New domain: www.Speed-Talk.com

The forum is currently running on the new domain and server. The old domain will remain active for a while to forward any (less frequent) visitors.
Update your bookmarks to https://www.speed-talk.com or
https://www.speed-talk.com/forum/

Exhaust hangers and interior noise levels

General engine tech -- Drag Racing to Circle Track

Moderator: Team

User avatar
BigBlockMopar
Momentary Specialist
Momentary Specialist
Posts: 207
Joined: Fri Mar 25, 2016 8:53 pm
Location: Netherlands
Contact:

Exhaust hangers and interior noise levels

Post by BigBlockMopar » Tue Mar 26, 2019 4:42 pm

Not quite Engine Tech, did anyone ever found good results with a change in interior noise-levels by changing exhaust hangers to a softer material or different/modern design?

I'm running a full 2.5" dual system in a '73 Dart with an X-pipe, Borla ProST (street) mufflers and tailpipes.
360ci engine w/11.3:1 cr, very mild street cam.

I'm OK with the sound of the exhaust on the outside but the interior noise level at around 2k rpm when accelerating is just too much, so I like to dampen the noise coming into the cabin.
Already installed self-adhesive heavy rubber antidrone sheets under the rear seat and floorboards, fabbed a stock-style cardboard w/soft dense foambarrier to block trunk-noise but this didn't appear to help much, if any.
I'm thinking the current exhaust hangers just transmit too much exhaust noise and vibration into the cabin, also because they are mounted to the floorboards (at the rear seatbelt mounts);

Currently using these just right after the mufflers and are connected to the reinforced area where the seatbelt-bolts normally would reside.
Image


Thinking of using a different type of hanger with a softer/larger rubber in between, and also mount it on the frame rails instead of floorboard, which I think would be the culprit.

JCR
Pro
Pro
Posts: 253
Joined: Sat Mar 04, 2006 12:13 pm
Location: H-Town, Tejas

Re: Exhaust hangers and interior noise levels

Post by JCR » Tue Mar 26, 2019 5:12 pm

You may want to look at what modern luxury cars use. The OEMs spend a lot of time on NVH issues. Maybe Calvin aka "exhausted" has a suggestion?

engineguyBill
HotPass
HotPass
Posts: 1076
Joined: Fri Feb 26, 2010 11:15 am
Location: Gold Canyon, AZ

Re: Exhaust hangers and interior noise levels

Post by engineguyBill » Tue Mar 26, 2019 11:09 pm

A flexible type exhaust hanger should be used in all automotive applications, mainly to isolate exhaust system vibrations. I don't think that exhaust hangers have much affect on interior noise levels though.
Bill

SAE Member (28+ years)
ASE Master Certified Engine Machinist (+ two otherASE Master Certifications)
AERA Certified Professional Engine Machinist

"Do what you can, with what you have, where you are."
- Theodore Roosevelt

User avatar
MadBill
HotPass
HotPass
Posts: 14217
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: Exhaust hangers and interior noise levels

Post by MadBill » Tue Mar 26, 2019 11:37 pm

You're right, soft hangers can help, and bolting to the floorboards out in the middle can turn them into kettledrums so identify or fab solid well-braced anchor points. Hopefully the pipes exit outside the body perimeter? (i.e., no turn-downs ahead of the axle)
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

aquartlow
New Member
New Member
Posts: 19
Joined: Sun Nov 30, 2014 9:08 pm

Re: Exhaust hangers and interior noise levels

Post by aquartlow » Tue Mar 26, 2019 11:49 pm

Covering the interior floorboards with at least a quality 80mil thickness sound deadener may be your best option to quell the interior resonances, many choices/options available.

pcnsd
Pro
Pro
Posts: 498
Joined: Thu Dec 13, 2012 12:04 am
Location: North County San Diego CA

Re: Exhaust hangers and interior noise levels

Post by pcnsd » Wed Mar 27, 2019 12:38 am

2000 rpm is in the drone rpm range for V8s assuming your system has a crossover. (100-150 hz) Build and attach one or more suppression resonators.
Drone2000rpm.png
You do not have the required permissions to view the files attached to this post.
- Paul

cjperformance
HotPass
HotPass
Posts: 3473
Joined: Tue Aug 19, 2008 7:20 am
Location: South Australia

Re: Exhaust hangers and interior noise levels

Post by cjperformance » Wed Mar 27, 2019 12:59 am

As said earlier the flexi sections make a huge difference.
Also another trick is if possible in your space is move one or bothe mufflers , one a little forward and one a little back, this alters the resonant length from each collector to dampening area in the muffler, it does not change the note out the back much but can make quite a difference to cabin noise.
Craig.

Geoff2
Guru
Guru
Posts: 1100
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: Exhaust hangers and interior noise levels

Post by Geoff2 » Wed Mar 27, 2019 2:40 am

[1] A friend removed headers from his car & fitted factory exh manifolds. Rest of the system was unchanged.... Droned with manifolds, didn't with headers.

[2] On one of my cars, I had the pipes [ 2" ] exiting ] through the rear bumper. Pipe was surrounded with silicon so there was no metal to metal contact between pipes & bumper. Removed the pipes going through the bumper & put turn downs on, so only last 12-14" of exh pipes was changed. Hangars used to support the turn downs. Through the bumper: no drone. With turn downs: drone.

I have owned enough cars & worked on enough exh systems to say as far as noise/drone: it all depends.....

