frequency ?
RPM where drone is the worst, multiplied by 3?
Example: 4000 rpm x # of cylinders firing per revolution = 12,000hz.
 
K

Kristian_Wraae

Member
May 18, 2007
704
0
16
53
Aarhus
Exactly. Also the calculations will change with temperature. I don't know to which extent this has been taken into account in the online calculator.
 
K

Kristian_Wraae

Member
May 18, 2007
704
0
16
53
Aarhus
It just needs to be a piece of tube in the same diameter as the rest of the exhaust. It needs to be capped in the end and it should not be an absorptive resonator since you would want as much echo transmitted back to the exhaust as possible. It doesn't have to be straight so any curved shape will do fine too.

I'm going to make it so I can vary the length from 30 to 50 cm. That should be enough to fine tune the frequency.
 
Last edited:
3p141592654

3p141592654

90T
Oct 11, 2005
3,816
16
38
Thousand Oaks, CA
The entire branch should be 4inch, but if space is an issue, smaller diameter will still work. I would think a T-junction would be best, to keep the main pipe air flow more uniform. A y-branch works too if you need it for fitment reasons. Ideally you want it in the middle of the resonant section, as that will push up the resonance by 2x. Since the supra muffler is right at the exit, the resonant section includes the muffler and the middle is hard to define without some computer simulation effort.
 
tekdeus

tekdeus

Pronounced Tek-DAY-us
Jan 23, 2006
2,115
0
0
Vancouver Canada
www.bitrontech.com
Just for your interest, I recently swapped in a divided turbo, and an SP quick spool valve with 3.5" downpipe, and my car went from somewhat loud to extremely quiet! No drone whatsoever. I was quite surprised.
 
K

Kristian_Wraae

Member
May 18, 2007
704
0
16
53
Aarhus
Yes is is astonishingly quiet in the video, but I have noticed that people in the street are now turning their heads to see what is comming...

It is around 2000 rpm (starts around 1700 and ends around 2300 rpm).

And yes the drone isn't at all apparant in the video, but it is very clear when you sit in the car.

But I have faith in the branch resonator that I'll add next week. If it works the exhaust will be perfect. Silent and will flow 800 hp....
 
Poodles

Poodles

I play with fire
Jul 22, 2006
16,757
0
0
43
Fort Worth, TX
Typical RPM for the drone, usually 5th gear at highway speeds was bad with my old exhaust (gave me a headache that left me feeling like a zombie after a roadtrip)
 
K

Kristian_Wraae

Member
May 18, 2007
704
0
16
53
Aarhus
Going to do the branch resonator next week.

The nature of the branch resonator means that it'll only work in a rather narrow frequency band but I was wondering if using a curved pipe would widen the frequency band where the branch resonator works?

The rational being that using a curved pipe would create a spectrum of lengths with the shortest path along the inner curve and the longest path along the other curve.
 
K

Kristian_Wraae

Member
May 18, 2007
704
0
16
53
Aarhus
I have been searching for some 4 inch piping for the resonator.

I'd like to make it so it'll telescope so I can adjust the length, but to do that I need some piping that is slightly larger than 4 inch.

Does anyone know if and where I can get 4+ inch piping that will slide over the 4 inch piping?
 
You must log in or register to reply here.
Top Bottom