R3VLimited Forums

Go Back   R3VLimited Forums > E30 Technical Forums > Engine & Drivetrain > Exhaust

Reply
 
Thread Tools
Old 11-21-2016, 05:40 PM   #1
berlow94
E30 Modder
 
berlow94's Avatar
 
Join Date: Jan 2013
Location: Hancock, VT
Posts: 971
Using a J-pipe to cancel out exhaust drone

On my IX i built an exhaust pretty much from scratch. It consists of the following:

Stock manifolds down to a Y-pipe at the exact location that the factory X-pipe was located.
A single 2.5" pipe all the way back.
A Borla XS 40348 muffler. (Single 2.5" inlet, dual 2.5" outlets)

I'm getting a pretty good exhaust drone at highway speeds/RPM's.

Has anybody built an exhaust similar to this and used a tuned J-pipe to cancel out resonant drone?
__________________
The best one-stop shopping for German car parts and lifestyle: http://www.gutenparts.com/
berlow94 is offline   Reply With Quote
Old 11-21-2016, 06:20 PM   #2
Panici
Mod Crazy
 
Panici's Avatar
 
Join Date: Dec 2009
Location: Ontario, Canada
Posts: 674
Quote:
Originally Posted by berlow94 View Post
On my IX i built an exhaust pretty much from scratch. It consists of the following:

Stock manifolds down to a Y-pipe at the exact location that the factory X-pipe was located.
A single 2.5" pipe all the way back.
A Borla XS 40348 muffler. (Single 2.5" inlet, dual 2.5" outlets)

I'm getting a pretty good exhaust drone at highway speeds/RPM's.

Has anybody built an exhaust similar to this and used a tuned J-pipe to cancel out resonant drone?
I had to do a quick google to understand what a J-pipe is / does. I had never heard of it before.
http://flg8cc.com/vb4/showthread.php...nd-application

Essentially it cancels out target sound frequencies, and you choose these frequencies based on it's length.

Looks pretty cool! I think a decent external mic, laptop, and some software to do FFT (like this http://www.techmind.org/audio/specanaly.html) would do the trick to find the frequencies.

Please report back if you decide to try it!
Panici is offline   Reply With Quote
Old 11-21-2016, 06:22 PM   #3
berlow94
E30 Modder
 
berlow94's Avatar
 
Join Date: Jan 2013
Location: Hancock, VT
Posts: 971
Quote:
Originally Posted by Panici View Post
I had to do a quick google to understand what a J-pipe is / does. I had never heard of it before.
http://flg8cc.com/vb4/showthread.php...nd-application

Essentially it cancels out target sound frequencies, and you choose these frequencies based on it's length.

Looks pretty cool! I think a decent external mic, laptop, and some software to do FFT (like this http://www.techmind.org/audio/specanaly.html) would do the trick to find the frequencies.

Please report back if you decide to try it!

Off the top of my head calculations tell me that i will need a pipe .5 meters long.
From more reading, it seems that most people just weld in a Vibrant Resonator roughly where the Cat used to be to get rid of drone.

For simplicities sake i might start with the resonator and add the J-pipe later if needed.
__________________
The best one-stop shopping for German car parts and lifestyle: http://www.gutenparts.com/
berlow94 is offline   Reply With Quote
Old 11-21-2016, 08:31 PM   #4
e30davie
Wrencher
 
Join Date: Apr 2016
Location: Australia
Posts: 234
When i got my exhaust made i "converted" it from the dual ~1.75" and got them to weld in a Y-piece and single piece from then on. I asked the guy to make it 2.5" as it seemed like about the same as ~1.75", he reckoned if i went 2.5" the drone would be quite bad, he suggested 2.25" as a maximum to avoid drone....and with 2 mufflers and 2.5" there is some drone when i put the foot down but light throttle it is almost silent.

So you only have a single pipe all the way and a single muffler at the back? I would definitely suggest either a second baffled muffler in the middle or a resonator to suit your engine. Resonators are designed for a certain number of cylinders and a certain rpm to cancel out the drone.

my old 4age had a resonator in the middle and a muffler at the back. I took out the resonator and put in a second straight through muffler in order to attempt to make it quieter. It was quieter sure, but it made the resonance far worse at cruising speeds, it was almost unbearable!
e30davie is offline   Reply With Quote
Old 11-22-2016, 12:20 AM   #5
berlow94
E30 Modder
 
berlow94's Avatar
 
Join Date: Jan 2013
Location: Hancock, VT
Posts: 971
Quote:
Originally Posted by e30davie View Post
When i got my exhaust made i "converted" it from the dual ~1.75" and got them to weld in a Y-piece and single piece from then on. I asked the guy to make it 2.5" as it seemed like about the same as ~1.75", he reckoned if i went 2.5" the drone would be quite bad, he suggested 2.25" as a maximum to avoid drone....and with 2 mufflers and 2.5" there is some drone when i put the foot down but light throttle it is almost silent.

So you only have a single pipe all the way and a single muffler at the back? I would definitely suggest either a second baffled muffler in the middle or a resonator to suit your engine. Resonators are designed for a certain number of cylinders and a certain rpm to cancel out the drone.

my old 4age had a resonator in the middle and a muffler at the back. I took out the resonator and put in a second straight through muffler in order to attempt to make it quieter. It was quieter sure, but it made the resonance far worse at cruising speeds, it was almost unbearable!


Didn't really think about the size of the pipe having any effect on drone resonant frequency.
I have a single 3" pipe all the way back on my race car and there is absolutely no drone lol. Not looking for a baffled muffler. That is only a band aid fix. A j-pipe would totally cancel out a specific frequency with no additional flow restriction.


Sent from my iPhone using Tapatalk
__________________
The best one-stop shopping for German car parts and lifestyle: http://www.gutenparts.com/
berlow94 is offline   Reply With Quote
Old 12-09-2016, 03:50 PM   #6
varg
E30 Enthusiast
 
varg's Avatar
 
Join Date: May 2014
Location: Palm Beach County, FL
Posts: 1,176
My car is quiet and highway friendly with two straight through mufflers on the 3" system (a big dynomax in the center of the car and a little dual exit straight through muffler sticking out through the rear valance. A second straight through muffler would probably get you what you want, but if you don't want the exhaust to be quieter, and just want to reduce drone, a branch or helmholtz resonator is a proven option. You do need to do what Panici said and use a recording and FFT to figure out where the peak of your drone resonance is, then size your resonator accordingly. The equations necessary to size the resonator should be pretty commonly available online, since this isn't an uncommon thing for aftermarket and even OEM exhaust (and intake) systems to use.
__________________
@turbovarg
'91 318is, M20B25, T3/T04E 50 trim (14psi), megasquirt, coilovers
[project thread]

raise the lowered
varg is offline   Reply With Quote
Old 02-10-2017, 10:43 AM   #7
Sh3rpak!ng
E30 Mastermind
 
Join Date: Jan 2014
Location: Los Angeles
Posts: 1,753
I think another approach is to use an app or something to measure audio frequency. Drive the car at the rpms/speed you get drone, check the app to see what frequency the sounds comes in at, use some calculations to determine what length resonator will cancel the drone, purchase and install said resonator.

I believe the UUC Corsa RSC36 exhaust uses similar theory to control drone and tailor the frequency/sound of the exhaust. That's why it sounds so good
__________________

'89 325i OBD2 S52 BUILD THREAD
Shadetree30

Sh3rpak!ng is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 05:00 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 2004 - 2020 R3VLimited LLC