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Topic: Loud exhaust

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Re: Loud exhaust (4/14)
 4/28/14 9:46am
ND4g
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The Villages, FL - USA

Vette(s):
1985 Black Corvette L98 Coupe


Joined: 3/25/2009
Posts: 14

I was most successful in removing the drone sound, when I removed the single catalytic converter, and the front and rear Y-Pipes.
I installed two "Hi-Flo Cats" and an X-Pipe. The car sounds much much better now, and without the drone. Oh, and BTW, this gave me a tremendous increase in horsepower, because the new exhaust is less restrictive than the factory configuration. No inspections here in Florida, but the muffler shop did say the replacement cats would pass the state inspection Florida had years ago.



Good luck,
Rich


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Re: Loud exhaust (5/14)
 4/28/14 7:35pm
Big Mike 49
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San Jose, CA - USA

Vette(s):
1988 Corvette / Blue Pearl


Joined: 5/10/2012
Posts: 81


Nice  Work Beer



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Re: Loud exhaust (6/14)
 4/28/14 9:30pm
Bybassett
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Muncy, PA - USA

Vette(s):
1995 torch red conv, LT1,56k,auto,loaded with options


Joined: 3/30/2014
Posts: 32

well, i had the exhaust system leaks fixed with new pipe and welding of same. put extension tips on, but it did not help at all. the roar inside the car is terrible at 1200 to 1400 rpm when i take off easy the transmission shifts into third gear at 21 mph and 4th gear at 41mph which drops the rpm right into that terrible roaring rpm zone and really annoying. is there a way programming the shift points? if i take off faster, no problem, but not a good thing to do all the time. i would like to go for a nice ride at some point without putting ear plugs in. i am considering the slim line glass pack mufflers.
Re: Loud exhaust (7/14)
 4/29/14 2:01am
davep85c4
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Posts: 254

I have owned an 85 with bone-stock exhaust since June of 1985. I've never considered it loud , objectionable, or "droney". If the Cat has been removed, and a true dual exhaust installed, this may explain the objectionably harsh sound at low RPM.

I study pipe organs. I think I understand what you're 'hearing' at the 1200-ish RPM range. On a pipe organ, it's called a "resultant".

At 1,200 RPM each bank 'speaks' at only 5 pulses per second. This is inaudible Very Low Frequency in itself, but various simultaneous frequencies create harmonics that can be heard in the audible range.  VLF is very powerful, and greatly influences sound in higher frequencies. 2 different pitches will couple to each other and produce a different frequency called a "resultant". Two specific pitches 'couple' and 'result' in producing a different pitch or harmonic.

Also, because of the firing order of the engine, there are two consecutive-firing cyls (45º crank apart) then the next pulse is 90º crank, then 90 again for each bank.. So each bank is un-even as well. Another variable to the harmonics.

The original cat converter, and the "H-Pipe" in the photos of the installation above join the two banks together. Now each pipe and muffler 'speaks' at 10 pulses per second at 1200 RPM. A much smoother, pulsing that generates fewer harmonics in the VLF range, and at least doubles the frequency of any resultants into less powerful higher frequency.

This is the primary benefit to the H-pipe: It makes the system 'speak' at a smoother, higher frequency, rate.

I hope this helps you understand the 'science' behind what your experiencing. To me, sound is fascinating because it's mathematical. All kinds of different sounds are produced as they mix together and hit the human ear. some are pleasing, and some are harsh. Think of a symphony orchestra. Or a pipe organ.



 
Re: Loud exhaust (8/14)
 4/29/14 9:49am
hcbph
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Minneapolis, MN - USA

Vette(s):
Purchased a 1986 Convert August 2013, Bright Red color with a black top, it'd already received a Tremec 5 speed upgrade along with a disc upgrade prior to purchase.


Joined: 8/16/2013
Posts: 53

ND4g
 
Good looking but one comment here.  I got the Gadgetman jack adapter so I can lift the rear using the batwing, so it slides between the pipes.  If you weld that brace between the pipes as shown, you can't use that adapter because it can't get between the pipes (from what I can tell).
For those that may not know about that adapter or seen one, it's basically a piece of IBeam shaped material that fits on a floorjack, slip it between the pipes so it's under the batwing and works well in lifting the rearend at one point.
 
