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'76 Eldorado exhaust

Started by mrmatthew, March 10, 2021, 11:42:16 PM

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mrmatthew

March 10, 2021, 11:42:16 PM Last Edit: March 11, 2021, 11:37:32 PM by mrmatthew
I just had new exhaust system installed on my 76' Eldorado. The catalytic converter was removed & new pipes , muffler & resonator installed. It's not really loud but louder than stock & too loud for me.. The muffler installer told me after the fact that removing the catalytic converter made it louder but would give more horsepower...? If this is the trade off I'd rather have it quieter. Would installing a new CAT back in the system quiet it down to sound like stock or something else like a silencer ? 

Mike Josephic CLC #3877

#1
March 10, 2021, 11:58:42 PM
What kind of replacement system did you have installed?
If, by chance, you had a stainless steel system installed
they can be a bit harsher and louder than the original
systems.

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region

mrmatthew

#2
March 11, 2021, 12:05:42 AM
Not stainless. Everything is stock minus the catalytic converter.

walt chomosh #23510

#3
March 11, 2021, 09:08:50 AM
Matthew,
  All exhaust systems are not created equal! Tubing gauge, diameter, even bends play into the equation. Then there's the muffler which really comes into play.....and the resonator which definitely also is of concern. Doing away with any crossover tube changes sound level and then there's the cat?....good luck finding your issue and please let me know what you find.....walt...tulsa,ok

chrisntam

#4
March 11, 2021, 09:55:06 AM
Try a larger muffler.
1970 Deville Convertible 
Dallas, Texas

EAM 17806

#5
March 11, 2021, 11:02:37 AM
Quote from: mrmatthew on March 10, 2021, 11:42:16 PM
I just had new exhaust system installed on my 76' Eldorado. The catalytic converter was removed & new pipes , muffler & resonator installed. It's not really loud but louder than stock & too loud for me.. The muffler installer told me after the fact that removing the catalytic converter made it louder but would give more horsepower...? If this is the trade off I'd rather have it quieter. Would installing a new CAT back in the system quiet it down to sound like stock or something else like a silencer ?
What's with your installer's brains?  Doesn't he know yet that cars that were built with catalytic converters must continue to keep it in place by FEDERAL law.  Teach him to obey the laws once in a while anyway.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

hornetball

#6
March 11, 2021, 11:30:18 AM
Before changing anything, drive the car a few hundred miles to let the new system carbon up.  The tone changes as that happens.  You may end up liking it.

Note that the 71-74 Eldos had what you are describing from the factory.

TJ Hopland

#7
March 11, 2021, 11:45:18 AM
The cat does have a big effect on the sound and the modern cats are not going to have the same sound as the old one but should help quiet it down a bit.   Ya know that angry bees in a trash can sound you hear with the 'tuner' cars?   I big start to getting that sound is removing the cat.  A low RPM V8 isn't gonna sound like those cars but still is a good example of how the sound changes.   I have had them stole recently and didn't have the time or money to replace them and the sound is quite different. 

Does it sound reasonable at idle but then get loud and drone any time you are on the gas which is a lotof the time to move a brick this size around?    If so I bet they used a 'turbo' muffler.  That isn't helping any.   Those work great if you got a 350 with dual exhaust, only 175 cubes per side and control the sound nice unless you floor it then they hit some magic balance point and get loud.   Problem when you are pushing 500 inches through them and trying to move a car around that weighs at least as much as a truck they hit that balance point pretty much any time you are on the gas.

Muffler wise I would be looking for the physically largest thing they can fit possibly intended for a truck.  You want stuff that says its OE style,  nothing that is going to improve anything.    And for performance I think most of the gain comes from getting rid of almost 50 year old stuff that just due to age isn't performing like it used to.   In a dyno or at a track there could be actual gains if you were doing before and after runs but with this kind of car on the street are those gains really gonna make a difference?  I doubt it and as you found out any little extra smile you may get from the power is ruined by the noise so its a net loss in enjoyment. 
73 Eldo convert w/FiTech EFI, over 30 years of ownership and counting
Somewhat recently deceased daily drivers, 80 Eldo Diesel & 90 CDV
And other assorted stuff I keep buying for some reason

mrmatthew

#8
March 11, 2021, 10:43:17 PM
Quote from: hornetball on March 11, 2021, 11:30:18 AM
Before changing anything, drive the car a few hundred miles to let the new system carbon up.  The tone changes as that happens.  You may end up liking it.

Note that the 71-74 Eldos had what you are describing from the factory.

I think I'll try that...If no change I'm going to install a resonator between the muffler & manifold, where the cat used to be... A guy on U tube did it to his truck & quieted down quite a bit. Thanks for everyone's input.
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