You can have seemingly identical bodies, engine parts & exh systems & some will drone, some will not. Even axle ratio [ load ] make a difference.
You will have to experiment.

chimpvalet
Member
Member
Posts: 117
Joined: Wed Jun 04, 2014 2:02 am

Re: Exhaust hangers and interior noise levels

Post by chimpvalet » Wed Mar 27, 2019 12:29 pm

My rather limited experience has demonstrated that pipe layout has great potential to introduce resonance into a car's cabin. I'd go with pcnsd's advice on correcting the resonance with piping.
Cheers

groberts101
Guru
Guru
Posts: 1983
Joined: Sat Mar 08, 2008 3:08 pm
Location: Minneapolis

Re: Exhaust hangers and interior noise levels

Post by groberts101 » Wed Mar 27, 2019 4:08 pm

JCR wrote:
Tue Mar 26, 2019 5:12 pm
You may want to look at what modern luxury cars use. The OEMs spend a lot of time on NVH issues. Maybe Calvin aka "exhausted" has a suggestion?
Right on target. Hanger compliance, location(as mentioned above) and exhaust design/routing can make a HUGE difference inside the cabin. Aside from doing my own mandrel bent designs, have been doing odds and ends exhaust jobs for years and the right OEM style hangers can completely eliminate drone on many mufflers that people have associated with causing drone. The luxury cars have some of the best designs, very bulky and heavy, but they work.

I know this to be fact having fixed the issues many times and while also received many "free mufflers" that were needlessly blamed for the drone issues. Have to also be considerate of tip length as well since reverberation tendencies tend to go up, especially in the rear under that big speaker we call a trunk, as pipes get shorter and more tucked in. Don't need to stick out like flamethrowers, even just another 1-2" makes a slight difference sometimes. If fact, you can use the next pipe size up slid over your exits to adjust tip length and hear slight differences inside rrthe cabin at idle/high idle and cruise speeds. Sit in the car with the engine rev'd to around 2,000-3,000 rpm and have someone take the extensions on and off. Many are surprised at the amount of soundwaves that get reflected back under the rear of the car or truck.

User avatar
BigBlockMopar
Momentary Specialist
Momentary Specialist
Posts: 207
Joined: Fri Mar 25, 2016 8:53 pm
Location: Netherlands
Contact:

Re: Exhaust hangers and interior noise levels

Post by BigBlockMopar » Wed Mar 27, 2019 5:14 pm

Thanks for the pointers all.
The car has a full exhaust up to the rear bumper. Except for 2 'welded' bends, all bents are mandrel bent.
In my first post I said Borla-ST, but ment to say Borla-XS earlier.

Thanks for those calculations Paul. I hope to be able to 'fix' this without having to resort to Helmholtz-resonators and add more weight in the process, but will go this route if the simpler stuff doesn't work.
Instead of the floorboards I will fab new brackets to the frame rails first and use rubber O-ring donuts instead to further seperate the exhaust from the car.

The previous exhaust on the car had 2 different muffler lengths at one point. No droning. But this was with a smaller, and low CR (8.6:1) engine in front of it.

Also think a lot of noise comes from the rear axle area and trunk. I also placed a few anti-drone plates (2.2mm/86 mil) in the trunk towards the rear axle tunnel on flat areas that sounded most noisy by just tapping on them with a finger. I also fixed a length of angled aluminium on the outside of this board to limit flexing.

Some pics of the exhaust system here as it was just installed 2 years ago:
https://www.bigblockmopar.com/wp-conten ... 99CROP.jpg
https://www.bigblockmopar.com/wp-conten ... G_4906.jpg
https://www.bigblockmopar.com/wp-conten ... G_4905.jpg

In the 2nd pic one can see the hangers mounted to the floorboards. What's not shown is the hanger rod extends 'upward' in the photo and connects a little further down the exhaust to the tube (so not at the clamp at the muffler).

I also tend to believe the droning has become more pronounced over time, as if the mufflers have changed in sound, as they were rather quiet at first when new.

dfarr67
Pro
Pro
Posts: 367
Joined: Sat Jul 27, 2013 7:14 pm

Re: Exhaust hangers and interior noise levels

Post by dfarr67 » Wed Mar 27, 2019 5:28 pm

Exhaust material too, SS can ring, I believe.

Belgian1979
Guru
Guru
Posts: 3820
Joined: Sat Mar 26, 2011 11:34 am
Location: Belgium - Koersel

Re: Exhaust hangers and interior noise levels

Post by Belgian1979 » Wed Mar 27, 2019 5:48 pm

I have all the tricks mentioned above and the car still drones especially at higher engine speeds (+3000). I have been thinking that the X which is located right under the rear axle has to do something with that + the fact it has a fiberglass body.

cjperformance
HotPass
HotPass
Posts: 3473
Joined: Tue Aug 19, 2008 7:20 am
Location: South Australia

Re: Exhaust hangers and interior noise levels

Post by cjperformance » Wed Mar 27, 2019 6:31 pm

Belgian1979 wrote:
Wed Mar 27, 2019 5:48 pm
I have all the tricks mentioned above and the car still drones especially at higher engine speeds (+3000). I have been thinking that the X which is located right under the rear axle has to do something with that + the fact it has a fiberglass body.
Do you also have staggered muffler to collector lengths?
This is straigh up one of the most successful dual exhaust anti drone tricks, i have done this to some really terrible droning systems and only staggering the mufflers has made it completely drone free.
Craig.

RevTheory
HotPass
HotPass
Posts: 5207
Joined: Thu Sep 04, 2014 6:45 am

Re: Exhaust hangers and interior noise levels

Post by RevTheory » Wed Mar 27, 2019 6:43 pm

cjperformance wrote:
Wed Mar 27, 2019 6:31 pm
Do you also have staggered muffler to collector lengths?
This is straigh up one of the most successful dual exhaust anti drone tricks, i have done this to some really terrible droning systems and only staggering the mufflers has made it completely drone free.
That's pretty interesting. What happens if you have an h-pipe at a Pipemax length recommendation? Does it take enough "anti-drone length stagger" to screw that up enough to notice?

Post Reply