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Lowering the Sound of a Performance Exhaust System by Dennis LaGrua
Started on: 07-11-2018 04:21 PM
Replies: 16 (635 views)
Last post by: Dennis LaGrua on 08-02-2018 09:52 AM
Dennis LaGrua
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Report this Post07-11-2018 04:21 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
On my 3800SC the exhaust consists of a 3" U pipe a Spintech 13" muffler and dual 2"1/2 outlets into Heddman resonator ends. Its neat compact fits where the OEM muffler was and doesn't require trunk cutting. Around town its pretty loud but for short trips to cruise nights its tolerable. On trips that run a few hours, that setup will almost make you frigin deef!
IMO, there are a few mods that I am considering that should lower the sound in the cab and they are
1. Wrap the muffler in a high temp stove insulation blanket or part of one.
2. Change to dual 2" outlet pipes
3. Insert a 3" auger in the headpipe.
4. Install a larger muffler but can't lose the trunk.
I decided to try the auger and got one from Speedway Motors for $15 on eBay. Have not installed it yet. Goal is to make the exhaust quiet enough so that long trips are more enjoyable, that the radio can be heard and conversation can more easily take place. Anyone here try any of my intended changes? If so how did they work?

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

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Report this Post07-11-2018 06:37 PM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Dennis LaGrua:

IMO, there are a few mods that I am considering that should lower the sound in the cab and they are
1. Wrap the muffler in a high temp stove insulation blanket or part of one.


I did this on the Indy.
I wrapped the muffler with "lava" header wrap and used SS straps.
I also wrapped the pipe from the catalytic convertor to the muffler.
NO difference in my case.
(Flowtech Afterburner muffler w/ Hooker dual resonator tips).

[This message has been edited by fierosound (edited 07-11-2018).]

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Report this Post07-12-2018 11:26 AM Click Here to See the Profile for darbysanSend a Private Message to darbysanEdit/Delete MessageReply w/QuoteDirect Link to This Post
Mine was similar, but smaller pipes. I used 2.5 " donut to make the header to muffler connection, then 2.25 pipes to Headman Redhot resonators. I also had a Magnaflow Cat . Sound was good but not loud, and no drone in the cab. 5 hr trips were no problem. You could try changing the outlet pipes to smaller diamater- that may help. A cat will definitely tone it down too, but there's not a lot of room, and it's a pain....

You can easily go to a larger muffler with only a small change in the trunk. Where a normal trunk slopes at the bottom toward the front of the car, make it flat instead. You lose about 2-3" on the engine side of the trunk, but none on the taillight side ( cutout piece is wedge shaped). No welding required unless you are good at it. Cut out the trunk, fold up the edge that is left on the trunk about 1/2" all the way around ( make cuts about every 3-4" to allow this), cut a piece of sheetmetal to fit laying in from the top and resting on the folded edges, then pop rivet from the bottom, seal and insulate. Some small cuts in the carpet will allow it to re-fit the new trunk. That will give enough room to tilt a larger muffler, should you choose. I ended up using a thrush welded muffler 17638. It would have fit without cutting the trunk, but it hung down about an inch below the cradle. Cutting the trunk allowed me to tilt the muffler about 30 degrees toward the rear of the car, putting the muffler above the bottom of the cradle, but left the trunk very usable. Can't even tell it's been reduced unless you really know what to look for.

BTW, I tested mine without the hedmann Resonators, and with, using a DB meter. Found no difference in sound level. I was thinking of using the stock Fiero outlets if the resonators were too quiet.

------------------
SCREW PHOTOBUCKET. All my pictures are now available at https://www.flickr.com/photos/156871275@N07/albums
'87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)

[This message has been edited by darbysan (edited 07-12-2018).]

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RayOtton
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Report this Post07-12-2018 01:25 PM Click Here to See the Profile for RayOttonSend a Private Message to RayOttonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I did the auger baffle on my NASCAR F-150.

It has a 3 inch exhaust with a low restriction muffler. It isn't too loud but it drones at highway speeds.

The baffle worked pretty good, cut the drone by about 90% making the truck much more comfortable for long distance travel.

However, at full throttle there's a ripping sound, sorta like an exhaust leak that I don't care for.

Might go with a new muffler in the fall.

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Dennis LaGrua
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Report this Post07-12-2018 05:26 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
After reading all the great tips here, I will agree that the Heddman Hot Dual Tips resonators don't reduce the sound. I used them as they mimic the look of the OEM dual tips of the Fiero and thought that they will help sound. Wrong. My 13" Spintech muffler is 3" IN with two 2 1/2" outlets. As such it is very unrestrictive on flow and sound. IMO, if we use 2 1/2" to 2" reducers and use 2" exhaust pipes to the OEM tips, I theorize that the exhaust sound will drop. Since we will then have 3" IN and dual 2" OUTS, I do not believe that flow will be affected much but sound might drop. Decided to try that before inserting the auger. From the reports I've read the auger will work great but as the above posted said the WOT sound is swoosh raspy sound. I also don't know if the auger will have a significant negative impact on reducing horsepower.
As for modifying the trunk that is not an option. My wife likes to take 12 suitcases on even a 1 overnight trip. As it is now the trunk fits two small size wheeled carry on's. She doesn't like it but the room for two pieces of luggage plus the hanging hook behind the seats makes a difference.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 07-12-2018).]

