Has anyone running catless done a j pipe exhaust? I heard around the way that j pipes are one of the best ways to quiet an exhaust down. I guess if placed in the right location the j pipe will match pressure pulses eliminating drone. Just wanted to see if anyone's heard of this as my exhaust guy hasn't. I need to do something as my current drone is loud and trashy, phew. Just no class.

I got this from a different type vehicle forum:


Basically drone is an unwanted frequency in our exhaust note that we dont want to be there. Since we cannot remove it we have to cancel it out. The J pipe is a helmholtz resonator used to do just that.

Ok application. You can use a computer listening app (frequency analyzer) or a vibration analyzer (I used the one over at the GM shop at work) to find your drone frequency. It is usually between 1400-2000 rpm cruising in 6th gear when afm is not engaged. The hz value varies but it is usually from 90-120hz. Mine was about 110hz and could rattle change in my cupholders. ;(

Now what do you do with your frequency number? Use math!! Wanna sound super smart? We will be using the speed of sound as a factor in this equation
go brag to all your friends.

Simply put, the formula for determining the length of a Helmholtz chamber used to knock out a drone frequency is:

1100 feet/second (roughly the speed of sound) divided by the target frequency you're trying to eliminate (in cycles/second) gives a full wavelength in feet per cycle. Divide this number by 4 to get a quarter wavelength (a much more convenient length to work with). Finally, multiply this wavelength by 12 to get the chamber length in inches.

So with my 110hz value it looks like this ( 1100 / 110hz ) / 4 ) x 12 = 30 inches

So the length of the helmholtz chamber needed for killing 110hz drone is 30". Now this will kill drone in a range slightly above and below 110 which is good so you dont have to have like 5 different chambers to clean out the drone.

How does it work?? Well basically the J is capped on the end and should be installed so it is out of the flow of the exhaust stream. We only want sound going in the chamber and when I does it travels all the way to the end and bounces back. When the sound bounces off the sealed end of the chamber it comes back 180* out of phase from the original sound and calcels it out voila!! A simpler example might be hooking up two subwoofers in a car and hooking up one out of phase from the other. Theres no bass right?! Same principle.


So basically I'll need to download a sound frequency app and find out what my HZ are and use the same formula find the proper length of the j pipe. I just don't understand where the right location would be to weld it in... Any suggestions? Any advice? Any pics? I'm confused

 

No one cares about this kind of stuff eh?...


It's pretty funny how "post something positive" get pages of replies on this forum but technical informative threads like this get 0.

(Crickets...)

Alright guys, drone on!

 

Gotta Love Science

 

Do you think as long as the length of the cap on the helmholtz pipe is right I can mount it anywhere in the exhaust? Just wherever it fits? That's my biggest hold up...

 

I went the easy way out and kept the muffler...

 

Haha ok.... That does not do anything to eliminate drone or quiet things down in the rpm range when you need it.

There are many factors contributing to drone or resonance sometimes even more pronounced with mufflers. When I did catless 2.5 exhaust with the stock muffler the drone was disgusting. A helmholtz pipe is going to send sound waves back into the exhaust much in the same way noise cancelling headphones work. Refer to captain slow in this video


Drone is that point in the RPM range where the waves align increasing the noise level as well as sounding worse than Conan O'briens laugh

Does anyone have any suggestions where to mount this thing in the exhaust? Opinions on if it matters, just wherever it looks cleanest?

 

I have a Mariokart downpipe and FJCW exhaust. No drone.

 

That's great thanks for the help! My car has massive drone. I need to keep a 3" exhaust Jcw is 2.5

 

Daaang I'll bump this thread one more time to ask for help.

I was kind of surprised that my previous car community experiences have been so much more helpful than the mini community. The only response this thread has gotten is from a dude that says he has no drone . The bimmer community would have been all over this one guys lol come on...

Am I the first pioneer bushwacking uncharted territory on this one? I mean it's been done before so it's not too insane of an idea. If there's no interest I guess I'll just keep it a secret upon completion. There's no point in trying to jam a square peg in a round hole right?

I know drone is a major problem with a lot of setups on these vehicles and I hear it quite a bit, I don't understand how people live with it. Just don't care?

It seems like a ton of good contributors have been banned reading through past posts. Is this forum just overrun with vendors and non contributing greenhorns nowadays or what? I'm about to give up on this site.

If you could at least point me in the direction of a more supportive modding customization type forum that would be great... mmyeea

 

I thought about a Helmholtz pipe, but there just isn't any room to put it. So this is what I did - https://www.northamericanmotoring.co...ne-solved.html

The drone is eliminated completely, and there is little to no impact on performance.

Eric