Resonators

[Lauren]

The mini has a 4-1 header, straight pipe to a single e muffler in the back. Its LOUD. it has an annoying rasp as well. I want to put a 12-18" resonator in the mid pipe.

 

So who is famiar with them. Is the Jones turbo tube any good?. There seems to be 2 styles and louvered resonator or a turbo tube with basically two smaller pipes inside. I need to pick one. Halp

[Tinman]

The loud volume is only the first problem you might encounter. A straight through magnaflow style muffler will help to decrease the volume and rasp but you will then find drone to be an issue. A properly tuned helmholtz resonator can do wonders in decreasing or even eliminating said drone.

[zeitgeist57]

Hey, Matt...you bring up a good point. I've got a good amount of cabin noise in my BMW from a crack in the pipe near the catalytic converter. Since it's a '95 (pre-OBDII and no downstream O2 sensor after-cat) I'm looking at cutting the cat out and replace it with straight-pipe or a resonator.

 

I've researched "j-pipes" in the past and appreciate the physics that make it work. From your experience, can you put a j-pipe anywhere in the exhaust system to make a difference? Like, does it have to be further downstream or can one be installed closer to the header?

[Alfa Turbo]

Hey, Matt...you bring up a good point. I've got a good amount of cabin noise in my BMW from a crack in the pipe near the catalytic converter. Since it's a '95 (pre-OBDII and no downstream O2 sensor after-cat) I'm looking at cutting the cat out and replace it with straight-pipe or a resonator.

 

I've researched "j-pipes" in the past and appreciate the physics that make it work. From your experience, can you put a j-pipe anywhere in the exhaust system to make a difference? Like, does it have to be further downstream or can one be installed closer to the header?

 

Anywhere. Calculate the length of the standing wave (the frequency of the drone) and attach a tube 1/4 of that length anywhere along the exhaust. It's magic.

[buelliganx1]

Anywhere. Calculate the length of the standing wave (the frequency of the drone) and attach a tube 1/4 of that length anywhere along the exhaust. It's magic.

 

Any easy way of identifying the frequency of the drone? Seems like at this point there might be an app for something like that.

[Tinman]

Hey, Matt...you bring up a good point. I've got a good amount of cabin noise in my BMW from a crack in the pipe near the catalytic converter. Since it's a '95 (pre-OBDII and no downstream O2 sensor after-cat) I'm looking at cutting the cat out and replace it with straight-pipe or a resonator.

 

I've researched "j-pipes" in the past and appreciate the physics that make it work. From your experience, can you put a j-pipe anywhere in the exhaust system to make a difference? Like, does it have to be further downstream or can one be installed closer to the header?

 

Anywhere. Calculate the length of the standing wave (the frequency of the drone) and attach a tube 1/4 of that length anywhere along the exhaust. It's magic.

 

That's about the sum of it. They are typically done towards the rear of an exhaust system as that's usually the only area with enough room. One thing that might, but probably not, be worth looking at is the exhaust temperature in different parts of the system as it will have a very minor effect on the proper length of the resonator pipe.

[Alfa Turbo]

In my experience temperature and atmospheric differences are negligible. If you do the math at ambient temperature or 250*C the affect on the length of pipe caused by the speed of sound at those two temperatures is almost nothing. Many factory "mufflers" at the rear are actually a muffler on one side and a cavity on the other with a resonance tube. 4 Cylinders will require the longest resonance tubes and 8 cylinders the shortest.