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Report this Post07-15-2018 04:25 PM Click Here to See the Profile for RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by RayOtton:

I did the auger baffle on my NASCAR F-150.

It has a 3 inch exhaust with a low restriction muffler. It isn't too loud but it drones at highway speeds.

The baffle worked pretty good, cut the drone by about 90% making the truck much more comfortable for long distance travel.

However, at full throttle there's a ripping sound, sorta like an exhaust leak that I don't care for.

Might go with a new muffler in the fall.


My 4.9 has a 2.5" (IIRC) exhaust routed in the stock Fiero manner. It's adapted up/down to a 3" cat, and has a glasspack in the stock location. Ends in a Corvette resonated tip, on only the left side.
It's loud, but it sounds good. Like others, I find the drone at highway speeds to be excessive.
I was thinking about trying an auger, too. Or maybe just replacing the glasspack with a Magnaflow, or something else that will fit.
Was your auger ahead of, or behind, the muffler?

[This message has been edited by Raydar (edited 07-15-2018).]

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Dennis LaGrua
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Report this Post07-15-2018 06:51 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Raydar:


My 4.9 has a 2.5" (IIRC) exhaust routed in the stock Fiero manner. It's adapted up/down to a 3" cat, and has a glasspack in the stock location. Ends in a Corvette resonated tip, on only the left side.
It's loud, but it sounds good. Like others, I find the drone at highway speeds to be excessive.
I was thinking about trying an auger, too. Or maybe just replacing the glasspack with a Magnaflow, or something else that will fit.
Was your auger ahead of, or behind, the muffler?




AFAIK, the auger must be placed in the pipes before the muffler on the inlet side. I can only find augers for 3" pipes. Speedway Motors has them for about $18.00. They are 11" long but can be shortened a couple of inches.
Here is my plan:
Change the exhaust pipes from 2 1/2" to 2" and put back the Fiero trumpets for the stock look. The Heddman hot tips resonators do nothing. With 3" Inlet and two 2" outlets there should not be much of flow restriction but perhaps some sounds can be restricted.
If this doesn't provide enough sound suppression then step 2 is that the auger goes in the head pipe. Some cleaning and welding is needed before I go to work so this project probably won't start for a couple of weeks.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

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Report this Post07-16-2018 06:05 AM Click Here to See the Profile for RayOttonSend a Private Message to RayOttonEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Dennis LaGrua:

AFAIK, the auger must be placed in the pipes before the muffler on the inlet side. I can only find augers for 3" pipes. Speedway Motors has them for about $18.00. They are 11" long but can be shortened a couple of inches.



I placed the auger just behind the chrome exhaust outlet, about as far from the headpipe as you could get. :-)

It didn't come with any instructions so I just did the easiest thing. Maybe if it were ahead of the muffler the rasp would be a non-issue but if I was going to go to all that effort I'd just buy a low noise muffler and skip the auger.

Honestly, I was looking for an easy fix and for $12 it seems to do the trick. Heck, the rasp even encourages me have a light foot on the pedal so the damn thing even increased my gas mileage. :-)

BTW, it only came in a 3" diameter and though my exhaust is 3" I still had to grind off a bit of the fins to get it to fit.

[This message has been edited by RayOtton (edited 07-16-2018).]

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Report this Post07-16-2018 08:38 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
Instead of placing a restriction in a performance exhaust (kinda defeats the purpose), add a helmholtz resonator.
https://www.performancetruc...minate-drone-489463/

Lots of other how-to threads and youtube videos.
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Report this Post07-16-2018 09:16 AM Click Here to See the Profile for lou_diasSend a Private Message to lou_diasEdit/Delete MessageReply w/QuoteDirect Link to This Post
With my 2.5" exhaust, I replace the cat with a 2.5" bullet-style muffler then used a performance muffler that has a 2.5" inlet and two 2" outlets similar to the stock Fiero style.
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Dennis LaGrua
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Report this Post07-16-2018 06:01 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fieroguru:

Instead of placing a restriction in a performance exhaust (kinda defeats the purpose), add a helmholtz resonator.
https://www.performancetruc...minate-drone-489463/

Lots of other how-to threads and youtube videos.


That might work but there is no room for the extra pipes. By going with dual 2" pipes out, I very much doubt that this will prove to be a significant restriction.
Lets do the math
one 2 1/2" pipe = 4.9 sq in of area
one 3" pipe = 7.07 sq in of area
two 2" pipes= 6.28 sq in of area (3.14" s in per pipe)
So by downsizing to dual 2" exhaust pipes you do add some restriction with a 3" inlet but not with a 2 1/2" inlet.