Just a comment.


|UPDATED|4/29/2014 6:49:30 AM (AZT)|/UPDATED|
Re: Loud exhaust (9/14)
 4/30/14 9:14pm
Bybassett
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Muncy, PA - USA

Vette(s):
1995 torch red conv, LT1,56k,auto,loaded with options


Joined: 3/30/2014
Posts: 32

I will try for sure thanks
Re: Loud exhaust (10/14)
 5/4/14 10:14am
REDVETTE85
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NORTON, OH - USA

Vette(s):
1985 C4 red, 1985 C4 Black and dark gray


Joined: 7/9/2012
Posts: 111

 What I did was replace the cat. with a series 50 flow master 3 inch in & 2- 2 1/2 out lets used a set of muff eliminator pipes and no more drone mine was so bad I thought the back glass was gonna shatter
Re: Loud exhaust (11/14)
 5/4/14 6:14pm
davep85c4
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Posts: 254

REDVETTE85 said:  What I did was replace the cat. with a series 50 flow master 3 inch in & 2- 2 1/2 out lets used a set of muff eliminator pipes and no more drone mine was so bad I thought the back glass was gonna shatter

What was the configuration before the new cat was installed? Stock cat? Gutted stock cat? No cat, but individual pipes? And you also changed the mufflers to "no mufflers"? What type of muffler was removed?

I'm curious as to what is influencing the acoustics to produce the "drone." I've never heard it on my cars, but ocassionally I hear it on other cars near me on the freeway. I live in California, so pretty much everything has a Cat, and therefor a coupled-bank exhaust.

I think it's the choice of muffler, that produces a certain pitch with internal tuning, that then produces resultants between the two mufflers once the sound is behind the car. An H-pipe or Cat will change the resultant frequency, but not the pitch of the sound emitted form the muffler itself.

Re: Loud exhaust (12/14)
 5/9/14 7:50pm
Bybassett
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Muncy, PA - USA

Vette(s):
1995 torch red conv, LT1,56k,auto,loaded with options


Joined: 3/30/2014
Posts: 32

You did good. I had the glasspacks mufflers you suggested and drone is gone and sound is great. Thanks again. Byron
Re: Loud exhaust (13/14)
 5/16/14 5:18pm
wingnut
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Naples, FL - USA

Vette(s):
1984 C4 Mild mods.85 fuelpump,Accel ignition, TCI, shiftkit, ramAir, Boshplat plugs, duels straight, VP 106 fuel mix, 1990 wheels,, Silver/Gray 1996 LT 4 Stock muffler eliminators Torch Red ZR1 Wheels


Joined: 6/19/2011
Posts: 46

Like to  see a pic of that Batwing adp. for a floorjackQuestion

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Re: Loud exhaust (14/14)
 5/17/14 2:13pm
hcbph
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Minneapolis, MN - USA

Vette(s):
Purchased a 1986 Convert August 2013, Bright Red color with a black top, it'd already received a Tremec 5 speed upgrade along with a disc upgrade prior to purchase.


Joined: 8/16/2013
Posts: 53

wingnut said: Like to  see a pic of that Batwing adp. for a floorjackQuestion


Here's the website where it's available: http://www.corvettegadgetman.com/products3.html

It's designed to either sit on the lift cup of the jack, or remove that and bolt it onto the floorjack frame using an adapter.  The adapter didn't fit on my jack, so I took a round piece of steel that fits inside the cup and keeps it steady:

 http://i162.photobucket.com/albums/t248/hcbph/Corvette/Shop%20Tools/IM001954_zpse192ca67.jpg

http://i162.photobucket.com/albums/t248/hcbph/Corvette/Shop%20Tools/IM001953_zpse192ca67.jpg

The other thing in my pictures is a tool I designed to assist in taking out old u-joints without risking bending the yoke if it's corroded or there's a burr present.






|UPDATED|5/17/2014 11:13:50 AM (AZT)|/UPDATED|
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