kevinktai

Hi guys

I recently installed MagnaFlow exhaust 5 days ago.

It sounds nice, but there is a bit of drone around between 1600rpm ~ 2400rpm

Although it is not much, but it is still enough to annoy me

I have been looking online for drone solution, and I found Helmholtz resonator fix.

I found a formula on internet as below:

Let’s say the drone is worst at 2100rpms, the V6 fires 3 times per revolution. RPM is in minutes, so divide by 60 to reduce to seconds. Now you need to find the length of the wave at the frequency you just calculated. Wavelength is denoted by lambda (λ), units are meters.

f = RPM * pulses/rev * (1/60)

f = 2100 rev/min * 3 pulses/rev * (1/60)

f = 105 pulses/second = 105Hz

The formula to calculate the speed of sound vs temperature is:

I use 10C in my case.

v = 331m/s + 0.6m/s/C * T (331m.s is the speed of sound at 0C at sea level)

v = 331m/s + 0.6m/s/C * 10 = 337m/s


λ = v/f = speed of sound / frequency

λ = (337m/s)/(105Hz)

λ = 3.210 meters

This gives me the full length of full sound wave.

I can build the resonator tube by 1/4 the length of the resonant wave.

I got 3.210m / 4 = 0.8025m

So I need a 80.25cm Helmholtz tube to make my drone go away.

Here are my questions.

1.
Someone who works at the muffler shop told me to wait another 2 to 3 weeks.
The carbon buildup inside may help the drone.
Is this true?

2.
Lexus IS350 has dual pipe exhaust.
Do I need to install 80cm tube on both of the exhaust pipe?
If I need it on both of the exhaust, do I still use 80cm tube?

3.
Is there any problem with my calculation?

Much appreciated if someone can share their experience.

litesoarer

What you need is something like this.

kevinktai

[QUOTE=litesoarer;9499101]What you need is something like this.

Yes! Can you share a bit more info? Thanks a lot.

ARM350F

If you got magnaflow straight through mufflers, if you have a custom exhaust it does settle down a bit. Other wise the drone is still there. From what I have seen I believe you would need two. Ark does this for there system. If you figure this out I will definitely be using your calculations to put some on mine.

manchild

I did exactly this same thing with a drone on my Magna flow exhaust on my WRX. It works 100% and the exhaust sounded so good that people copied it.

Sphinx007

drone tubes help reduce drone but they also change the exhaust tone too.....I have recently put drone tubes on my and I noticed that I've lost some of the "bass" in the exhaust tone, it doesn't sound as deep/beefy anymore.... there is definitely a trade off

ARM350F

If I may ask where did you install the resonator?