85 Exhaust Drone question
Thread Starter
Instructor
Joined: May 2015
Posts: 108
Likes: 6
85 Exhaust Drone question
Has anybody used the new Covette Central stock style mufflers that are suppose to eliminate the annoying low rpm drone inside the car. Do they really work. The drone is so bad up until about 1500 rpm, that dont even like driving the car anymore.
Thank for any help or suggestions!!
Thank for any help or suggestions!!
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Has anybody used the new Covette Central stock style mufflers that are suppose to eliminate the annoying low rpm drone inside the car. Do they really work. The drone is so bad up until about 1500 rpm, that dont even like driving the car anymore.
Thank for any help or suggestions!!
Thank for any help or suggestions!!
...WW
Racer
Joined: Feb 2015
Posts: 279
Likes: 9
From: ridgecrest ca
? do your exhaust tip go past the valance or do they end under the valance. also see if the mufflers have at least 10 mm of clearance from anything they could touch . sometimes you have to look close to see if they clear everything . but I am betting that the tips aren't out past the valence . on my zr1 I had this problem moved the tips past the valance a problem solved . could you give the part number for the mufflers you bought .it would help in diagnosing the problem . also did you just change the mufflers or did you change from the exhaust manifolds back ?
Racer
Joined: Feb 2015
Posts: 279
Likes: 9
From: ridgecrest ca
did you change them yourself? if it is the stock style mufflers either the tips aren't out past the valance of oy don't have all the mounting hardware in its proper place . the exhaust should hang on the spring connections under the trans and rear end if for some reason the exhaust got pushed up a little it could be vibrating against something under the car . the drone is a vibration .it is one of the 2 things that is causing your problems . but I am leaning towards the tips of the exhaust not being out past the valance . rember that the tips need to have at least 10 mm of clearance when the go under the valance . hope this helps .
Thread Starter
Instructor
Joined: May 2015
Posts: 108
Likes: 6
I dont have a model number. The mufflers are older stock replacements from Corvette central. At that time they offered mufflers with both outlets functional. I replaced from the cat back and used thier Y pipe with the crossover tube. I had a shop install them at the time. Also the tops do not extend past the bumper. I will also check into that and try extensions first. Thank you!!!
Racer
Joined: Feb 2015
Posts: 279
Likes: 9
From: ridgecrest ca
I think you mean tips instead of tops .. I would ck to see if they are hitting anywhere .go back to them and tell them the tipps of the exhaust have to extend past the valance at least 1 inch .if the cry bs. then they don't know their business . I got the info I shared from the guy who owns spin tech mufflers and also sell the dr gas xpipe . in riverside ca
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
I bought stock style replacements and the drone was unbearable. In my case all the mounts were proper and the tips extended out properly. I finally welded-up the inner pipe on each muffler (deep inside where you can't see it), problem solved.
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Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
A much discussed topic: drone.
Extended tips did nothing for my car. I believe the cause is the large cavity in front of the rear fascia and a flat muffler shape to vibrate and cause more resonance that a roundish one will.
Extended tips did nothing for my car. I believe the cause is the large cavity in front of the rear fascia and a flat muffler shape to vibrate and cause more resonance that a roundish one will.
Team Owner
Joined: Dec 2000
Posts: 21,094
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From: Phila., PA burbs
? do your exhaust tip go past the valance or do they end under the valance. also see if the mufflers have at least 10 mm of clearance from anything they could touch . sometimes you have to look close to see if they clear everything . but I am betting that the tips aren't out past the valence . on my zr1 I had this problem moved the tips past the valance a problem solved . could you give the part number for the mufflers you bought .it would help in diagnosing the problem . also did you just change the mufflers or did you change from the exhaust manifolds back ?
Once you stray from the stock system you're likely gonna deal with resonance issues in certain RPM bands, especially if your car has an auto trans. The only thing that cured it on my car was putting on Corsa mufflers. They are expensive and for that reason I put off getting them for a long time, but it was one of the best things I ever did. My car is enjoyable to drive for the first time in years.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Let's recognize that the output flow area of your four exhaust tips is larger than the flow area of your single exhaust pipe from the cat con. If you restrict the area of one of your tips, the mufflers will be more effective with their noise reduction, and the resonances will be reduced. It takes some experimenting to find the right amount of restriction without doing so much that it hurts your performance. It's your decision on how much sound reduction is acceptable. It'll never be as quiet as stock, but maybe it'll be enough for your taste.
Drill a 1/4" hole in the tube near the back of the muffler that you can reach with an end wrench inside the tip. Bolt a small right angle bracket to a round baffle, such as a 2" o.d. washer. Slide this into the exhaust tip and bolt it to the 1/4" hole in the tube. The fun part of this game is that you've got a good excuse to go for a ride!
I know this suggestion will earn me a lot of daggers. I'm only trying to present an alternative, so to those who want to throw flames, please save your breath!
Drill a 1/4" hole in the tube near the back of the muffler that you can reach with an end wrench inside the tip. Bolt a small right angle bracket to a round baffle, such as a 2" o.d. washer. Slide this into the exhaust tip and bolt it to the 1/4" hole in the tube. The fun part of this game is that you've got a good excuse to go for a ride!
I know this suggestion will earn me a lot of daggers. I'm only trying to present an alternative, so to those who want to throw flames, please save your breath!
Safety Car
Joined: Jan 2014
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From: Poughkeepsie New York
Racer
Joined: Jun 2011
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I have a 96 coupe auto. When I first started with my exhaust, I got rid of the mufflers. It sounded nice outside but the drone was really bad. A friend of mine had the same exhaust set up (everything stock but no mufflers) and he told me that he eliminated the drone by getting rid of the resonator and installing an x-pipe. Got rid of the resonator, installed the x-pipe and now it sounds even better from the outside and no drone inside. Here's how my car sounds from the outside with the x-pipe.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Several have suggested an "X" pipe. The question from the OP is about his '85. These cars have a single cat con, and a single pipe from the cat con to the rear "Y" pipe, so it's impossible to put in an "X" pipe. This info may be more confusing than helpful for the OP.
Safety Car
Joined: Mar 2005
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From: Fredonia WI
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I had the same ones on my 85. The drone at low RPM (cruise) is terrible as you mentioned.
Get different mufflers -- find some that only have one functional outlet.
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
I installed headers and a x pipe on my 85, with eliminators...it was too loud so I shoved a couple of glass packs in the 2 1/2 inch outlet of the x pipe and ran the exhaust out the back....I get a lot of compliments for the sound..except from my wife.....she needs the a/c on and windows up and radio on...a real spoil sport....
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Playsdixie, would you please explain how you installed an X pipe on your '85. Had you previously installed a true dual exhaust system? How did you do the catalytic converter(s)? Is there any chance you might have a picture of your X pipe? I'm still learning.
Last edited by Hot Rod Roy; May 9, 2015 at 09:38 PM.
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
installed hedman headers, then x pipe...that eliminates the converter...from there you have to use muffler eliminators to run the pipes all the way out. I just stuck a couple of cherry bombs in the x pipes and ran pipes the rest of the way out.....I'd wouldn't say I have any drone, but the neighbors know when i'm coming or going.....
Instructor
Joined: Jun 2013
Posts: 225
Likes: 1
From: hanceville al
I put exotic muscle long tube headers and Cat delete and had true dual exhaust run on mine. The previous owner had cheap turbo mufflers on them and the drone was so bad I couldnt heard my stereo inside the car. Bought the Corsa system and couldnt be happier.