Now consider the horsepower ratings of factory engines are taken on a engine dyno without an exhaust. Then with installation in the vehicle they add an exhaust, system that is much more restrictive than what we use. I believe that my approach will result in a quieter ride and not result in much loss of RWHP. Now if you add a CAT its a totally different story as those things place a screen in the exhaust system.
------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 07-16-2018).]

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Report this Post07-16-2018 06:16 PM Click Here to See the Profile for SteelSend a Private Message to SteelEdit/Delete MessageReply w/QuoteDirect Link to This Post
A couple J-pipes added would work, also removes the irritating drone. One of the best exhaust mods you can do.
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Report this Post07-16-2018 08:59 PM Click Here to See the Profile for RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Steel:

A couple J-pipes added would work, also removes the irritating drone. One of the best exhaust mods you can do.


I've thought of that. Don't know the formulas, however. It'd be a crapshoot.
But maybe not with some research...
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Report this Post07-16-2018 11:00 PM Click Here to See the Profile for OldGuyinaGTSend a Private Message to OldGuyinaGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the main problem is the drone inside the car, are you sure you aren't getting it through the mounting of the exhaust? It's amazing how much vibration can be transmitted through the mounting points and the frame/body of the car, and it can get loud in a hurry. If you haven't already, make sure the pipes and other exhaust components don't contact anything other than the mounts, and that the mounts themselves are isolated by rubber, springs or other vibration absorbing links. In my experience, they need to be hangers of some sort - I've tried brackets and rubber bushings, and they didn't damp the frequencies in the exhaust very well.

I once had a G-body with a TorqueTech cat-back and Dynaflows, and it droned like hell in the cabin until I did this.
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Report this Post07-18-2018 10:38 AM Click Here to See the Profile for darbysanSend a Private Message to darbysanEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Dennis LaGrua:
As for modifying the trunk that is not an option. My wife likes to take 12 suitcases on even a 1 overnight trip. As it is now the trunk fits two small size wheeled carry on's. She doesn't like it but the room for two pieces of luggage plus the hanging hook behind the seats makes a difference.


Just thought I would post a couple of pictures here that I found, fo future reference. The part of the trunk removed is minimal, It eliminated just the very bottom of the trunk, where it narrows down. This mod takes about 3" total out of the depth of the trunk, but that portion is narrowd to the point that something would have to be very flexible to conform to the trunk to be totally usuable. Hope this makes sense.



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Dennis LaGrua
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Report this Post07-27-2018 09:25 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Here is the update based upon the ideas and opinions on this thread:
3" Auger doesn't fit in the U head pipe. The pipe is too short as is the muffler fitting . Will try it on the next job.
Using a Spintech Muffler with 3" In and Dual 2 1/2" outs going to two 2 1/2" Heddman Hot Tips resonators.
Using a 2 1/2" to 2 " reducer and will fit standard Fiero dual Trumpet ends to the exhaust on both sides. Figure that the smaller pipes will emit less noise.
Also eliminated all contract between the exhaust and the cradle. The muffler was contacting it in one point so I dimpled it to get a 1/4" clearance.
Next week we will see if the sound is better. It is not a significant improvement then a sheet of Dynamat goes on the cabin side firewall.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

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Dennis LaGrua
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Report this Post08-02-2018 09:52 AM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Dennis LaGrua:

Here is the update based upon the ideas and opinions on this thread:
3" Auger doesn't fit in the U head pipe. The pipe is too short as is the muffler fitting . Will try it on the next job.
Using a Spintech Muffler with 3" In and Dual 2 1/2" outs going to two 2 1/2" Heddman Hot Tips resonators. That will go
With a 2 1/2" to 2 " reducer and will fit standard Fiero dual cone ends to the exhaust on both sides. Figure that the smaller pipes will emit less noise.
Also eliminated all contract between the exhaust and the cradle. The muffler was contacting it in one point so I dimpled it to get a 1/4" clearance.
Next week we will see if the sound is better.



8/2/18 Update. Road sound test will be tomorrow. . New exhaust pipes and ends in. It looks exactly like a stock Fiero now with the cone ends. Also insulated complete exhaust from the cradle. This afternoon we will have results in using a sound meter (app on Android phone) and my impression from inside. Standing in back at idle we are around 75db. Inside the cab will be lower. Going for a 20 mile drive tomorrow .Installed a sheet of sound insulation on the inside of the heat shield on the fire wall as a sound barrier before heading out.
8/4/18 Update: Exhaust noise is significantly lowered using the dual 2" exhaust pipes from the outlets of the cross flow and the sound barrier. Still going for a lower sound by lining the engine compartment with sound insulation.
8/6/18 Update- Went out for a 20 mile drive at highway speeds. Sound inside is improved, drone reduced, but I failed to recognize the importance of the fiberglass insulation that originally lined the engine compartment. Over time that material breaks apart and in my install much of it was removed. Now I've got to find a way to put it back which is hard when everything is installed. In summation; the installation of the Fiero cone exhaust ends helps reduce noise..
------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 08-06-2018).]

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